netdev - Re: [patch 1/4] - Potential performance bottleneck for Linxu TCP

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Message-Id: <20061129.181950.31643130.davem@davemloft.net>
Date:	Wed, 29 Nov 2006 18:19:50 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	wenji@...l.gov
Cc:	akpm@...l.org, netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [patch 1/4] - Potential performance bottleneck for Linxu TCP

From: Wenji Wu <wenji@...l.gov>
Date: Wed, 29 Nov 2006 19:56:58 -0600

> >We could also pepper tcp_recvmsg() with some very carefully placed
> >preemption disable/enable calls to deal with this even with
> >CONFIG_PREEMPT enabled.
>
> I also think about this approach. But since the "problem" happens in
> the 2.6 Desktop and Low-latency Desktop (not server), system
> responsiveness is a key feature, simply placing preemption
> disabled/enable call might not work.  If you want to place
> preemption disable/enable calls within tcp_recvmsg, you have to put
> them in the very beginning and end of the call. Disabling preemption
> would degrade system responsiveness.

We can make explicitl preemption checks in the main loop of
tcp_recvmsg(), and release the socket and run the backlog if
need_resched() is TRUE.

This is the simplest and most elegant solution to this problem.

The one suggested in your patch and paper are way overkill, there is
no reason to solve a TCP specific problem inside of the generic
scheduler.
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