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Date: Fri, 20 Aug 2004 12:27:32 +0200
From: Ingo Molnar <mingo@elte.hu>
To: Lee Revell <rlrevell@joe-job.com>
Cc: linux-kernel <linux-kernel@vger.kernel.org>,
       Thomas Charbonnel <thomas@undata.org>,
       Florian Schmidt <mista.tapas@gmx.net>,
       Felipe Alfaro Solana <felipe_alfaro@linuxmail.org>
Subject: Re: [patch] voluntary-preempt-2.6.8.1-P4
Message-ID: <20040820102732.GA14622@elte.hu>
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* Lee Revell <rlrevell@joe-job.com> wrote:

> This is an extreme load situation, so I don't think it will be a
> real-world problem.  I have not seen it under any normal workload.

well, 9 msecs is still not nice. I've been able to trigger larger than
10msec latencies too on a 2 GHz box.

> What about this one:
> 
> http://krustophenia.net/testresults.php?dataset=2.6.8.1-P4#/var/www/2.6.8.1-P4/netif_receive_skb_latency_trace.txt
> 
> This appears during normal use.

hm, tcp_collapse() in net/ipv4/tcp_input.c. Could you try to just return
from that function?  Collapsing skbs of a given socket is not a
necessary functionality (it is only a 'nice' thing to have in OOM
situations) and it indeed can introduce quite high latencies.

	Ingo