linux-kernel - Re: Multiple MSI, take 3

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Date:	Fri, 11 Jul 2008 03:32:42 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	matthew@....cx
Cc:	ebiederm@...ssion.com, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org, grundler@...isc-linux.org,
	mingo@...e.hu, tglx@...utronix.de, jgarzik@...ox.com,
	linux-ide@...r.kernel.org, suresh.b.siddha@...el.com,
	benh@...nel.crashing.org, jbarnes@...tuousgeek.org,
	rdunlap@...otime.net, mtk.manpages@...il.com
Subject: Re: Multiple MSI, take 3

From: Matthew Wilcox <matthew@....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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