netdev - Re: [PATCH 1/4]: net: Allow RX queue selection to seed TX queue hashing.

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Message-ID: <20090129044148.GA25131@gondor.apana.org.au>
Date:	Thu, 29 Jan 2009 15:41:48 +1100
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	David Miller <davem@...emloft.net>
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH 1/4]: net: Allow RX queue selection to seed TX queue
	hashing.

On Wed, Jan 28, 2009 at 05:45:22PM -0800, David Miller wrote:
> 
> This is already proven to be false :-)
> 
> Having more TX queues helps a lot.  Robert's testing confirms
> this even when the number of TX queues exceeds the number of
> cores.
> 
> When Robert directly maps RX queues to a single TX queue on NIU, we
> get drops at the qdisc level during his routing tests.  With the TX
> queue iterator which causes all of the TX queues to be utilizied there
> are no drops.

This could just mean that the hardware has underprovisioned each
individual TX queue.  Or is there some fundamental efficiency of
using multiple queues that I have missed?

But yeah if a single TX queue isn't big enough to take care of
the output from a single core then you will need multiple TX
queues.  Although from an system-wide point of view it would
seem to be more optimal to make that TX queue bigger rather than
forcing the software to use multiple queues (which may come with
a bigger overhead) to make up for it.

Of course for us software developers we don't really have a choice :)

Cheers,
-- 
Visit Openswan at http://www.openswan.org/
Email: Herbert Xu ~{PmV>HI~} <herbert@...dor.apana.org.au>
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