linux-kernel - Re: [PATCH] msi: skip calling pci_find_capability from msi_set_mask

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Message-ID: <20080519202654.GE17967@ghostprotocols.net>
Date:	Mon, 19 May 2008 17:26:54 -0300
From:	Arnaldo Carvalho de Melo <acme@...hat.com>
To:	Jesse Barnes <jbarnes@...tuousgeek.org>
Cc:	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>,
	Matthew Wilcox <matthew@....cx>, linux-kernel@...r.kernel.org,
	linux-pci@...r.kernel.org, linux-rt-users@...r.kernel.org
Subject: Re: [PATCH] msi: skip calling pci_find_capability from
	msi_set_mask_bits

Em Mon, May 19, 2008 at 01:11:45PM -0700, Jesse Barnes escreveu:
> On Sunday, May 18, 2008 9:48 pm Hidetoshi Seto wrote:
> > Jesse Barnes wrote:
> > > 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.
> >
> > Humm...
> > I suppose it can be more simple. How about this patch?
> >
> > > everytime handle_edge_irq is called it needs to mask and unmask MSI, and
> > > that leads to a series of very expensive calls to pci_find_capability
> >
> > The position of MSI capability is already cached in the msi_desc when
> > we enter the msi_set_mask_bits().  Use it instead.
> >
> > Signed-off-by: Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>
> 
> Yeah, this looks really nice.  It should also fix Arnaldo's latency problem, 
> and really looks like a bug fix for the MSI code more than anything.
> 
> Arnaldo, can you take a look & test and ack/nack?

I'll do that now

- Arnaldo
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