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

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Date:	Fri, 16 Jan 2009 00:42:55 +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

On Thu, Jan 15, 2009 at 03:34:49PM -0800, David Miller wrote:
> From: Herbert Xu <herbert@...dor.apana.org.au>
> Date: Fri, 16 Jan 2009 10:32:05 +1100
> 
> > On Thu, Jan 15, 2009 at 03:26:08PM -0800, David Miller wrote:
> > > +static inline struct page *linear_to_page(struct page *page, unsigned int len,
> > > +					  unsigned int offset)
> > > +{
> > > +	struct page *p = alloc_pages(GFP_KERNEL, 0);
> > > +
> > > +	if (!p)
> > > +		return NULL;
> > > +	memcpy(page_address(p) + offset, page_address(page) + offset, len);
> > 
> > This won't work very well if skb->head is longer than a page.
> > 
> > We'll need to divide it up into individual pages.
> 
> Oh yes the same bug I pointed out the other day.
> 
> But Willy can test this patch as-is,

Hey, nice work Dave. +3% performance from your previous patch
(31.6 MB/s). It's going fine and stable here.

> since he is not using jumbo frames in linear SKBs.

If you're interested, this week-end I can do some tests on my
myri10ge NICs which support LRO. I frequently observe 23 kB
packets there, and they also support jumbo frames. Those should
cover the case above.

I'm afraid that's all for me for this evening, I have to get some
sleep before going to work. If you want to cook up more patches,
I'll be able to do a bit of testing in 5 hours now.

Cheers!
Willy

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