linux-kernel - Re: [patch V3] percpu_counter: scalability works

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Date:	Tue, 17 May 2011 11:45:41 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Shaohua Li <shaohua.li@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"cl@...ux.com" <cl@...ux.com>,
	"npiggin@...nel.dk" <npiggin@...nel.dk>
Subject: Re: [patch V3] percpu_counter: scalability works

Le mardi 17 mai 2011 à 11:11 +0200, Tejun Heo a écrit :

> I'm completely fine with #1.  I'm not that crazy but I don't really
> want to take #2 - that makes the whole _sum() interface almost
> pointless.  

Hi Tejun

_sum() is a bit more precise than percpu_counter_read(), but to make it
really precise, we means we have to stop concurrent activities, and we
never did in previous/current implementation.

We could add this (as Shaohua and myself tried in various patches)
later, if needed, but nowhere in kernel we currently need that.

Even /proc/meminfo doesnt call _sum(&vm_committed_as) but the lazy
percpu_counter_read_positive() function...

Reammy _sum() gives a good approximation of the counter, more precise
because of the percpu s32 folding, but no guarantee of deviation.

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