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Date: Fri, 13 Aug 2004 12:31:51 +0200
From: Ingo Molnar <mingo@elte.hu>
To: Lee Revell <rlrevell@joe-job.com>
Cc: linux-kernel <linux-kernel@vger.kernel.org>,
       Felipe Alfaro Solana <felipe_alfaro@linuxmail.org>,
       Florian Schmidt <mista.tapas@gmx.net>
Subject: Re: [patch] Latency Tracer, voluntary-preempt-2.6.8-rc4-O6
Message-ID: <20040813103151.GH8135@elte.hu>
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* Lee Revell <rlrevell@joe-job.com> wrote:

> > >   http://redhat.com/~mingo/voluntary-preempt/voluntary-preempt-2.6.8-rc4-O6
> 
> Ugh, this is a bad one:
> 
> preemption latency trace v1.0
> -----------------------------
>  latency: 506 us, entries: 157 (157)
>  process: evolution/3461, uid: 1000
>  nice: 0, policy: 0, rt_priority: 0
> =======>
>  0.000ms (+0.000ms): get_random_bytes (__check_and_rekey)
[...]
>  0.493ms (+0.001ms): local_bh_enable (__check_and_rekey)

indeed this is a new one. Entropy rekeying every 300 seconds. Most of
the overhead comes from the memcpy's - 10 usecs a pop!

this could possibly explain some earlier reports of RTC problems every
couple of minutes - on slower boxes it could easily be more than the 0.5
msec you got. (and with a 8192 Hz RTC the interrupt period is 122
usecs.)

such bhs-off spinlocked sections exclude all softirq traffic - and in
the redirected hardirqs case the hardirqs are excluded too.

	Ingo