Date: Fri, 11 Jul 2008 03:32:42 -0700 (PDT)
Message-Id: <20080711.033242.58168774.davem@davemloft.net>
To: matthew@wil.cx
Cc: ebiederm@xmission.com, linux-pci@vger.kernel.org,
       linux-kernel@vger.kernel.org, grundler@parisc-linux.org, mingo@elte.hu,
       tglx@linutronix.de, jgarzik@pobox.com, linux-ide@vger.kernel.org,
       suresh.b.siddha@intel.com, benh@kernel.crashing.org,
       jbarnes@virtuousgeek.org, rdunlap@xenotime.net, mtk.manpages@gmail.com
Subject: Re: Multiple MSI, take 3
From: David Miller <davem@davemloft.net>
In-Reply-To: <20080711102326.GR14894@parisc-linux.org>
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	<20080711102326.GR14894@parisc-linux.org>
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From: Matthew Wilcox <matthew@wil.cx>
Date: Fri, 11 Jul 2008 04:23:26 -0600

> On Fri, Jul 11, 2008 at 03:06:33AM -0700, Eric W. Biederman wrote:
> > So unless the performance of the AHCI is better by a huge amount I don't
> > see the point, and even then I am extremely sceptical.
> 
> I don't have performance numbers yet, but surely you can see that
> avoiding a register read in the interrupt path is a large win?

Such overhead is going to be amortized.

AHCI is not like networking where we have lots of very small
transactions to deal with, and therefore the per-IRQ overhead can
begin to dominate.

Therefore, like Eric, I think workng on multiple MSI is a very dubious
usage of one's time.  But, it's your time, so use it how you wish :)
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