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List:       linux-kernel
Subject:    Re: [patch] voluntary-preempt-2.6.8.1-P5
From:       Ingo Molnar <mingo () elte ! hu>
Date:       2004-08-21 10:46:26
Message-ID: 20040821104626.GA29078 () elte ! hu
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* Lee Revell <rlrevell@joe-job.com> wrote:

> 
> This one is interesting.  What is going on here?
> 
> preemption latency trace v1.0.1
> -------------------------------
>  latency: 146 us, entries: 45 (45)
>     -----------------
>     | task: pdflush/33, uid:0 nice:0 policy:0 rt_prio:0
>     -----------------
>  => started at: find_get_pages_tag+0x19/0x90
>  => ended at:   find_get_pages_tag+0x61/0x90
> =======>
> 00000001 0.000ms (+0.000ms): find_get_pages_tag (pagevec_lookup_tag)
> 00000001 0.000ms (+0.000ms): radix_tree_gang_lookup_tag (find_get_pages_tag)
> 00000001 0.001ms (+0.000ms): __lookup_tag (radix_tree_gang_lookup_tag)
> 00000001 0.007ms (+0.005ms): __lookup_tag (radix_tree_gang_lookup_tag)
> 
> [ 20-30 more of these ]

this is the pagevec code, triggering the radix tree multi-entry-lookup
code. Could you try to reduce PAGEVEC_SIZE from 16 to 8 (or 4) in
include/linux/pagevec.h - does this reduce these particular latencies?

	Ingo
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