lkml.org 
[lkml]   [2007]   [Mar]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: [PATCH 2.6.21-rc5] MSI: read-flush MSI-X table
Date
Greg KH <greg@kroah.com> writes:

> On Mon, Mar 26, 2007 at 04:18:22PM -0700, Mitch Williams wrote:
>> This patch fixes a kernel bug which is triggered when using the
>> irqbalance daemon with MSI-X hardware.
>>
>> Because both MSI-X interrupt messages and MSI-X table writes are posted,
>> it's possible for them to cross while in-flight. This results in
>> interrupts being received long after the kernel thinks they're disabled,
>> and in interrupts being sent to stale vectors after rebalancing.
>>
>> This patch performs a read flush after writes to the MSI-X table for
>> enable/disable and rebalancing operations. Because this is an expensive
>> operation, we do not perform the read flush after mask/unmask
>> operations. Hardware which supports MSI-X typically also supports some
>> sort of interrupt moderation, so a read-flush is not necessary for
>> mask/unmask operations.
>>
>> This patch has been validated with (unreleased) network hardware which
>> uses MSI-X.
>
> How well does this play with the MSI core changes that Michael Ellerman
> has proposed on the linux-pci mailing list?

I guess I should add that I'm not certain that the code is exactly correct
there are weird differences between enable/disable and mask. Where generally
the mask/unmask methods do the work and enable/disable do some weird software
thing. Having them different and enable/disable not doing some software
thing concerns me a little. I think mask/unmask may been overoptimized
in this case.

So I expect someone will wind up refactor this code at some point.

However the code is clearly better than what we have now, and it can't
affect anything else.

Eric
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2007-03-27 15:27    [from the cache]
©2003-2011 Jasper Spaans