netdev - Re: why all packets have same queue no when rps enabled?

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Date:	Tue, 22 Feb 2011 12:45:56 +0000
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Jon Zhou <Jon.Zhou@...u.com>
Cc:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: why all packets have same queue no when rps enabled?

On Mon, 2011-02-21 at 20:07 -0800, Jon Zhou wrote:
> Hi
> 
> I expect each incoming packet will have a different queue no. when I
> enabled RPS on kernel 2.6.36.4
[...]
> Looks almost all packets fall at same queue?
> Will RPS allocate queue no for each packet? and what hash algorithm
> rps used? (is it Toeplitz hash algorithm?)

The queue number identifies a hardware queue.  RPS therefore does not
update this number when queueing packets for processing on other CPUs.

If the hardware/driver provides a receive hash (probably Toeplitz) then
this is used for RPS.  Otherwise a much cheaper hash is used.

Ben.

-- 
Ben Hutchings, Senior Software Engineer, Solarflare Communications
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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