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List:       netbsd-port-xen
Subject:    Re: xennet performance collapses with multiple vCPU
From:       Manuel Bouyer <bouyer () antioche ! eu ! org>
Date:       2020-04-13 22:58:54
Message-ID: 20200413225854.GA5670 () antioche ! eu ! org
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On Mon, Apr 13, 2020 at 07:28:32PM +0000, Andrew Doran wrote:
> Ok that's interesting.  I've been all over the IPI code a few times now, and
> tried different things to exclude problems with it, and have found no issue
> there.

I found the problem and commited a fix.

Basically, the scheduler now choose to runs the xennet attach handler
on a different CPU than the boot CPU. The kernel expects the interrupt handler
to be called from this CPU, but Xen still sends the event to CPU 0
(which is the default). The event on CPU 0 is then ignored (the kernel
doens't expect it), and is later processed on the right CPU when a clock
tick causes events processing here.

-- 
Manuel Bouyer <bouyer@antioche.eu.org>
     NetBSD: 26 ans d'experience feront toujours la difference
--
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