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

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Message-ID: <20061130102205.GA20654@2ka.mipt.ru>
Date:	Thu, 30 Nov 2006 13:22:06 +0300
From:	Evgeniy Polyakov <johnpol@....mipt.ru>
To:	Nick Piggin <nickpiggin@...oo.com.au>
Cc:	Ingo Molnar <mingo@...e.hu>, David Miller <davem@...emloft.net>,
	wenji@...l.gov, akpm@...l.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 1/4] - Potential performance bottleneck for Linxu TCP

On Thu, Nov 30, 2006 at 09:07:42PM +1100, Nick Piggin (nickpiggin@...oo.com.au) wrote:
> >Doesn't the provided solution is just a in-kernel variant of the
> >SCHED_FIFO set from userspace? Why kernel should be able to mark some
> >users as having higher priority?
> >What if workload of the system is targeted to not the maximum TCP
> >performance, but maximum other-task performance, which will be broken
> >with provided patch.
> 
> David's line of thinking for a solution sounds better to me. This patch
> does not prevent the process from being preempted (for potentially a long
> time), by any means.

It steals timeslices from other processes to complete tcp_recvmsg()
task, and only when it does it for too long, it will be preempted.
Processing backlog queue on behalf of need_resched() will break fairness
too - processing itself can take a lot of time, so process can be
scheduled away in that part too.

> -- 
> SUSE Labs, Novell Inc.
> Send instant messages to your online friends http://au.messenger.yahoo.com 

-- 
	Evgeniy Polyakov
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