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Date: Thu, 04 Sep 2008 13:06:00 +0200 From: Peter Zijlstra <a.p.zijlstra@...llo.nl> To: Lin Ming <ming.m.lin@...el.com> Cc: linux-kernel <linux-kernel@...r.kernel.org>, "Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>, mingo <mingo@...e.hu>, Gregory Haskins <ghaskins@...ell.com> Subject: Re: oltp ~10% regression with 2.6.27-rc5 on stoakley machine On Thu, 2008-09-04 at 18:52 +0800, Lin Ming wrote: > On Thu, 2008-09-04 at 11:03 +0200, Peter Zijlstra wrote: > > On Thu, 2008-09-04 at 16:51 +0800, Lin Ming wrote: > > > Comparing with 2.6.27-rc4, oltp has ~10% regression with 2.6.27-rc5 on > > > 8-core stoakley machine. > > > > > > Run oltp with 8 threads 120 seconds, vmstat shows much more idle time, about ~30% > > > > > > procs -----------memory---------- ---swap-- -----io---- --system-- -----cpu------ > > > r b swpd free buff cache si so bi bo in cs us sy id wa st > > > 10 0 0 7822824 42240 123740 0 0 312 47 442 1613 3 2 88 6 0 > > > 9 0 0 7822312 42240 123764 0 0 0 16 26691 232566 56 14 30 0 0 > > > 13 0 0 7821940 42240 123764 0 0 0 16 26661 228689 54 14 32 0 0 > > > 8 0 0 7821320 42240 123764 0 0 0 16 31508 263765 61 17 23 0 0 > > > 12 0 0 7820948 42240 123764 0 0 16 16 28666 242402 57 15 28 0 0 > > > 9 0 0 7820584 42240 123780 0 0 0 16 27107 230804 56 14 30 0 0 > > > 10 0 0 7819964 42240 123796 0 0 16 612 27599 244037 55 16 29 0 0 > > > 11 0 0 7819356 42240 123796 0 0 0 64 23540 209713 51 13 36 0 0 > > > 10 0 0 7819212 42240 123796 0 0 0 32 25674 224205 54 13 32 0 0 > > > 10 0 0 7818716 42240 123796 0 0 0 20 30106 257161 59 16 25 0 0 > > > 7 0 0 7818468 42240 123796 0 0 0 16 28356 241551 57 14 29 0 0 > > > 10 0 0 7818096 42240 123796 0 0 0 16 39174 273656 64 16 20 0 0 > > > 12 0 0 7817724 42240 123796 0 0 0 20 39688 276936 63 16 20 0 0 > > > 11 0 0 7817352 42240 123796 0 0 0 16 42543 285192 66 16 18 0 0 > > > 9 0 0 7817352 42240 123796 0 0 0 16 37083 259830 62 14 24 0 0 > > > 8 0 0 7817104 42240 123796 0 0 0 16 37450 259160 61 15 23 0 0 > > > 10 0 0 7816516 42240 123796 0 0 0 64 37425 261870 61 16 23 0 0 > > > 11 0 0 7815896 42240 123812 0 0 16 16 41558 279320 66 16 18 0 0 > > > 9 0 0 7815648 42240 123812 0 0 0 16 34017 235741 59 14 28 0 0 > > > 10 0 0 7815152 42240 123812 0 0 0 16 35642 248888 60 14 26 0 0 > > > 9 0 0 7814532 42240 123812 0 0 0 16 38517 263220 63 15 22 0 0 > > > 9 0 0 7814160 42240 123812 0 0 0 20 35965 246487 61 14 25 0 0 > > > 10 0 0 7814036 42240 123812 0 0 0 16 33852 236313 59 13 28 0 0 > > > 11 0 0 7813664 42240 123812 0 0 0 16 34958 244819 59 14 27 0 0 > > > 10 0 0 7813416 42240 123812 0 0 0 16 26106 202062 53 10 37 0 0 > > > 10 0 0 7812672 42240 123812 0 0 0 16 31174 222714 56 12 32 0 0 > > > 9 0 0 7812300 42240 123812 0 0 0 276 25089 196813 52 11 38 0 0 > > > 9 0 0 7812060 42240 123812 0 0 0 16 31877 228004 57 12 31 0 0 > > > > > > > > > > > > Bisect located below patch, > > > after reverted this patch the regression disappear. > > > > > > commit 354879bb977e06695993435745f06a0f6d39ce2b > > > Author: Peter Zijlstra <a.p.zijlstra@...llo.nl> > > > Date: Mon Aug 25 17:15:34 2008 +0200 > > > > > > sched_clock: fix cpu_clock() > > > > > > This patch fixes 3 issues: > > > > > > a) it removes the dependency on jiffies, because jiffies are > > > incremented > > > by a single CPU, and the tick is not synchronized between CPUs. > > > Therefore > > > relying on it to calculate a window to clip whacky TSC values > > > doesn't work > > > as it can drift around. > > > > > > So instead use [GTOD, GTOD+TICK_NSEC) as the window. > > > > > > b) __update_sched_clock() did (roughly speaking): > > > > > > delta = sched_clock() - scd->tick_raw; > > > clock += delta; > > > > > > Which gives exponential growth, instead of linear. > > > > > > c) allows the sched_clock_cpu() value to warp the u64 without > > > breaking. > > > > > > the results are more reliable sched_clock() deltas: > > > > Thats bizarre... that just indicates the better clock, which should give > > better (read fairer) scheduling hurts your workload. > > > > Is there anything I can run to see if we can fix the scheduler perhaps? > > I observed schedstats of sysbench, there's more > "nr_failed_migrations_hot" > > 2.6.27-rc4: se.nr_failed_migrations_hot 11 > 2.6.27-rc5: se.nr_failed_migrations_hot 95 > > task migration failed because of task_hot, the system is un-balanced? Ah, that makes sense, a more accurate clock could indeed make more tasks hot. Can you try fiddling with: /proc/sys/kernel/sched_migration_cost ? Also, we used to have some auto-tuning in there, which dissapeared some time ago, gregory brought it back to live recently, perhaps he likes to share? :-) -- 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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