linux-kernel - Re: [PATCH v5 8/8] mm: add vmstat counters for tracking PCP drains

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Message-ID: <CAOtvUMc259XZ5BdOqys3Kbv_u=Qa0matnuFyGrJhMPLtRKKkUA@mail.gmail.com>
Date:	Tue, 3 Jan 2012 21:00:17 +0200
From:	Gilad Ben-Yossef <gilad@...yossef.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
Cc:	linux-kernel@...r.kernel.org, Christoph Lameter <cl@...ux.com>,
	Chris Metcalf <cmetcalf@...era.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Frederic Weisbecker <fweisbec@...il.com>, linux-mm@...ck.org,
	Pekka Enberg <penberg@...nel.org>,
	Matt Mackall <mpm@...enic.com>,
	Sasha Levin <levinsasha928@...il.com>,
	Rik van Riel <riel@...hat.com>,
	Andi Kleen <andi@...stfloor.org>, Mel Gorman <mel@....ul.ie>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Avi Kivity <avi@...hat.com>
Subject: Re: [PATCH v5 8/8] mm: add vmstat counters for tracking PCP drains

2012/1/3 KOSAKI Motohiro <kosaki.motohiro@...il.com>:
> (1/2/12 5:24 AM), Gilad Ben-Yossef wrote:
>> This patch introduces two new vmstat counters: pcp_global_drain
>> that counts the number of times a per-cpu pages global drain was
>> requested and pcp_global_ipi_saved that counts the number of times
>> the number of CPUs with per-cpu pages in any zone were less then
>> 1/2 of the number of online CPUs.
>>
>> The patch purpose is to show the usefulness of only sending an IPI
>> asking to drain per-cpu pages to CPUs that actually have them
>> instead of a blind global IPI. It is probably not useful by itself.
...

             }
>>       on_each_cpu_mask(cpus_with_pcps, drain_local_pages, NULL, 1);
>> +
>> +     count_vm_event(PCP_GLOBAL_DRAIN);
>> +     if (cpumask_weight(cpus_with_pcps)<  (cpumask_weight(cpu_online_mask) / 2))
>> +             count_vm_event(PCP_GLOBAL_IPI_SAVED);
>
> NAK.
>
> PCP_GLOBAL_IPI_SAVED is only useful at development phase. I can't
> imagine normal admins use it.

As the description explains, the purpose of the patch is to show why i
claim the previous
patch is useful. I did not meant it to be applied to mainline. My
apologies for not
stating this more clearly. I agree it is not useful for an admin,
although perhaps PCP_GLOBAL_DRAIN
alone might - I am not sure?

Gilad



-- 
Gilad Ben-Yossef
Chief Coffee Drinker
gilad@...yossef.com
Israel Cell: +972-52-8260388
US Cell: +1-973-8260388
http://benyossef.com

"Unfortunately, cache misses are an equal opportunity pain provider."
-- Mike Galbraith, LKML
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