netdev - Re: [PATCH net-next-2.6] net: speedup udp receive path

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Date:	Sat, 01 May 2010 15:22:05 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	hadi@...erus.ca
Cc:	Changli Gao <xiaosuo@...il.com>,
	David Miller <davem@...emloft.net>, therbert@...gle.com,
	shemminger@...tta.com, netdev@...r.kernel.org,
	Eilon Greenstein <eilong@...adcom.com>,
	Brian Bloniarz <bmb@...enacr.com>
Subject: Re: [PATCH net-next-2.6] net: speedup udp receive path

Le samedi 01 mai 2010 à 07:56 -0400, jamal a écrit :

> 
> [1]i.e with this program rps was getting worse (it was much better
> before say net-next of apr14) and that non-rps has been getting better
> numbers since. The regression is real - but it is likely in another
> subsystem.
> 

You must understand that the whole 'bench' is mostly governed by
scheduler artifacts. The regression you mention is probably a side
effect.

By slowing down one part, its possible to zap all calls to scheduler and
go maybe 300% faster (Because consumer threads can avoid 3/4 of the time
to schedule)

Reciprocally, optimizing one part of the network stack might make
threads hitting an empty queue, and need to call more often the
scheduler.

This is why some higly specialized programs never block/schedule and
perform busy loops instead.



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