netdev - Re: [PATCH] tcp: splice as many packets as possible at once

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Date:	Mon, 19 Jan 2009 01:42:06 +0100
From:	Willy Tarreau <w@....eu>
To:	David Miller <davem@...emloft.net>
Cc:	herbert@...dor.apana.org.au, jarkao2@...il.com, zbr@...emap.net,
	dada1@...mosbay.com, ben@...s.com, mingo@...e.hu,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	jens.axboe@...cle.com
Subject: Re: [PATCH] tcp: splice as many packets as possible at once

Hi guys,

On Thu, Jan 15, 2009 at 03:54:34PM -0800, David Miller wrote:
> From: Willy Tarreau <w@....eu>
> Date: Fri, 16 Jan 2009 00:44:08 +0100
> 
> > And BTW feel free to add my Tested-by if you want in case you merge
> > this fix.
> 
> Done, thanks Willy.

Just for the record, I've now re-integrated those changes in a test kernel
that I booted on my 10gig machines. I have updated my user-space code in
haproxy to run a new series of tests. Eventhough there is a memcpy(), the
results are EXCELLENT (on a C2D 2.66 GHz using Myricom's Myri10GE NICs) :

  - 4.8 Gbps at 100% CPU using MTU=1500 without LRO
    (3.2 Gbps at 100% CPU without splice)

  - 9.2 Gbps at 50% CPU using MTU=1500 with LRO

  - 10 Gbps at 20% CPU using MTU=9000 without LRO (7 Gbps at 100% CPU without
    splice)

  - 10 Gbps at 15% CPU using MTU=9000 with LRO

These last ones are really impressive. While I had already observed such
performance on the Myri10GE with Tux, it's the first time I can reach that
level with so little CPU usage in haproxy !

So I think that the memcpy() workaround might be a non-issue for some time.
I agree it's not beautiful but it works pretty well for now.

The 3 patches I used on top of 2.6.27.10 were the fix to return 0 intead of
-EAGAIN on end of read, the one to process multiple skbs at once, and Dave's
last patch based on Jarek's workaround for the corruption issue.

Cheers,
Willy

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