linux-kernel - Re: [PATCH][PCI]: Introduce pci_find_capability

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Message-ID: <20080516183356.GA7307@ghostprotocols.net>
Date:	Fri, 16 May 2008 15:33:56 -0300
From:	Arnaldo Carvalho de Melo <acme@...hat.com>
To:	Jesse Barnes <jbarnes@...tuousgeek.org>
Cc:	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Matthew Wilcox <matthew@....cx>, linux-kernel@...r.kernel.org,
	linux-pci@...r.kernel.org, linux-rt-users@...r.kernel.org
Subject: Re: [PATCH][PCI]: Introduce pci_find_capability_cached and make
	MSI use it

Em Fri, May 16, 2008 at 10:44:34AM -0700, Jesse Barnes escreveu:
> On Thursday, May 15, 2008 10:10 am Arnaldo Carvalho de Melo wrote:
> > Em Thu, May 15, 2008 at 11:04:07AM -0600, Matthew Wilcox escreveu:
> > > On Thu, May 15, 2008 at 01:04:26PM -0300, Arnaldo Carvalho de Melo wrote:
> > > > 	So I implemented pci_find_capability_cached and made MSI use it
> > > > for good measure, please consider applying.
> > >
> > > As I told you on IRC, this is just the MSI code being complete crap.
> > > It should be caching the offset itself.  We shouldn't have this extra
> > > array in the struct pci_dev just because MSI is broken.
> >
> > Well, we can certainly do that, its just that I did this first and
> > thought that perhaps there could be some other users, but I see that 44
> > extra bytes per pci_dev can be a pain if the only one to reap benefits
> > is MSI, can't you think of any other users? I couldn't detect any so far
> > in my admitedly limited testing.
> 
> There are a few other common cap checks, but I don't think they compare to MSI 
> in terms of latency sensitivity (though I didn't audit all the CAP_ID_EXP 
> checks, there are quite a few of those).
> 
> Since we know MSI is a problem, let's just go with fixing that for now.  If we 
> find that other caps are also causing problems we can revisit caching all of 
> them; the patch is simple enough.

Do you want me to submit another patch or can you cook up one?

- Arnaldo
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