linux-kernel - Re: [patch 05/41] cpu alloc: Percpu

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Date:	Fri, 30 May 2008 10:54:01 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	Rusty Russell <rusty@...tcorp.com.au>
cc:	akpm@...ux-foundation.org, linux-arch@...r.kernel.org,
	linux-kernel@...r.kernel.org, David Miller <davem@...emloft.net>,
	Eric Dumazet <dada1@...mosbay.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Mike Travis <travis@....com>
Subject: Re: [patch 05/41] cpu alloc: Percpu_counter conversion

On Fri, 30 May 2008, Rusty Russell wrote:

> On Friday 30 May 2008 13:56:25 Christoph Lameter wrote:
> > Use cpu_alloc instead of allocpercpu.
> 
> These patches seem like useless churn.
> 
> Plus, the new code is uglier than the old code :(

It drastically reduces the memory size f.e. 4 byte allocations require 
SLAB f.e. to allocate a 32 byte chunk. This reduces memory requirements by
32/4 = 8 times.

Plus the per cpu counters allocated in order are likely placed in the same 
cacheline (whereas the slab allocators avoid placing multiple objects in 
the same cacheline). Reduces cache footprint.

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