delta/go-git.git/src/expvar, branch dev.debug github.com: golang/go expvar: reduce sync.Map overhead for (*Map).Set 2017-05-02T17:13:40+00:00 Bryan C. Mills bcmills@google.com 2017-04-30T23:23:45+00:00 e9702c0c85ea1d1f0de523594d645d255e7351b1 Use Load instead of LoadOrStore in the fast path to save 1 alloc/op for existing keys. name old time/op new time/op delta IntAdd 6.39ns ± 7% 6.97ns ±19% ~ (p=0.105 n=8+8) IntAdd-6 12.3ns ± 1% 12.2ns ± 1% ~ (p=0.396 n=7+7) IntSet 6.41ns ± 6% 6.94ns ±21% ~ (p=0.168 n=8+8) IntSet-6 12.1ns ± 3% 11.7ns ± 9% ~ (p=0.496 n=7+8) FloatAdd 14.3ns ± 9% 14.7ns ± 4% ~ (p=0.088 n=8+8) FloatAdd-6 36.5ns ± 1% 36.6ns ± 0% ~ (p=0.709 n=7+6) FloatSet 6.59ns ± 7% 6.47ns ± 7% ~ (p=0.397 n=8+7) FloatSet-6 12.2ns ± 1% 12.2ns ± 2% ~ (p=0.748 n=7+7) StringSet 67.8ns ± 6% 68.7ns ± 6% ~ (p=0.342 n=8+8) StringSet-6 41.8ns ± 5% 41.7ns ± 5% ~ (p=0.979 n=8+8) MapSet 294ns ± 6% 234ns ± 4% -20.35% (p=0.000 n=8+8) MapSet-6 95.8ns ± 2% 89.4ns ± 3% -6.73% (p=0.000 n=8+8) MapSetDifferent 1.31µs ± 5% 1.07µs ± 4% -18.21% (p=0.000 n=8+8) MapSetDifferent-6 260ns ± 8% 210ns ± 9% -19.44% (p=0.000 n=8+8) MapSetString 294ns ± 6% 236ns ± 4% -19.92% (p=0.000 n=8+8) MapSetString-6 95.6ns ± 2% 89.9ns ± 2% -5.97% (p=0.000 n=7+8) MapAddSame 1.46µs ± 3% 1.46µs ± 5% ~ (p=0.721 n=8+8) MapAddSame-6 328ns ± 6% 330ns ± 4% ~ (p=0.776 n=8+8) MapAddDifferent 4.89µs ± 7% 4.98µs ± 6% ~ (p=0.505 n=8+8) MapAddDifferent-6 1.02µs ± 3% 1.01µs ± 4% ~ (p=0.352 n=7+8) MapAddSameSteadyState 62.1ns ± 7% 60.8ns ± 4% ~ (p=0.521 n=8+8) MapAddSameSteadyState-6 38.1ns ± 3% 37.7ns ± 0% ~ (p=0.185 n=7+6) MapAddDifferentSteadyState 290ns ± 5% 293ns ± 4% ~ (p=0.515 n=8+8) MapAddDifferentSteadyState-6 63.0ns ± 7% 63.7ns ±11% ~ (p=0.482 n=7+8) RealworldExpvarUsage 7.39µs ± 5% 7.51µs ± 5% ~ (p=0.382 n=8+8) RealworldExpvarUsage-6 3.07µs ±28% 3.04µs ±43% ~ (p=0.798 n=8+8) name old alloc/op new alloc/op delta IntAdd 0.00B 0.00B ~ (all equal) IntAdd-6 0.00B 0.00B ~ (all equal) IntSet 0.00B 0.00B ~ (all equal) IntSet-6 0.00B 0.00B ~ (all equal) FloatAdd 0.00B 0.00B ~ (all equal) FloatAdd-6 0.00B 0.00B ~ (all equal) FloatSet 0.00B 0.00B ~ (all equal) FloatSet-6 0.00B 0.00B ~ (all equal) StringSet 16.0B ± 0% 16.0B ± 0% ~ (all equal) StringSet-6 16.0B ± 0% 16.0B ± 0% ~ (all equal) MapSet 48.0B ± 0% 32.0B ± 0% -33.33% (p=0.000 n=8+8) MapSet-6 48.0B ± 0% 32.0B ± 0% -33.33% (p=0.000 n=8+8) MapSetDifferent 192B ± 0% 128B ± 0% -33.33% (p=0.000 n=8+8) MapSetDifferent-6 192B ± 0% 128B ± 0% -33.33% (p=0.000 n=8+8) MapSetString 48.0B ± 0% 32.0B ± 0% -33.33% (p=0.000 n=8+8) MapSetString-6 48.0B ± 0% 32.0B ± 0% -33.33% (p=0.000 n=8+8) MapAddSame 480B ± 0% 480B ± 0% ~ (all equal) MapAddSame-6 480B ± 0% 480B ± 0% ~ (all equal) MapAddDifferent 1.09kB ± 0% 1.09kB ± 0% ~ (all equal) MapAddDifferent-6 1.09kB ± 0% 1.09kB ± 0% ~ (all equal) MapAddSameSteadyState 0.00B 0.00B ~ (all equal) MapAddSameSteadyState-6 0.00B 0.00B ~ (all equal) MapAddDifferentSteadyState 0.00B 0.00B ~ (all equal) MapAddDifferentSteadyState-6 0.00B 0.00B ~ (all equal) RealworldExpvarUsage 0.00B 0.00B ~ (all equal) RealworldExpvarUsage-6 0.00B 0.00B ~ (all equal) name old allocs/op new allocs/op delta IntAdd 0.00 0.00 ~ (all equal) IntAdd-6 0.00 0.00 ~ (all equal) IntSet 0.00 0.00 ~ (all equal) IntSet-6 0.00 0.00 ~ (all equal) FloatAdd 0.00 0.00 ~ (all equal) FloatAdd-6 0.00 0.00 ~ (all equal) FloatSet 0.00 0.00 ~ (all equal) FloatSet-6 0.00 0.00 ~ (all equal) StringSet 1.00 ± 0% 1.00 ± 0% ~ (all equal) StringSet-6 1.00 ± 0% 1.00 ± 0% ~ (all equal) MapSet 3.00 ± 0% 2.00 ± 0% -33.33% (p=0.000 n=8+8) MapSet-6 3.00 ± 0% 2.00 ± 0% -33.33% (p=0.000 n=8+8) MapSetDifferent 12.0 ± 0% 8.0 ± 0% -33.33% (p=0.000 n=8+8) MapSetDifferent-6 12.0 ± 0% 8.0 ± 0% -33.33% (p=0.000 n=8+8) MapSetString 3.00 ± 0% 2.00 ± 0% -33.33% (p=0.000 n=8+8) MapSetString-6 3.00 ± 0% 2.00 ± 0% -33.33% (p=0.000 n=8+8) MapAddSame 11.0 ± 0% 11.0 ± 0% ~ (all equal) MapAddSame-6 11.0 ± 0% 11.0 ± 0% ~ (all equal) MapAddDifferent 31.0 ± 0% 31.0 ± 0% ~ (all equal) MapAddDifferent-6 31.0 ± 0% 31.0 ± 0% ~ (all equal) MapAddSameSteadyState 0.00 0.00 ~ (all equal) MapAddSameSteadyState-6 0.00 0.00 ~ (all equal) MapAddDifferentSteadyState 0.00 0.00 ~ (all equal) MapAddDifferentSteadyState-6 0.00 0.00 ~ (all equal) RealworldExpvarUsage 0.00 0.00 ~ (all equal) RealworldExpvarUsage-6 0.00 0.00 ~ (all equal) https://perf.golang.org/search?q=upload:20170501.1 Change-Id: I28fc3906473f2b7307f6d1ae05a8d9b01ef8a6f8 Reviewed-on: https://go-review.googlesource.com/42211 Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org> 
Use Load instead of LoadOrStore in the fast path to save 1 alloc/op
for existing keys.

name                          old time/op    new time/op    delta
IntAdd                          6.39ns ± 7%    6.97ns ±19%     ~     (p=0.105 n=8+8)
IntAdd-6                        12.3ns ± 1%    12.2ns ± 1%     ~     (p=0.396 n=7+7)
IntSet                          6.41ns ± 6%    6.94ns ±21%     ~     (p=0.168 n=8+8)
IntSet-6                        12.1ns ± 3%    11.7ns ± 9%     ~     (p=0.496 n=7+8)
FloatAdd                        14.3ns ± 9%    14.7ns ± 4%     ~     (p=0.088 n=8+8)
FloatAdd-6                      36.5ns ± 1%    36.6ns ± 0%     ~     (p=0.709 n=7+6)
FloatSet                        6.59ns ± 7%    6.47ns ± 7%     ~     (p=0.397 n=8+7)
FloatSet-6                      12.2ns ± 1%    12.2ns ± 2%     ~     (p=0.748 n=7+7)
StringSet                       67.8ns ± 6%    68.7ns ± 6%     ~     (p=0.342 n=8+8)
StringSet-6                     41.8ns ± 5%    41.7ns ± 5%     ~     (p=0.979 n=8+8)
MapSet                           294ns ± 6%     234ns ± 4%  -20.35%  (p=0.000 n=8+8)
MapSet-6                        95.8ns ± 2%    89.4ns ± 3%   -6.73%  (p=0.000 n=8+8)
MapSetDifferent                 1.31µs ± 5%    1.07µs ± 4%  -18.21%  (p=0.000 n=8+8)
MapSetDifferent-6                260ns ± 8%     210ns ± 9%  -19.44%  (p=0.000 n=8+8)
MapSetString                     294ns ± 6%     236ns ± 4%  -19.92%  (p=0.000 n=8+8)
MapSetString-6                  95.6ns ± 2%    89.9ns ± 2%   -5.97%  (p=0.000 n=7+8)
MapAddSame                      1.46µs ± 3%    1.46µs ± 5%     ~     (p=0.721 n=8+8)
MapAddSame-6                     328ns ± 6%     330ns ± 4%     ~     (p=0.776 n=8+8)
MapAddDifferent                 4.89µs ± 7%    4.98µs ± 6%     ~     (p=0.505 n=8+8)
MapAddDifferent-6               1.02µs ± 3%    1.01µs ± 4%     ~     (p=0.352 n=7+8)
MapAddSameSteadyState           62.1ns ± 7%    60.8ns ± 4%     ~     (p=0.521 n=8+8)
MapAddSameSteadyState-6         38.1ns ± 3%    37.7ns ± 0%     ~     (p=0.185 n=7+6)
MapAddDifferentSteadyState       290ns ± 5%     293ns ± 4%     ~     (p=0.515 n=8+8)
MapAddDifferentSteadyState-6    63.0ns ± 7%    63.7ns ±11%     ~     (p=0.482 n=7+8)
RealworldExpvarUsage            7.39µs ± 5%    7.51µs ± 5%     ~     (p=0.382 n=8+8)
RealworldExpvarUsage-6          3.07µs ±28%    3.04µs ±43%     ~     (p=0.798 n=8+8)

name                          old alloc/op   new alloc/op   delta
IntAdd                           0.00B          0.00B          ~     (all equal)
IntAdd-6                         0.00B          0.00B          ~     (all equal)
IntSet                           0.00B          0.00B          ~     (all equal)
IntSet-6                         0.00B          0.00B          ~     (all equal)
FloatAdd                         0.00B          0.00B          ~     (all equal)
FloatAdd-6                       0.00B          0.00B          ~     (all equal)
FloatSet                         0.00B          0.00B          ~     (all equal)
FloatSet-6                       0.00B          0.00B          ~     (all equal)
StringSet                        16.0B ± 0%     16.0B ± 0%     ~     (all equal)
StringSet-6                      16.0B ± 0%     16.0B ± 0%     ~     (all equal)
MapSet                           48.0B ± 0%     32.0B ± 0%  -33.33%  (p=0.000 n=8+8)
MapSet-6                         48.0B ± 0%     32.0B ± 0%  -33.33%  (p=0.000 n=8+8)
MapSetDifferent                   192B ± 0%      128B ± 0%  -33.33%  (p=0.000 n=8+8)
MapSetDifferent-6                 192B ± 0%      128B ± 0%  -33.33%  (p=0.000 n=8+8)
MapSetString                     48.0B ± 0%     32.0B ± 0%  -33.33%  (p=0.000 n=8+8)
MapSetString-6                   48.0B ± 0%     32.0B ± 0%  -33.33%  (p=0.000 n=8+8)
MapAddSame                        480B ± 0%      480B ± 0%     ~     (all equal)
MapAddSame-6                      480B ± 0%      480B ± 0%     ~     (all equal)
MapAddDifferent                 1.09kB ± 0%    1.09kB ± 0%     ~     (all equal)
MapAddDifferent-6               1.09kB ± 0%    1.09kB ± 0%     ~     (all equal)
MapAddSameSteadyState            0.00B          0.00B          ~     (all equal)
MapAddSameSteadyState-6          0.00B          0.00B          ~     (all equal)
MapAddDifferentSteadyState       0.00B          0.00B          ~     (all equal)
MapAddDifferentSteadyState-6     0.00B          0.00B          ~     (all equal)
RealworldExpvarUsage             0.00B          0.00B          ~     (all equal)
RealworldExpvarUsage-6           0.00B          0.00B          ~     (all equal)

name                          old allocs/op  new allocs/op  delta
IntAdd                            0.00           0.00          ~     (all equal)
IntAdd-6                          0.00           0.00          ~     (all equal)
IntSet                            0.00           0.00          ~     (all equal)
IntSet-6                          0.00           0.00          ~     (all equal)
FloatAdd                          0.00           0.00          ~     (all equal)
FloatAdd-6                        0.00           0.00          ~     (all equal)
FloatSet                          0.00           0.00          ~     (all equal)
FloatSet-6                        0.00           0.00          ~     (all equal)
StringSet                         1.00 ± 0%      1.00 ± 0%     ~     (all equal)
StringSet-6                       1.00 ± 0%      1.00 ± 0%     ~     (all equal)
MapSet                            3.00 ± 0%      2.00 ± 0%  -33.33%  (p=0.000 n=8+8)
MapSet-6                          3.00 ± 0%      2.00 ± 0%  -33.33%  (p=0.000 n=8+8)
MapSetDifferent                   12.0 ± 0%       8.0 ± 0%  -33.33%  (p=0.000 n=8+8)
MapSetDifferent-6                 12.0 ± 0%       8.0 ± 0%  -33.33%  (p=0.000 n=8+8)
MapSetString                      3.00 ± 0%      2.00 ± 0%  -33.33%  (p=0.000 n=8+8)
MapSetString-6                    3.00 ± 0%      2.00 ± 0%  -33.33%  (p=0.000 n=8+8)
MapAddSame                        11.0 ± 0%      11.0 ± 0%     ~     (all equal)
MapAddSame-6                      11.0 ± 0%      11.0 ± 0%     ~     (all equal)
MapAddDifferent                   31.0 ± 0%      31.0 ± 0%     ~     (all equal)
MapAddDifferent-6                 31.0 ± 0%      31.0 ± 0%     ~     (all equal)
MapAddSameSteadyState             0.00           0.00          ~     (all equal)
MapAddSameSteadyState-6           0.00           0.00          ~     (all equal)
MapAddDifferentSteadyState        0.00           0.00          ~     (all equal)
MapAddDifferentSteadyState-6      0.00           0.00          ~     (all equal)
RealworldExpvarUsage              0.00           0.00          ~     (all equal)
RealworldExpvarUsage-6            0.00           0.00          ~     (all equal)

https://perf.golang.org/search?q=upload:20170501.1

Change-Id: I28fc3906473f2b7307f6d1ae05a8d9b01ef8a6f8
Reviewed-on: https://go-review.googlesource.com/42211
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
expvar: replace RWMutex usage with sync.Map and atomics 2017-04-28T21:59:55+00:00 Bryan C. Mills bcmills@google.com 2017-02-16T22:44:16+00:00 fb0fe4277d8393110569b66944dffb4b2c2c1687 Int and Float already used atomics. When many goroutines on many CPUs concurrently update a StringSet or a Map with different keys per goroutine, this change results in dramatic steady-state speedups. This change does add some overhead for single-CPU and ephemeral maps. I believe that is mostly due to an increase in allocations per call (to pack the map keys and values into interface{} values that may escape into the heap). With better inlining and/or escape analysis, the single-CPU penalty may decline somewhat. There are still two RWMutexes in the package: one for the keys in the global "vars" map, and one for the keys in individual Map variables. Those RWMutexes could also be eliminated, but avoiding excessive allocations when adding new keys would require care. The remaining RWMutexes are only acquired in Do functions, which I believe are not typically on the fast path. updates #17973 updates #18177 name old time/op new time/op delta StringSet 65.9ns ± 8% 55.7ns ± 1% -15.46% (p=0.000 n=8+7) StringSet-6 416ns ±22% 127ns ±19% -69.37% (p=0.000 n=8+8) StringSet-48 309ns ± 8% 94ns ± 3% -69.43% (p=0.001 n=7+7) name old alloc/op new alloc/op delta StringSet 0.00B 16.00B ± 0% +Inf% (p=0.000 n=8+8) StringSet-6 0.00B 16.00B ± 0% +Inf% (p=0.000 n=8+8) StringSet-48 0.00B 16.00B ± 0% +Inf% (p=0.000 n=8+8) name old allocs/op new allocs/op delta StringSet 0.00 1.00 ± 0% +Inf% (p=0.000 n=8+8) StringSet-6 0.00 1.00 ± 0% +Inf% (p=0.000 n=8+8) StringSet-48 0.00 1.00 ± 0% +Inf% (p=0.000 n=8+8) https://perf.golang.org/search?q=upload:20170427.3 name old time/op new time/op delta IntAdd 5.64ns ± 3% 5.58ns ± 1% ~ (p=0.185 n=8+8) IntAdd-6 18.6ns ±32% 21.4ns ±21% ~ (p=0.078 n=8+8) IntAdd-48 19.6ns ±13% 20.6ns ±19% ~ (p=0.702 n=8+8) IntSet 5.50ns ± 1% 5.48ns ± 0% ~ (p=0.222 n=7+8) IntSet-6 18.5ns ±16% 20.4ns ±30% ~ (p=0.314 n=8+8) IntSet-48 19.7ns ±12% 20.4ns ±16% ~ (p=0.522 n=8+8) FloatAdd 14.5ns ± 1% 14.6ns ± 2% ~ (p=0.237 n=7+8) FloatAdd-6 69.9ns ±13% 68.4ns ± 7% ~ (p=0.557 n=7+7) FloatAdd-48 110ns ± 9% 109ns ± 6% ~ (p=0.667 n=8+8) FloatSet 7.62ns ± 3% 7.64ns ± 5% ~ (p=0.939 n=8+8) FloatSet-6 20.7ns ±22% 21.0ns ±23% ~ (p=0.959 n=8+8) FloatSet-48 20.4ns ±24% 20.8ns ±19% ~ (p=0.899 n=8+8) MapSet 88.1ns ±15% 200.9ns ± 7% +128.11% (p=0.000 n=8+8) MapSet-6 453ns ±12% 202ns ± 8% -55.43% (p=0.000 n=8+8) MapSet-48 432ns ±12% 240ns ±15% -44.49% (p=0.000 n=8+8) MapSetDifferent 349ns ± 1% 876ns ± 2% +151.08% (p=0.001 n=6+7) MapSetDifferent-6 1.74µs ±32% 0.25µs ±17% -85.71% (p=0.000 n=8+8) MapSetDifferent-48 1.77µs ±10% 0.14µs ± 2% -91.84% (p=0.000 n=8+8) MapSetString 88.1ns ± 7% 205.3ns ± 5% +132.98% (p=0.001 n=7+7) MapSetString-6 438ns ±30% 205ns ± 9% -53.15% (p=0.000 n=8+8) MapSetString-48 419ns ±14% 241ns ±15% -42.39% (p=0.000 n=8+8) MapAddSame 686ns ± 9% 1010ns ± 5% +47.41% (p=0.000 n=8+8) MapAddSame-6 238ns ±10% 300ns ±11% +26.22% (p=0.000 n=8+8) MapAddSame-48 366ns ± 4% 483ns ± 3% +32.06% (p=0.000 n=8+8) MapAddDifferent 1.96µs ± 4% 3.24µs ± 6% +65.58% (p=0.000 n=8+8) MapAddDifferent-6 553ns ± 3% 948ns ± 8% +71.43% (p=0.000 n=7+8) MapAddDifferent-48 548ns ± 4% 1242ns ±10% +126.81% (p=0.000 n=8+8) MapAddSameSteadyState 31.5ns ± 7% 41.7ns ± 6% +32.61% (p=0.000 n=8+8) MapAddSameSteadyState-6 239ns ± 7% 101ns ±30% -57.53% (p=0.000 n=7+8) MapAddSameSteadyState-48 152ns ± 4% 85ns ±13% -43.84% (p=0.000 n=8+7) MapAddDifferentSteadyState 151ns ± 5% 177ns ± 1% +17.32% (p=0.001 n=8+6) MapAddDifferentSteadyState-6 861ns ±15% 62ns ±23% -92.85% (p=0.000 n=8+8) MapAddDifferentSteadyState-48 617ns ± 2% 20ns ±14% -96.75% (p=0.000 n=8+8) RealworldExpvarUsage 4.33µs ± 4% 4.48µs ± 6% ~ (p=0.336 n=8+7) RealworldExpvarUsage-6 2.12µs ±20% 2.28µs ±10% ~ (p=0.228 n=8+6) RealworldExpvarUsage-48 1.23µs ±19% 1.36µs ±16% ~ (p=0.152 n=7+8) name old alloc/op new alloc/op delta IntAdd 0.00B 0.00B ~ (all equal) IntAdd-6 0.00B 0.00B ~ (all equal) IntAdd-48 0.00B 0.00B ~ (all equal) IntSet 0.00B 0.00B ~ (all equal) IntSet-6 0.00B 0.00B ~ (all equal) IntSet-48 0.00B 0.00B ~ (all equal) FloatAdd 0.00B 0.00B ~ (all equal) FloatAdd-6 0.00B 0.00B ~ (all equal) FloatAdd-48 0.00B 0.00B ~ (all equal) FloatSet 0.00B 0.00B ~ (all equal) FloatSet-6 0.00B 0.00B ~ (all equal) FloatSet-48 0.00B 0.00B ~ (all equal) MapSet 0.00B 48.00B ± 0% +Inf% (p=0.000 n=8+8) MapSet-6 0.00B 48.00B ± 0% +Inf% (p=0.000 n=8+8) MapSet-48 0.00B 48.00B ± 0% +Inf% (p=0.000 n=8+8) MapSetDifferent 0.00B 192.00B ± 0% +Inf% (p=0.000 n=8+8) MapSetDifferent-6 0.00B 192.00B ± 0% +Inf% (p=0.000 n=8+8) MapSetDifferent-48 0.00B 192.00B ± 0% +Inf% (p=0.000 n=8+8) MapSetString 0.00B 48.00B ± 0% +Inf% (p=0.000 n=8+8) MapSetString-6 0.00B 48.00B ± 0% +Inf% (p=0.000 n=8+8) MapSetString-48 0.00B 48.00B ± 0% +Inf% (p=0.000 n=8+8) MapAddSame 456B ± 0% 480B ± 0% +5.26% (p=0.000 n=8+8) MapAddSame-6 456B ± 0% 480B ± 0% +5.26% (p=0.000 n=8+8) MapAddSame-48 456B ± 0% 480B ± 0% +5.26% (p=0.000 n=8+8) MapAddDifferent 672B ± 0% 1088B ± 0% +61.90% (p=0.000 n=8+8) MapAddDifferent-6 672B ± 0% 1088B ± 0% +61.90% (p=0.000 n=8+8) MapAddDifferent-48 672B ± 0% 1088B ± 0% +61.90% (p=0.000 n=8+8) MapAddSameSteadyState 0.00B 0.00B ~ (all equal) MapAddSameSteadyState-6 0.00B 0.00B ~ (all equal) MapAddSameSteadyState-48 0.00B 0.00B ~ (all equal) MapAddDifferentSteadyState 0.00B 0.00B ~ (all equal) MapAddDifferentSteadyState-6 0.00B 0.00B ~ (all equal) MapAddDifferentSteadyState-48 0.00B 0.00B ~ (all equal) RealworldExpvarUsage 0.00B 0.00B ~ (all equal) RealworldExpvarUsage-6 0.00B 0.00B ~ (all equal) RealworldExpvarUsage-48 0.00B 0.00B ~ (all equal) name old allocs/op new allocs/op delta IntAdd 0.00 0.00 ~ (all equal) IntAdd-6 0.00 0.00 ~ (all equal) IntAdd-48 0.00 0.00 ~ (all equal) IntSet 0.00 0.00 ~ (all equal) IntSet-6 0.00 0.00 ~ (all equal) IntSet-48 0.00 0.00 ~ (all equal) FloatAdd 0.00 0.00 ~ (all equal) FloatAdd-6 0.00 0.00 ~ (all equal) FloatAdd-48 0.00 0.00 ~ (all equal) FloatSet 0.00 0.00 ~ (all equal) FloatSet-6 0.00 0.00 ~ (all equal) FloatSet-48 0.00 0.00 ~ (all equal) MapSet 0.00 3.00 ± 0% +Inf% (p=0.000 n=8+8) MapSet-6 0.00 3.00 ± 0% +Inf% (p=0.000 n=8+8) MapSet-48 0.00 3.00 ± 0% +Inf% (p=0.000 n=8+8) MapSetDifferent 0.00 12.00 ± 0% +Inf% (p=0.000 n=8+8) MapSetDifferent-6 0.00 12.00 ± 0% +Inf% (p=0.000 n=8+8) MapSetDifferent-48 0.00 12.00 ± 0% +Inf% (p=0.000 n=8+8) MapSetString 0.00 3.00 ± 0% +Inf% (p=0.000 n=8+8) MapSetString-6 0.00 3.00 ± 0% +Inf% (p=0.000 n=8+8) MapSetString-48 0.00 3.00 ± 0% +Inf% (p=0.000 n=8+8) MapAddSame 6.00 ± 0% 11.00 ± 0% +83.33% (p=0.000 n=8+8) MapAddSame-6 6.00 ± 0% 11.00 ± 0% +83.33% (p=0.000 n=8+8) MapAddSame-48 6.00 ± 0% 11.00 ± 0% +83.33% (p=0.000 n=8+8) MapAddDifferent 14.0 ± 0% 31.0 ± 0% +121.43% (p=0.000 n=8+8) MapAddDifferent-6 14.0 ± 0% 31.0 ± 0% +121.43% (p=0.000 n=8+8) MapAddDifferent-48 14.0 ± 0% 31.0 ± 0% +121.43% (p=0.000 n=8+8) MapAddSameSteadyState 0.00 0.00 ~ (all equal) MapAddSameSteadyState-6 0.00 0.00 ~ (all equal) MapAddSameSteadyState-48 0.00 0.00 ~ (all equal) MapAddDifferentSteadyState 0.00 0.00 ~ (all equal) MapAddDifferentSteadyState-6 0.00 0.00 ~ (all equal) MapAddDifferentSteadyState-48 0.00 0.00 ~ (all equal) RealworldExpvarUsage 0.00 0.00 ~ (all equal) RealworldExpvarUsage-6 0.00 0.00 ~ (all equal) RealworldExpvarUsage-48 0.00 0.00 ~ (all equal) https://perf.golang.org/search?q=upload:20170427.1 Change-Id: I388b2e8a3cadb84fc1418af8acfc27338f799273 Reviewed-on: https://go-review.googlesource.com/41930 Run-TryBot: Bryan Mills <bcmills@google.com> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Ian Lance Taylor <iant@golang.org> 
Int and Float already used atomics.

When many goroutines on many CPUs concurrently update a StringSet or a
Map with different keys per goroutine, this change results in dramatic
steady-state speedups.

This change does add some overhead for single-CPU and ephemeral maps.
I believe that is mostly due to an increase in allocations per call
(to pack the map keys and values into interface{} values that may
escape into the heap). With better inlining and/or escape analysis,
the single-CPU penalty may decline somewhat.

There are still two RWMutexes in the package: one for the keys in the
global "vars" map, and one for the keys in individual Map variables.

Those RWMutexes could also be eliminated, but avoiding excessive
allocations when adding new keys would require care. The remaining
RWMutexes are only acquired in Do functions, which I believe are not
typically on the fast path.

updates #17973
updates #18177

name             old time/op    new time/op    delta
StringSet          65.9ns ± 8%    55.7ns ± 1%   -15.46%  (p=0.000 n=8+7)
StringSet-6         416ns ±22%     127ns ±19%   -69.37%  (p=0.000 n=8+8)
StringSet-48        309ns ± 8%      94ns ± 3%   -69.43%  (p=0.001 n=7+7)

name             old alloc/op   new alloc/op   delta
StringSet           0.00B         16.00B ± 0%     +Inf%  (p=0.000 n=8+8)
StringSet-6         0.00B         16.00B ± 0%     +Inf%  (p=0.000 n=8+8)
StringSet-48        0.00B         16.00B ± 0%     +Inf%  (p=0.000 n=8+8)

name             old allocs/op  new allocs/op  delta
StringSet            0.00           1.00 ± 0%     +Inf%  (p=0.000 n=8+8)
StringSet-6          0.00           1.00 ± 0%     +Inf%  (p=0.000 n=8+8)
StringSet-48         0.00           1.00 ± 0%     +Inf%  (p=0.000 n=8+8)

https://perf.golang.org/search?q=upload:20170427.3

name                           old time/op    new time/op    delta
IntAdd                           5.64ns ± 3%    5.58ns ± 1%      ~     (p=0.185 n=8+8)
IntAdd-6                         18.6ns ±32%    21.4ns ±21%      ~     (p=0.078 n=8+8)
IntAdd-48                        19.6ns ±13%    20.6ns ±19%      ~     (p=0.702 n=8+8)
IntSet                           5.50ns ± 1%    5.48ns ± 0%      ~     (p=0.222 n=7+8)
IntSet-6                         18.5ns ±16%    20.4ns ±30%      ~     (p=0.314 n=8+8)
IntSet-48                        19.7ns ±12%    20.4ns ±16%      ~     (p=0.522 n=8+8)
FloatAdd                         14.5ns ± 1%    14.6ns ± 2%      ~     (p=0.237 n=7+8)
FloatAdd-6                       69.9ns ±13%    68.4ns ± 7%      ~     (p=0.557 n=7+7)
FloatAdd-48                       110ns ± 9%     109ns ± 6%      ~     (p=0.667 n=8+8)
FloatSet                         7.62ns ± 3%    7.64ns ± 5%      ~     (p=0.939 n=8+8)
FloatSet-6                       20.7ns ±22%    21.0ns ±23%      ~     (p=0.959 n=8+8)
FloatSet-48                      20.4ns ±24%    20.8ns ±19%      ~     (p=0.899 n=8+8)
MapSet                           88.1ns ±15%   200.9ns ± 7%  +128.11%  (p=0.000 n=8+8)
MapSet-6                          453ns ±12%     202ns ± 8%   -55.43%  (p=0.000 n=8+8)
MapSet-48                         432ns ±12%     240ns ±15%   -44.49%  (p=0.000 n=8+8)
MapSetDifferent                   349ns ± 1%     876ns ± 2%  +151.08%  (p=0.001 n=6+7)
MapSetDifferent-6                1.74µs ±32%    0.25µs ±17%   -85.71%  (p=0.000 n=8+8)
MapSetDifferent-48               1.77µs ±10%    0.14µs ± 2%   -91.84%  (p=0.000 n=8+8)
MapSetString                     88.1ns ± 7%   205.3ns ± 5%  +132.98%  (p=0.001 n=7+7)
MapSetString-6                    438ns ±30%     205ns ± 9%   -53.15%  (p=0.000 n=8+8)
MapSetString-48                   419ns ±14%     241ns ±15%   -42.39%  (p=0.000 n=8+8)
MapAddSame                        686ns ± 9%    1010ns ± 5%   +47.41%  (p=0.000 n=8+8)
MapAddSame-6                      238ns ±10%     300ns ±11%   +26.22%  (p=0.000 n=8+8)
MapAddSame-48                     366ns ± 4%     483ns ± 3%   +32.06%  (p=0.000 n=8+8)
MapAddDifferent                  1.96µs ± 4%    3.24µs ± 6%   +65.58%  (p=0.000 n=8+8)
MapAddDifferent-6                 553ns ± 3%     948ns ± 8%   +71.43%  (p=0.000 n=7+8)
MapAddDifferent-48                548ns ± 4%    1242ns ±10%  +126.81%  (p=0.000 n=8+8)
MapAddSameSteadyState            31.5ns ± 7%    41.7ns ± 6%   +32.61%  (p=0.000 n=8+8)
MapAddSameSteadyState-6           239ns ± 7%     101ns ±30%   -57.53%  (p=0.000 n=7+8)
MapAddSameSteadyState-48          152ns ± 4%      85ns ±13%   -43.84%  (p=0.000 n=8+7)
MapAddDifferentSteadyState        151ns ± 5%     177ns ± 1%   +17.32%  (p=0.001 n=8+6)
MapAddDifferentSteadyState-6      861ns ±15%      62ns ±23%   -92.85%  (p=0.000 n=8+8)
MapAddDifferentSteadyState-48     617ns ± 2%      20ns ±14%   -96.75%  (p=0.000 n=8+8)
RealworldExpvarUsage             4.33µs ± 4%    4.48µs ± 6%      ~     (p=0.336 n=8+7)
RealworldExpvarUsage-6           2.12µs ±20%    2.28µs ±10%      ~     (p=0.228 n=8+6)
RealworldExpvarUsage-48          1.23µs ±19%    1.36µs ±16%      ~     (p=0.152 n=7+8)

name                           old alloc/op   new alloc/op   delta
IntAdd                            0.00B          0.00B           ~     (all equal)
IntAdd-6                          0.00B          0.00B           ~     (all equal)
IntAdd-48                         0.00B          0.00B           ~     (all equal)
IntSet                            0.00B          0.00B           ~     (all equal)
IntSet-6                          0.00B          0.00B           ~     (all equal)
IntSet-48                         0.00B          0.00B           ~     (all equal)
FloatAdd                          0.00B          0.00B           ~     (all equal)
FloatAdd-6                        0.00B          0.00B           ~     (all equal)
FloatAdd-48                       0.00B          0.00B           ~     (all equal)
FloatSet                          0.00B          0.00B           ~     (all equal)
FloatSet-6                        0.00B          0.00B           ~     (all equal)
FloatSet-48                       0.00B          0.00B           ~     (all equal)
MapSet                            0.00B         48.00B ± 0%     +Inf%  (p=0.000 n=8+8)
MapSet-6                          0.00B         48.00B ± 0%     +Inf%  (p=0.000 n=8+8)
MapSet-48                         0.00B         48.00B ± 0%     +Inf%  (p=0.000 n=8+8)
MapSetDifferent                   0.00B        192.00B ± 0%     +Inf%  (p=0.000 n=8+8)
MapSetDifferent-6                 0.00B        192.00B ± 0%     +Inf%  (p=0.000 n=8+8)
MapSetDifferent-48                0.00B        192.00B ± 0%     +Inf%  (p=0.000 n=8+8)
MapSetString                      0.00B         48.00B ± 0%     +Inf%  (p=0.000 n=8+8)
MapSetString-6                    0.00B         48.00B ± 0%     +Inf%  (p=0.000 n=8+8)
MapSetString-48                   0.00B         48.00B ± 0%     +Inf%  (p=0.000 n=8+8)
MapAddSame                         456B ± 0%      480B ± 0%    +5.26%  (p=0.000 n=8+8)
MapAddSame-6                       456B ± 0%      480B ± 0%    +5.26%  (p=0.000 n=8+8)
MapAddSame-48                      456B ± 0%      480B ± 0%    +5.26%  (p=0.000 n=8+8)
MapAddDifferent                    672B ± 0%     1088B ± 0%   +61.90%  (p=0.000 n=8+8)
MapAddDifferent-6                  672B ± 0%     1088B ± 0%   +61.90%  (p=0.000 n=8+8)
MapAddDifferent-48                 672B ± 0%     1088B ± 0%   +61.90%  (p=0.000 n=8+8)
MapAddSameSteadyState             0.00B          0.00B           ~     (all equal)
MapAddSameSteadyState-6           0.00B          0.00B           ~     (all equal)
MapAddSameSteadyState-48          0.00B          0.00B           ~     (all equal)
MapAddDifferentSteadyState        0.00B          0.00B           ~     (all equal)
MapAddDifferentSteadyState-6      0.00B          0.00B           ~     (all equal)
MapAddDifferentSteadyState-48     0.00B          0.00B           ~     (all equal)
RealworldExpvarUsage              0.00B          0.00B           ~     (all equal)
RealworldExpvarUsage-6            0.00B          0.00B           ~     (all equal)
RealworldExpvarUsage-48           0.00B          0.00B           ~     (all equal)

name                           old allocs/op  new allocs/op  delta
IntAdd                             0.00           0.00           ~     (all equal)
IntAdd-6                           0.00           0.00           ~     (all equal)
IntAdd-48                          0.00           0.00           ~     (all equal)
IntSet                             0.00           0.00           ~     (all equal)
IntSet-6                           0.00           0.00           ~     (all equal)
IntSet-48                          0.00           0.00           ~     (all equal)
FloatAdd                           0.00           0.00           ~     (all equal)
FloatAdd-6                         0.00           0.00           ~     (all equal)
FloatAdd-48                        0.00           0.00           ~     (all equal)
FloatSet                           0.00           0.00           ~     (all equal)
FloatSet-6                         0.00           0.00           ~     (all equal)
FloatSet-48                        0.00           0.00           ~     (all equal)
MapSet                             0.00           3.00 ± 0%     +Inf%  (p=0.000 n=8+8)
MapSet-6                           0.00           3.00 ± 0%     +Inf%  (p=0.000 n=8+8)
MapSet-48                          0.00           3.00 ± 0%     +Inf%  (p=0.000 n=8+8)
MapSetDifferent                    0.00          12.00 ± 0%     +Inf%  (p=0.000 n=8+8)
MapSetDifferent-6                  0.00          12.00 ± 0%     +Inf%  (p=0.000 n=8+8)
MapSetDifferent-48                 0.00          12.00 ± 0%     +Inf%  (p=0.000 n=8+8)
MapSetString                       0.00           3.00 ± 0%     +Inf%  (p=0.000 n=8+8)
MapSetString-6                     0.00           3.00 ± 0%     +Inf%  (p=0.000 n=8+8)
MapSetString-48                    0.00           3.00 ± 0%     +Inf%  (p=0.000 n=8+8)
MapAddSame                         6.00 ± 0%     11.00 ± 0%   +83.33%  (p=0.000 n=8+8)
MapAddSame-6                       6.00 ± 0%     11.00 ± 0%   +83.33%  (p=0.000 n=8+8)
MapAddSame-48                      6.00 ± 0%     11.00 ± 0%   +83.33%  (p=0.000 n=8+8)
MapAddDifferent                    14.0 ± 0%      31.0 ± 0%  +121.43%  (p=0.000 n=8+8)
MapAddDifferent-6                  14.0 ± 0%      31.0 ± 0%  +121.43%  (p=0.000 n=8+8)
MapAddDifferent-48                 14.0 ± 0%      31.0 ± 0%  +121.43%  (p=0.000 n=8+8)
MapAddSameSteadyState              0.00           0.00           ~     (all equal)
MapAddSameSteadyState-6            0.00           0.00           ~     (all equal)
MapAddSameSteadyState-48           0.00           0.00           ~     (all equal)
MapAddDifferentSteadyState         0.00           0.00           ~     (all equal)
MapAddDifferentSteadyState-6       0.00           0.00           ~     (all equal)
MapAddDifferentSteadyState-48      0.00           0.00           ~     (all equal)
RealworldExpvarUsage               0.00           0.00           ~     (all equal)
RealworldExpvarUsage-6             0.00           0.00           ~     (all equal)
RealworldExpvarUsage-48            0.00           0.00           ~     (all equal)

https://perf.golang.org/search?q=upload:20170427.1

Change-Id: I388b2e8a3cadb84fc1418af8acfc27338f799273
Reviewed-on: https://go-review.googlesource.com/41930
Run-TryBot: Bryan Mills <bcmills@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
expvar: add benchmark for (*Map).Set with per-goroutine keys 2017-03-10T19:09:48+00:00 Bryan C. Mills bcmills@google.com 2017-03-09T21:45:14+00:00 7e036521d505708a3e0d0b3d9bbe1e4853111211 Change-Id: I0fa68ca9812fe5e82ffb9d0b9598e95b47183eb8 Reviewed-on: https://go-review.googlesource.com/38011 Reviewed-by: Ian Lance Taylor <iant@golang.org> Run-TryBot: Ian Lance Taylor <iant@golang.org> TryBot-Result: Gobot Gobot <gobot@golang.org> 
Change-Id: I0fa68ca9812fe5e82ffb9d0b9598e95b47183eb8
Reviewed-on: https://go-review.googlesource.com/38011
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
expvar: add benchmarks for steady-state Map Add calls 2017-02-14T22:11:35+00:00 Bryan C. Mills bcmills@google.com 2017-02-14T06:00:49+00:00 7ffdb757758c086556e5eba277202d9d8940c2bd Add a benchmark for setting a String value, which we may want to treat differently from Int or Float due to the need to support Add methods for the latter. Update tests to use only the exported API instead of making (fragile) assumptions about unexported fields. The existing Map benchmarks construct a new Map for each iteration, which focuses the benchmark results on the initial allocation costs for the Map and its entries. This change adds variants of the benchmarks which use a long-lived map in order to measure steady-state performance for Map updates on existing keys. Updates #18177 Change-Id: I62c920991d17d5898c592446af382cd5c04c528a Reviewed-on: https://go-review.googlesource.com/36959 Reviewed-by: Ian Lance Taylor <iant@golang.org> 
Add a benchmark for setting a String value, which we may
want to treat differently from Int or Float due to the need to support
Add methods for the latter.

Update tests to use only the exported API instead of making (fragile)
assumptions about unexported fields.

The existing Map benchmarks construct a new Map for each iteration, which
focuses the benchmark results on the initial allocation costs for the
Map and its entries. This change adds variants of the benchmarks which
use a long-lived map in order to measure steady-state performance for
Map updates on existing keys.

Updates #18177

Change-Id: I62c920991d17d5898c592446af382cd5c04c528a
Reviewed-on: https://go-review.googlesource.com/36959
Reviewed-by: Ian Lance Taylor <iant@golang.org>
expvar: make BenchmarkAdd{Same,Different} comparable to 1.8 2017-02-10T20:08:14+00:00 Bryan C. Mills bcmills@google.com 2017-02-10T19:46:22+00:00 aa1538799601bdbc881f2ad3133184377b7e7aca bradfitz noted in change 36717 that the new behavior was no longer comparable with the old. This change restores comparable behavior for -cpu=1. BenchmarkMapAddSame 909 909 +0.00% BenchmarkMapAddSame-6 1309 262 -79.98% BenchmarkMapAddDifferent 2856 3030 +6.09% BenchmarkMapAddDifferent-6 3803 581 -84.72% updates #18177 Change-Id: Ifaff5a1f48be92002d86c296220313b7efdc81d6 Reviewed-on: https://go-review.googlesource.com/36723 Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org> Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org> TryBot-Result: Gobot Gobot <gobot@golang.org> 
bradfitz noted in change 36717 that the new behavior was no longer
comparable with the old.  This change restores comparable behavior
for -cpu=1.

BenchmarkMapAddSame                 909           909           +0.00%
BenchmarkMapAddSame-6               1309          262           -79.98%
BenchmarkMapAddDifferent            2856          3030          +6.09%
BenchmarkMapAddDifferent-6          3803          581           -84.72%

updates #18177

Change-Id: Ifaff5a1f48be92002d86c296220313b7efdc81d6
Reviewed-on: https://go-review.googlesource.com/36723
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
expvar: parallelize BenchmarkMapAdd{Same,Different} 2017-02-10T17:37:14+00:00 Bryan C. Mills bcmills@google.com 2017-02-09T23:39:16+00:00 39651bb50bc0e1038e77e63baa37729bc4676e8a The other expvar tests are already parallelized, and this will help to measure the impact of potential implementations for #18177. updates #18177 Change-Id: I0f4f1a16a0285556cbcc8339855b6459af412675 Reviewed-on: https://go-review.googlesource.com/36717 Reviewed-by: Russ Cox <rsc@golang.org> 
The other expvar tests are already parallelized, and this will help to
measure the impact of potential implementations for #18177.

updates #18177

Change-Id: I0f4f1a16a0285556cbcc8339855b6459af412675
Reviewed-on: https://go-review.googlesource.com/36717
Reviewed-by: Russ Cox <rsc@golang.org>
expvar: add Value methods 2016-10-13T21:39:03+00:00 Filippo Valsorda hi@filippo.io 2016-10-13T16:56:04+00:00 714318be882d1974ec624272c8d905256d8a5932 Closes #15815 Change-Id: I08154dbff416198cf7787e446b1e00e62c03a972 Reviewed-on: https://go-review.googlesource.com/30917 Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org> Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org> TryBot-Result: Gobot Gobot <gobot@golang.org> 
Closes #15815

Change-Id: I08154dbff416198cf7787e446b1e00e62c03a972
Reviewed-on: https://go-review.googlesource.com/30917
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
expvar: export http.Handler 2016-09-25T23:34:28+00:00 Anders Pearson anders@columbia.edu 2016-07-03T13:22:06+00:00 6ba5b32922c438a608a11561100a8a80abf0fd3a Add a method to expose the handler to allow it to be installed at a non-standard location or used with a different ServeMux. fixes #15030 Change-Id: If778ad6fcc200f124a05c0a493511e364fca6078 Reviewed-on: https://go-review.googlesource.com/24722 Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org> Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org> TryBot-Result: Gobot Gobot <gobot@golang.org> 
Add a method to expose the handler to allow it to be installed at a
non-standard location or used with a different ServeMux.

fixes #15030

Change-Id: If778ad6fcc200f124a05c0a493511e364fca6078
Reviewed-on: https://go-review.googlesource.com/24722
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
expvar: slightly expand documentation for Var's String method 2016-05-19T04:20:47+00:00 Scott Bell scott@sctsm.com 2016-05-19T01:44:46+00:00 2a12035f8ec18f0a577853fda78faf2826397131 Fixes #15088. Change-Id: I7727829a4062e15c0e5e3beff4d0bfc1fa327b0f Reviewed-on: https://go-review.googlesource.com/23232 Reviewed-by: Andrew Gerrand <adg@golang.org> Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org> 
Fixes #15088.

Change-Id: I7727829a4062e15c0e5e3beff4d0bfc1fa327b0f
Reviewed-on: https://go-review.googlesource.com/23232
Reviewed-by: Andrew Gerrand <adg@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
expvar: Ensure strings are written as valid JSON. 2016-04-06T03:52:39+00:00 David Symonds dsymonds@golang.org 2016-04-06T01:53:26+00:00 6f2a8810b01d6332d35c9b3e3e64c13f60d31776 Change-Id: I5147dbf4e85cf42cd1f32c57861e4c16d9dbd049 Reviewed-on: https://go-review.googlesource.com/21529 Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org> Reviewed-by: Andrew Gerrand <adg@golang.org> 
Change-Id: I5147dbf4e85cf42cd1f32c57861e4c16d9dbd049
Reviewed-on: https://go-review.googlesource.com/21529
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Andrew Gerrand <adg@golang.org>