netdev - Re: [PATCH 10/11][TG3]: Reduce spurious interrupts.

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Message-ID: <463F656E.5060802@hp.com>
Date:	Mon, 07 May 2007 10:44:14 -0700
From:	Rick Jones <rick.jones2@...com>
To:	Michael Chan <mchan@...adcom.com>
Cc:	David Miller <davem@...emloft.net>, jeff@...zik.org,
	netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH 10/11][TG3]: Reduce spurious interrupts.

Michael Chan wrote:
> On Mon, 2007-05-07 at 09:39 -0700, Rick Jones wrote:
> 
>>On how "topologically big" a system has this resurrection of the PIO read been 
>>tried so far?
>>
> 
> 
> If you're asking how much impact the read will have on performance, the
> answer is that it will depend on whether you frequently get spurious
> interrupts or not without the read.  The read itself has a measurable
> impact on performance, but it will offset the performance hit of
> entering the IRQ handler twice if you get frequent spurious interrupts.
> It also prevents the kernel from shutting down the IRQ in some extreme
> cases.
> 
> If you get spurious interrupts infrequently, the read is unfortunately a
> net loss.

Mostly I was thinking that not all PIO reads are the same "length" and so the 
effect of the PIO read will vary, perhaps considerably, with the platform, 
particularly for a very large NUMA platform.

rick jones
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