netdev - Re: [PATCH v3 net-next] net: introduce dev_set

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Message-ID: <20131104052321.GA23252@gondor.apana.org.au>
Date:	Mon, 4 Nov 2013 13:23:21 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Ben Hutchings <bhutchings@...arflare.com>,
	David Miller <davem@...emloft.net>,
	christoph.paasch@...ouvain.be, netdev@...r.kernel.org,
	hkchu@...gle.com, mwdalton@...gle.com
Subject: Re: [PATCH v3 net-next] net: introduce dev_set_forwarding()

On Sun, Nov 03, 2013 at 09:00:54PM -0800, Eric Dumazet wrote:
> On Mon, 2013-11-04 at 12:29 +0800, Herbert Xu wrote:
>
> > Have you actually measured this? The latency added by GRO is pure
> > processing overhead.  This is tiny when compared to the time NAPI takes
> > to wait.
> 
> Please take a look at 
> 
> 2e71a6f8084e net: gro: selective flush of packets

This is a different problem altogether.  I was worried about the
latency in cases where we're idle and waiting for new data, while
you're worried about the latency in the CPU-bound case.

I think we can definitely improve our behaviour the CPU-bound case.
Right now if we encounter something we can't hold for GRO we
start processing it right away.  Instead we can place it in a
list for later processing together with the GRO packets.

This way GRO packets are not penalised by non-GRO packets.

You can then use the usual NAPI budget to minimise latency and
ensure scheduling fairness.

Cheers,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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