linux-kernel - Re: [PATCH] percpu_counter : add percpu_counter_add

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Date:	Thu, 21 Oct 2010 18:10:13 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	Eric Dumazet <eric.dumazet@...il.com>,
	Nick Piggin <npiggin@...nel.dk>,
	Dave Chinner <david@...morbit.com>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] percpu_counter : add percpu_counter_add_fast()

On Thu, 21 Oct 2010, Andrew Morton wrote:

> That isn't actually what I was suggesting.  I was suggesting the use of
> an inlined, this_cpu_add()-using percpu_counter_add() variant which
> still does the batched spilling into ->count.  IOW, just speed up the
> current implementation along the lines of
>
> {
> 	val = this_cpu_add_return(*fbc->counters, amount);

this_cpu_add_return() is not in the kernel but could be realized using a
variant offshoot of cmpxchg_local. I had something like that initially but
omitted it since there was no use case.

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