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Message-Id: <1400288204-414-1-git-send-email-john.stultz@linaro.org> Date: Fri, 16 May 2014 17:56:41 -0700 From: John Stultz <john.stultz@...aro.org> To: LKML <linux-kernel@...r.kernel.org> Cc: John Stultz <john.stultz@...aro.org>, Miroslav Lichvar <mlichvar@...hat.com>, Richard Cochran <richardcochran@...il.com>, Prarit Bhargava <prarit@...hat.com> Subject: [PATCH 0/3] timekeeping: Improved NOHZ frequency steering (v2) I managed to find some time to further work on the next iteration here. This patch set, based on ideas from Miroslav, tries to improve the ntp freq steering when using NOHZ. Rather then just doing error proportional correction, this patchset splits the logic to two steps: frequency correction and error correction. By doing this, we are able to cap the rate of the error correction, so it is small and we avoid the strong over-corrections seen with the previous implementation when NOHZ was enabled. This version of the patch set corrects a few issues Miroslav pointed out, as well as adapts his approach almost completely for the last patch. This pulls the results in to be very close to his original patch. I'm not 100% sure we need the last patch in this series, as it has additional computational cost and testing on real hardware has shown NOHZ=y performance matching NOHZ=n with a earlier version of just the first patch: https://lkml.org/lkml/2014/1/13/501 (though admittedly, the patch has changed since Richard's testing, so the results are a bit stale). Below are some of the simulator results comparing this patchset to vanilla and Miroslav's original patch. Vanilla 3.15-rc --------------- $ ./tk_test -t 500 -n 4000 samples: 1-500 reg: 1-500 slope: 1.00 dev: 2252427.1 max: 9614317.1 freq: -99.94417 samples: 501-1000 reg: 501-1000 slope: 1.00 dev: 1426381.1 max: 7957313.5 freq: -100.23188 samples: 1001-1500 reg: 1001-1500 slope: 1.00 dev: 1146520.7 max: 7795769.4 freq: -99.96096 samples: 1501-2000 reg: 1501-2000 slope: 1.00 dev: 942903.0 max: 7091089.3 freq: -100.24301 samples: 2001-2500 reg: 2001-2500 slope: 1.00 dev: 927526.2 max: 6688226.0 freq: -99.74349 samples: 2501-3000 reg: 2501-3000 slope: 1.00 dev: 843482.1 max: 10259091.7 freq: -100.01513 samples: 3001-3500 reg: 3001-3500 slope: 1.00 dev: 935390.6 max: 9055331.8 freq: -99.74709 samples: 3501-4000 reg: 3501-4000 slope: 1.00 dev: 760640.7 max: 8755998.4 freq: -99.75966 $ ./test1.sh freq10 fre100 dev max nohz on 38.38368 2.72579 1468940.9 9846788.2 nohz off 3.89181 0.10436 0.2 0.6 Miroslav's original patch: -------------------------- $ ./tk_test -t 500 -n 4000 samples: 1-500 reg: 1-500 slope: 1.00 dev: 115.5 max: 300.1 freq: -100.00004 samples: 501-1000 reg: 501-1000 slope: 1.00 dev: 73.7 max: 289.6 freq: -100.00003 samples: 1001-1500 reg: 1001-1500 slope: 1.00 dev: 59.7 max: 283.9 freq: -100.00001 samples: 1501-2000 reg: 1501-2000 slope: 1.00 dev: 50.6 max: 291.6 freq: -100.00000 samples: 2001-2500 reg: 2001-2500 slope: 1.00 dev: 48.6 max: 285.7 freq: -100.00002 samples: 2501-3000 reg: 2501-3000 slope: 1.00 dev: 44.8 max: 293.5 freq: -99.99993 samples: 3001-3500 reg: 3001-3500 slope: 1.00 dev: 40.5 max: 303.8 freq: -99.99996 samples: 3501-4000 reg: 3501-4000 slope: 1.00 dev: 37.6 max: 288.5 freq: -99.99997 $ ./test1.sh freq10 freq100 dev max nohz on 0.00601 0.00028 74.0 279.4 nohz off 0.05867 0.00204 0.2 0.6 This patchset: -------------- $ ./tk_test -t 500 -n 4000 samples: 1-500 reg: 1-500 slope: 1.00 dev: 111.0 max: 276.4 freq: -100.00000 samples: 501-1000 reg: 501-1000 slope: 1.00 dev: 76.5 max: 286.7 freq: -99.99998 samples: 1001-1500 reg: 1001-1500 slope: 1.00 dev: 59.3 max: 291.8 freq: -100.00003 samples: 1501-2000 reg: 1501-2000 slope: 1.00 dev: 51.2 max: 290.7 freq: -100.00001 samples: 2001-2500 reg: 2001-2500 slope: 1.00 dev: 48.0 max: 275.9 freq: -100.00002 samples: 2501-3000 reg: 2501-3000 slope: 1.00 dev: 44.8 max: 293.2 freq: -99.99993 samples: 3001-3500 reg: 3001-3500 slope: 1.00 dev: 40.1 max: 300.4 freq: -99.99998 samples: 3501-4000 reg: 3501-4000 slope: 1.00 dev: 37.6 max: 285.7 freq: -99.99999 $ ./test1.sh freq10 freq100 dev max nohz on 0.00582 0.00033 74.1 279.9 nohz off 0.06275 0.06440 0.4 1.4 Again, many many thanks to Miroslav for pointing out this issue, providing the simulator and initial patches, as well as helping to point out problems with my rework of his change. Comments, and feedback and testing (particularly on 32bit systems, and systems like powerpc) would be greatly appreciated! thanks -john Cc: Miroslav Lichvar <mlichvar@...hat.com> Cc: Richard Cochran <richardcochran@...il.com> Cc: Prarit Bhargava <prarit@...hat.com> John Stultz (3): [RFC] timekeeping: Rework frequency adjustments to work better w/ nohz [RFC] timekeeping: Use cached ntp_tick_length when accumulating error [RFC] timekeeping: Calculate freq adjustment directly include/linux/timekeeper_internal.h | 12 +++ kernel/time/timekeeping.c | 175 ++++++++++++++---------------------- 2 files changed, 77 insertions(+), 110 deletions(-) -- 1.9.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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