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

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Message-ID: <20090115233220.GD1123@1wt.eu>
Date:	Fri, 16 Jan 2009 00:32:20 +0100
From:	Willy Tarreau <w@....eu>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	David Miller <davem@...emloft.net>, 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 Fri, Jan 16, 2009 at 10:19:35AM +1100, Herbert Xu wrote:
> On Fri, Jan 16, 2009 at 12:03:31AM +0100, Willy Tarreau wrote:
> > 
> > I'm leaving the patch below for comments, maybe someone will spot
> > something ? Don't we need at least one kfree() somewhere to match
> > alloc_pages() ?
> 
> Indeed.
> 
> > >  static inline int spd_fill_page(struct splice_pipe_desc *spd, struct page *page,
> > >  				unsigned int len, unsigned int offset,
> > > -				struct sk_buff *skb)
> > > +				struct sk_buff *skb, int linear)
> > >  {
> > >  	if (unlikely(spd->nr_pages == PIPE_BUFFERS))
> > >  		return 1;
> > >  
> > > +	if (linear) {
> > > +		page = linear_to_page(page, len, offset);
> > > +		if (!page)
> > > +			return 1;
> > > +	}
> > > +
> > >  	spd->pages[spd->nr_pages] = page;
> > >  	spd->partial[spd->nr_pages].len = len;
> > >  	spd->partial[spd->nr_pages].offset = offset;
> > > -	spd->partial[spd->nr_pages].private = (unsigned long) skb_get(skb);
> > >  	spd->nr_pages++;
> > > +	get_page(page);
> 
> This get_page needs to be moved into an else clause of the previous
> if block.

Good catch Herbert, it's working fine now. The performance I get
(30.6 MB/s) is between the original splice version (24.1) and the
recently optimized one (35.7). That's not that bad considering
we're copying the data.

Cheers,
Willy

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