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Date: Wed, 29 Apr 2009 15:08:34 +0900 (JST) From: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> To: balbir@...ux.vnet.ibm.com Cc: kosaki.motohiro@...fujitsu.com, LKML <linux-kernel@...r.kernel.org>, Bharata B Rao <bharata@...ux.vnet.ibm.com>, Balaji Rao <balajirrao@...il.com>, Dhaval Giani <dhaval@...ux.vnet.ibm.com>, KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>, Peter Zijlstra <a.p.zijlstra@...llo.nl>, Ingo Molnar <mingo@...e.hu>, Martin Schwidefsky <schwidefsky@...ibm.com>, seto.hidetoshi@...fujitsu.com Subject: Re: [PATCH] cpuacct: VIRT_CPU_ACCOUNTING don't prevent percpu cputime count > > > This will make the end result very off the real value due to large > > > batch value per cpu. If we are going to go this route, we should > > > probably consider using __percpu_counter_sum so that the batch value > > > does not show data that is way off. > > > > No problem. > > > > end-user don't see cputime itself. they see converted time. > > cpuacct_stats_show() use cputime64_to_clock_t. it mean > > the value less than 10msec don't display. > > > > Yes, I know, I reviewed Bharata's patch and suggested converting to > clock_t for consistency with other metrics. Oh, sorry. I didn't know this. > > -------------------------------------------------------- > > static int cpuacct_stats_show(struct cgroup *cgrp, struct cftype *cft, > > struct cgroup_map_cb *cb) > > { > > struct cpuacct *ca = cgroup_ca(cgrp); > > int i; > > > > for (i = 0; i < CPUACCT_STAT_NSTATS; i++) { > > s64 val = percpu_counter_read(&ca->cpustat[i]); > > My point is, this should probably be percpu_counter_sum(), but that > can be expensive and we were willing to tollerate some inaccuracy due > to batch value, I think your patch adds to the inaccuracy even more, > even though it fixes a genuine problem. Not expensive. cpuacct_stats_show() is only called when reading stat file. it definitely slow-path. I think we can use percpu_counter_sum(). However, I doubt its worth. before my patch: VIRT_CPU_ACCOUNTING=y: accuracy but slow VIRT_CPU_ACCOUNTING=n: inaccuracy few tick but fast my patch VIRT_CPU_ACCOUNTING=y: inaccuracy few tick but fast VIRT_CPU_ACCOUNTING=n: inaccuracy few tick but fast if my inaccuracy is wrong, current code is also crap when VIRT_CPU_ACCOUNTING=n. I only make const accuracy to VIRT_CPU_ACCOUNTING=y and n. Thought? Although you still think percpu_counter_sum() is better, I can do it. > > > > val = cputime64_to_clock_t(val); > > cb->fill(cb, cpuacct_stat_desc[i], val); > > } > > return 0; > > } > > -------------------------------------------------------- -- 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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