Re: [Xen-devel] IRQ SMP affinity problems in domU with vcpus > 4 on HP ProLiant G6 with dual Xeon 5540 (Nehalem)

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

On 22/10/2009 09:41, "Zhang, Xiantao" <xiantao.zhang@xxxxxxxxx> wrote:

>> Hmm, then I don't understand which case your patch was a fix for: I
>> understood that it addresses an issue when the affinity of an
>> interrupt gets changed (requiring a re-write of the address/data
>> pair). If the hypervisor can deal with it without masking, then why
>> did you add it?
> 
> Hmm, sorry, seems I misunderstood your question. If the msi doesn't support
> mask bit(clearing MSI enable bit doesn't help in this case), the issue may
> still exist. Just checked Linux side, seems it doesn't perform mask operation
> when program MSI, but don't know why Linux hasn't such issues.  Actaully, we
> do see inconsisten interrupt message from the device without this patch, and
> after applying the patch, the issue is gone.  May need further investigation
> why Linux doesn't need the mask operation.

Linux is quite careful about when it will reprogram vector/affinity info
isn't it? Doesn't it mark such an update pending and only flush it through
during next interrupt delivery, or something like that? Do we need some of
the upstream Linux patches for this?

 -- Keir



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