Subject: Re: [PATCH V3] xen-evtchn: Bind dyn evtchn:qemu-dm interrupt to next
 online VCPU
To: Anoob Soman <anoob.soman@citrix.com>, xen-devel@lists.xenproject.org,
        linux-kernel@vger.kernel.org
References: <1496836016-7053-1-git-send-email-anoob.soman@citrix.com>
Cc: jgross@suse.com
From: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Message-ID: <7b3c806e-61b4-b840-79ea-8beb27f0ba3f@oracle.com>
Date: Wed, 7 Jun 2017 10:34:02 -0400
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On 06/07/2017 07:46 AM, Anoob Soman wrote:
> A HVM domian booting generates around 200K (evtchn:qemu-dm xen-dyn)
> interrupts,in a short period of time. All these evtchn:qemu-dm are bound
> to VCPU 0, until irqbalance sees these IRQ and moves it to a different VCPU.
> In one configuration, irqbalance runs every 10 seconds, which means
> irqbalance doesn't get to see these burst of interrupts and doesn't
> re-balance interrupts most of the time, making all evtchn:qemu-dm to be
> processed by VCPU0. This cause VCPU0 to spend most of time processing
> hardirq and very little time on softirq. Moreover, if dom0 kernel PREEMPTION
> is disabled, VCPU0 never runs watchdog (process context), triggering a
> softlockup detection code to panic.
>
> Binding evtchn:qemu-dm to next online VCPU, will spread hardirq
> processing evenly across different CPU. Later, irqbalance will try to balance
> evtchn:qemu-dm, if required.
>
> Signed-off-by: Anoob Soman <anoob.soman@citrix.com>

Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>