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Date: Tue, 20 Mar 2007 08:39:30 +0100
From: Eric Dumazet <dada1@cosmosbay.com>
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To: Pekka Enberg <penberg@cs.helsinki.fi>
CC: Andrew Morton <akpm@linux-foundation.org>, mpm@selenic.com,
       Christoph Lameter <clameter@sgi.com>, "ast@domdv.de" <ast@domdv.de>,
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Subject: Re: [PATCH] slab: deal with NULL pointers passed to kmem_cache_free
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Pekka Enberg a écrit :
> On 3/19/07, Andrew Morton <akpm@linux-foundation.org> wrote:
>> This is a super-hot path.
> 
> Super-hot exactly where?

Don't be silly Pekka ... We have plenty oprofiles results if you dont trust 
Andrew.

CPU: AMD64 processors, speed 1992.52 MHz (estimated)
Counted CPU_CLK_UNHALTED events (Cycles outside of halt state) with a unit 
mask of 0x00 (No unit mask) count 100000
samples  %        symbol name
1861563   4.7882  tg3_start_xmit_dma_bug
1375727   3.5386  memcpy_c
1166438   3.0002  tcp_v4_rcv
1157334   2.9768  kmem_cache_free

In this workload (real server), you can see kmem_cache_free() is number four.

Adding one test and conditional branch in this super-hot function just to 
correct a bug in a SCSI driver (or whatever) is not *SANE*.


Numbers talk.