netdev - Re: [PATCH] rps: make distributing packets fairly among all the online CPUs default

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Date:	Tue, 23 Mar 2010 12:38:26 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Changli Gao <xiaosuo@...il.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Tom Herbert <therbert@...gle.com>, netdev@...r.kernel.org,
	Ben Hutchings <bhutchings@...arflare.com>
Subject: Re: [PATCH] rps: make distributing packets fairly among all the 
 online CPUs default

Le mardi 23 mars 2010 à 18:03 +0800, Changli Gao a écrit :

> 
> Ben Hutchings raised this question, but nobody replied with any message.
> 
> I do think distributing packets fairly among all the online CPUs will
> helps most of users. I remember the smp_affinity of IRQ is the
> online_cpu_mask be default.
> 

I know _many_ applications that perform better when all network IRQS are
directed to one CPU only. Single threaded UDP server for example, with
fast answer, or routers, or ...

Many sysadmins tuned their machine to meet this requirement. Installing
2.6.35, if RPS enabled by default will make them unhappy, especially if
CONFIG_SYSFS is not set, since they wont be able to change RPS settings.

If RPS was good for all workloads, activating it would make sense, but
this is not the case.

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