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[Xen-devel] Re: Can we remove the logic of preventing MSI irq storms

To: Haitao Shan <maillists.shan@xxxxxxxxx>
Subject: [Xen-devel] Re: Can we remove the logic of preventing MSI irq storms
From: Keir Fraser <keir.xen@xxxxxxxxx>
Date: Thu, 14 Jul 2011 08:06:59 +0100
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Thread-topic: Can we remove the logic of preventing MSI irq storms
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On 14/07/2011 07:43, "Haitao Shan" <maillists.shan@xxxxxxxxx> wrote:

> Hi, Keir,
> As you may remember (see c/s 17960), Xen implemented the logic of
> preventing MSI irq storms. The reason of the IRQ storm at that time is
> still unknown. But the logic is definitely needed at that time since
> that NIC is the only device at my hand to test MSI.
> The idea is simple: mask the second MSI interrupt when the first one
> is still in processing. For HVM guests, we hooked at guest EOI write
> to determime whether the first MSI is serviced already.
> However, recently we find the logic has negative impact on 10G NIC
> performance (assigned to guest). The logic lowers the interrupt
> frequency that Xen can handle. It is a problem when the device is
> generating too many interrupts as seen in this 10G NIC.
> And now there is IRQ rate limit logic in Xenm which can also help to
> prevent IRQ storms.
> Given all the above, do you think it is time to remove the logic of
> preventing MSI IRQ storm?

I'd be happy to see it go.

 -- Keir

> Shan Haitao

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