linux-kernel - Re: [PATCH 1/5] vmstat: Implement refresh_vm

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Date:	Thu, 07 Jun 2012 23:17:28 -0400
From:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
To:	Anton Vorontsov <anton.vorontsov@...aro.org>
CC:	Pekka Enberg <penberg@...nel.org>,
	Leonid Moiseichuk <leonid.moiseichuk@...ia.com>,
	KOSAKI Motohiro <kosaki.motohiro@...il.com>,
	Minchan Kim <minchan@...nel.org>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
	John Stultz <john.stultz@...aro.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, linaro-kernel@...ts.linaro.org,
	patches@...aro.org, kernel-team@...roid.com
Subject: Re: [PATCH 1/5] vmstat: Implement refresh_vm_stats()

(6/1/12 8:24 AM), Anton Vorontsov wrote:
> This function forcibly flushes per-cpu vmstat diff counters to the
> global counters.
> 
> Note that we don't try to flush percpu pagesets, the pcp will be
> still flushed once per 3 seconds.
> 
> Signed-off-by: Anton Vorontsov<anton.vorontsov@...aro.org>

No.

This is insane. Your patch improved vmevent accuracy a _bit_. But instead of,
decrease a performance of large systems. That's no good deal. 99% user never
uses vmevent.

MOREOVER, this patch don't solve vmevent accuracy issue AT ALL. because of,
a second is enough big to make large inaccuracy. Modern cpus are fast. Guys,
the fact is, user land monitor can't use implicit batch likes vmstat. That's
a reason why perf don't use vmstat. I suggest you see perf APIs. It may bring
you good inspiration.

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