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Re: [patch 05/10] fs: remove extra lookup in __lookup_hash
- From: "Frank Ch. Eigler" <fche at redhat dot com>
- To: andi at firstfloor dot org
- Cc: systemtap at sources dot redhat dot com
- Date: Wed, 18 Aug 2010 13:57:32 -0400
- Subject: Re: [patch 05/10] fs: remove extra lookup in __lookup_hash
Hi, Andi -
On linux-fsdevel, you wrote:
> As a quick experiment I set a systemtap probe for this on my workstation
>
> global first, second
> probe kernel.function("*@fs/namei.c:1143") { first++ }
> probe kernel.function("*@fs/namei.c:1149") { second++ }
> probe end { printf("first %d, second %d\n", first, second) }
>
> and did a quick kernel build, resulting in:
>
> first 22753, second 22753
This probably isn't doing what you thought. You probably should have
used kernel.statement() instead of kernel.function(). Plus if you
use stap -t, you wouldn't need those two explicit counters; you'd
get hit counts/timings for each probe point at script end.
- FChE