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CPUTimer: switch to clock_gettime #4667

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merged 1 commit into from Jul 17, 2014
Merged

CPUTimer: switch to clock_gettime #4667

merged 1 commit into from Jul 17, 2014

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fwyzard
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@fwyzard fwyzard commented Jul 16, 2014

  • switch from gettimeofday/getrusage to clock_gettime, with the same speed but better accuracy (at least on x86_64 Linux)
  • switch from clock_gettime(CLOCK_REALTIME) to clock_gettime(CLOCK_MONOTONIC), with a very similar performance, but conceptually more sound

@cmsbuild
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A new Pull Request was created by @fwyzard (Andrea Bocci) for CMSSW_7_2_X.

CPUTimer: switch to clock_gettime

It involves the following packages:

FWCore/Utilities

@cmsbuild, @Degano, @Dr15Jones, @ktf, @nclopezo can you please review it and eventually sign? Thanks.
@wddgit, @wmtan this is something you requested to watch as well.
You can sign-off by replying to this message having '+1' in the first line of your reply.
You can reject by replying to this message having '-1' in the first line of your reply.

@fwyzard
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fwyzard commented Jul 16, 2014

Here is the speed and resolution of the real-time and cpu-time clocks used by CPUTimer, as measured by $CMSSW_RELEASE_BASE/test/$SCRAM_ARCH/testChrono .

CMSSW 7.2.x on lxplus (SLC6, virtual machine)

Linux 2.6.32-431.17.1.el6.x86_64 x86_64
glibc version: 2.12
clock source: kvm-clock
For each timer the resolution reported is the MINIMUM (MEDIAN) (MEAN +/- its STDDEV) of the increments measured during the test.

Performance of clock_gettime(CLOCK_REALTIME)
Average time per call: 328.8 ns
Clock tick period: 1.0 ns
Measured resolution: 312.0 ns (median: 319.0 ns) (sigma: 351.9 ns) (average: 328.8 +/- 0.4 ns)

Performance of clock_gettime(CLOCK_MONOTONIC)
Average time per call: 324.7 ns
Clock tick period: 1.0 ns
Measured resolution: 311.0 ns (median: 317.0 ns) (sigma: 396.4 ns) (average: 324.7 +/- 0.4 ns)

Performance of clock_gettime(CLOCK_PROCESS_CPUTIME_ID)
Average time per call: 473.2 ns
Clock tick period: 1.0 ns
Measured resolution: 455.0 ns (median: 461.0 ns) (sigma: 367.9 ns) (average: 472.7 +/- 0.4 ns)

Performance of gettimeofday()
Average time per call: 351.1 ns
Clock tick period: 1000.0 ns
Measured resolution: 1000.0 ns (median: 1000.0 ns) (sigma: 519.5 ns) (average: 1020.9 +/- 0.9 ns)

Performance of getrusage(RUSAGE_SELF)
Average time per call: 466.9 ns
Clock tick period: 1000.0 ns
Measured resolution: 999000.0 ns (median: 1000000.0 ns) (sigma: 359.4 ns) (average: 999848.0 +/- 16.6 ns)

CMSSW 7.1.1 on an HLT machine (SLC6, Sandy Bridge Xeon)

Linux 2.6.32-358.11.1.el6.x86_64 x86_64
glibc version: 2.12
clock source: tsc
For each timer the resolution reported is the MINIMUM (MEDIAN) (MEAN +/- its STDDEV) of the increments measured during the test.

Performance of clock_gettime(CLOCK_REALTIME)
Average time per call: 28.7 ns
Clock tick period: 1.0 ns
Measured resolution: 26.0 ns (median: 29.0 ns) (sigma: 10.5 ns) (average: 28.7 +/- 0.1 ns)

Performance of clock_gettime(CLOCK_MONOTONIC)
Average time per call: 30.0 ns
Clock tick period: 1.0 ns
Measured resolution: 26.0 ns (median: 30.0 ns) (sigma: 16.4 ns) (average: 30.0 +/- 0.1 ns)

Performance of clock_gettime(CLOCK_PROCESS_CPUTIME_ID)
Average time per call: 168.5 ns
Clock tick period: 1.0 ns
Measured resolution: 160.0 ns (median: 168.0 ns) (sigma: 19.2 ns) (average: 168.1 +/- 0.1 ns)

Performance of gettimeofday()
Average time per call: 30.3 ns
Clock tick period: 1000.0 ns
Measured resolution: 1000.0 ns (median: 1000.0 ns) (sigma: 50.5 ns) (average: 1001.3 +/- 0.3 ns)

Performance of getrusage(RUSAGE_SELF)
Average time per call: 187.6 ns
Clock tick period: 1000.0 ns
Measured resolution: 999000.0 ns (median: 1000000.0 ns) (sigma: 357.8 ns) (average: 999850.3 +/- 26.2 ns)

@Dr15Jones
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+1

@cmsbuild
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This pull request is fully signed and it will be integrated in one of the next CMSSW_7_2_X IBs unless changes or unless it breaks tests.

@cmsbuild
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-1

Tested at: cc3b07d
I ran the usual tests and I found errors in the following unit tests:

---> test TestFWCoreServicesDriver had ERRORS

you can see the results of the tests here:
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-4667/353/summary.html

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This pull request is fully signed and it will be integrated in one of the next CMSSW_7_2_X IBs unless changes (but tests are reportedly failing).

@fwyzard
CPUTimer: switch to clock_gettime
a7de539 
  - switch from gettimeofday/getrusage to clock_gettime,
    with the same speed but better accuracy (at least on x86_64 Linux)
  - switch from clock_gettime(CLOCK_REALTIME) to clock_gettime(CLOCK_MONOTONIC)
    with a very similar performance, but conceptually more sound
@cmsbuild
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Pull request #4667 was updated. @cmsbuild, @Degano, @Dr15Jones, @ktf, @nclopezo can you please check and sign again.

@fwyzard
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fwyzard commented Jul 16, 2014

Fixed (and tested) - sorry about that.

@Dr15Jones
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+1
On vacation

@cmsbuild
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This pull request is fully signed and it will be integrated in one of the next CMSSW_7_2_X IBs unless changes or unless it breaks tests.

@cmsbuild
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Comparison is ready
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-4667/353/summary.html

@cmsbuild
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This pull request is fully signed and it will be integrated in one of the next CMSSW_7_2_X IBs unless changes or unless it breaks tests.

@cmsbuild
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+1
Tested at: a7de539
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-4667/357/summary.html

@cmsbuild
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This pull request is fully signed and it will be integrated in one of the next CMSSW_7_2_X IBs unless changes (tests are also fine).

ktf added a commit that referenced this pull request Jul 17, 2014
@ktf
Merge pull request #4667 from fwyzard/CPUTimer_use_clock_gettime
3bee217 
CPUTimer: switch to clock_gettime
@ktf ktf merged commit 3bee217 into cms-sw:CMSSW_7_2_X Jul 17, 2014
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Comparison is ready
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-4667/357/summary.html

@fwyzard fwyzard deleted the CPUTimer_use_clock_gettime branch August 29, 2014 14:47
@smuzaffar smuzaffar mentioned this pull request Oct 24, 2023
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