linux-kernel - Re: [PATCH] xen/netback: calculate correctly the SKB slots.

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Message-ID: <20120523131242.GA15406@phenom.dumpdata.com>
Date:	Wed, 23 May 2012 09:12:42 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Simon Graham <simon.graham@...rix.com>
Cc:	Ian Campbell <Ian.Campbell@...rix.com>,
	Ben Hutchings <bhutchings@...arflare.com>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Adnan Misherfi <adnan.misherfi@...cle.com>
Subject: Re: [PATCH] xen/netback: calculate correctly the SKB slots.

On Tue, May 22, 2012 at 03:01:55PM -0400, Simon Graham wrote:
> > >
> > > > >  	int i, copy_off;
> > > > >
> > > > >  	count = DIV_ROUND_UP(
> > > > > -			offset_in_page(skb->data)+skb_headlen(skb),
> > PAGE_SIZE);
> > > > > +			offset_in_page(skb->data + skb_headlen(skb)),
> > PAGE_SIZE);
> > > >
> > > > The new version would be equivalent to:
> > > > 	count = offset_in_page(skb->data + skb_headlen(skb)) != 0;
> > > > which is not right, as netbk_gop_skb() will use one slot per page.
> > >
> > > Just outside the context of this patch we separately count the frag
> > > pages.
> > >
> > > However I think you are right if skb->data covers > 1 page, since the
> > > new version can only ever return 0 or 1. I expect this patch papers
> > over
> > > the underlying issue by not stopping often enough, rather than
> > actually
> > > fixing the underlying issue.
> > 
> > Ah, any thoughts? Have you guys seen this behavior as well?
> 
> We ran into this same problem and the fix we've been running with for a while now (been meaning to submit it!) is:

Where is the patchqueue of the patches? Is it only on the src.rpm or
is it in some nice mercurial tree? Asking b/c if we run into other trouble
it would be also time-saving for us (and I presume other companies
too) to check that. Thanks!
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