netdev - Re: [PATCH] e1000e: MSI interrupt test failed, using legacy interrupt

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Message-ID: <1335490840.4056.137.camel@deadeye>
Date:	Fri, 27 Apr 2012 02:40:40 +0100
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	<prasanna.panchamukhi@...erbed.com>
CC:	<bruce.w.allan@...el.com>, <jeffrey.t.kirsher@...el.com>,
	<jeffrey.e.pieper@...el.com>, <gospo@...hat.com>,
	<sassmann@...hat.com>, <jesse.brandeburg@...el.com>,
	<e1000-devel@...ts.sourceforge.net>, <netdev@...r.kernel.org>
Subject: Re: [PATCH] e1000e:  MSI interrupt test failed, using legacy
 interrupt

On Thu, 2012-04-26 at 17:05 -0700, prasanna.panchamukhi@...erbed.com
wrote:
> From: Prasanna S. Panchamukhi <ppanchamukhi@...erbed.com>
> 
> Following logs where seen on Systems with multiple NICs & ports,
> while using MSI interrupts as shown below:
[...]
> This patch changes the IRQ tests to use polling loops starting with a
> delay of 1 tick and doubling that if necessary up to a maximum total
> delay of approximately 1 second.
[...]

I don't think you entirely understood my point.  This exponential
back-off was the best I could come up with for a self-test
(ethtool -t) where we have to answer the question 'are interrupts
working' in a reasonable time, and the user can decide for themselves
whether this was a false negative.

If you want a definite answer in order to make an automatic decision
about interrupt modes, there really is no valid time limit.  I think the
proper way to do interrupt mode selection in an in-tree driver is to
rely on no-MSI quirks for chipsets and devices in the PCI core.

Ben.

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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