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Date: Mon, 6 Apr 2009 12:30:26 +0900 (JST) From: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> To: linux-kernel@...r.kernel.org Cc: kosaki.motohiro@...fujitsu.com, anton@...ba.org, linux-mm <linux-mm@...ck.org>, Andrew Morton <akpm@...ux-foundation.org> Subject: Re: + mm-align-vmstat_works-timer.patch added to -mm tree (swich to lkml and linux-mm) Hi Anton, Do you have any mesurement data? Honestly, I made the same patch few week ago. but I found two problems. 1) work queue tracer (in -tip) reported it isn't proper rounded. The fact is, schedule_delayed_work(work, round_jiffies_relative()) is a bit ill. it mean - round_jiffies_relative() calculate rounded-time - jiffies - schedule_delayed_work() calculate argument + jiffies it assume no jiffies change at above two place. IOW it assume non preempt kernel. 2) > - schedule_delayed_work_on(cpu, vmstat_work, HZ + cpu); > + schedule_delayed_work_on(cpu, vmstat_work, > + __round_jiffies_relative(HZ, cpu)); isn't same meaning. vmstat_work mean to move per-cpu stastics to global stastics. Then, (HZ + cpu) mean to avoid to touch the same global variable at the same time. Oh well, this patch have performance regression risk on _very_ big server. (perhaps, only sgi?) but I agree vmstat_work is one of most work queue heavy user. For power consumption view, it isn't proper behavior. I still think improving another way. > > The patch titled > mm: align vmstat_work's timer > has been added to the -mm tree. Its filename is > mm-align-vmstat_works-timer.patch > > Before you just go and hit "reply", please: > a) Consider who else should be cc'ed > b) Prefer to cc a suitable mailing list as well > c) Ideally: find the original patch on the mailing list and do a > reply-to-all to that, adding suitable additional cc's > > *** Remember to use Documentation/SubmitChecklist when testing your code *** > > See http://userweb.kernel.org/~akpm/stuff/added-to-mm.txt to find > out what to do about this > > The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/ > > ------------------------------------------------------ > Subject: mm: align vmstat_work's timer > From: Anton Blanchard <anton@...ba.org> > > Even though vmstat_work is marked deferrable, there are still benefits to > aligning it. For certain applications we want to keep OS jitter as low as > possible and aligning timers and work so they occur together can reduce > their overall impact. > > Signed-off-by: Anton Blanchard <anton@...ba.org> > Signed-off-by: Andrew Morton <akpm@...ux-foundation.org> > --- > > mm/vmstat.c | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff -puN mm/vmstat.c~mm-align-vmstat_works-timer mm/vmstat.c > --- a/mm/vmstat.c~mm-align-vmstat_works-timer > +++ a/mm/vmstat.c > @@ -984,7 +984,7 @@ static void vmstat_update(struct work_st > { > refresh_cpu_vm_stats(smp_processor_id()); > schedule_delayed_work(&__get_cpu_var(vmstat_work), > - sysctl_stat_interval); > + round_jiffies_relative(sysctl_stat_interval)); > } > > static void __cpuinit start_cpu_timer(int cpu) > @@ -992,7 +992,8 @@ static void __cpuinit start_cpu_timer(in > struct delayed_work *vmstat_work = &per_cpu(vmstat_work, cpu); > > INIT_DELAYED_WORK_DEFERRABLE(vmstat_work, vmstat_update); > - schedule_delayed_work_on(cpu, vmstat_work, HZ + cpu); > + schedule_delayed_work_on(cpu, vmstat_work, > + __round_jiffies_relative(HZ, cpu)); > } > > /* > _ > > Patches currently in -mm which might be from anton@...ba.org are > > origin.patch > mm-align-vmstat_works-timer.patch > random-align-rekey_works-timer.patch > sunrpc-align-cache_clean-works-timer.patch > > -- > To unsubscribe from this list: send the line "unsubscribe mm-commits" in > the body of a message to majordomo@...r.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html -- 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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