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From: Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <3677a5ef-a01c-b867-178b-8287017176d3@redhat.com>
Date: Wed, 30 Nov 2016 15:18:32 +0100
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Subject: Re: [Qemu-devel] Linux kernel polling for QEMU
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To: Peter Maydell <peter.maydell@linaro.org>, Andrew Jones <drjones@redhat.com>
Cc: Fam Zheng <famz@redhat.com>, Eliezer Tamir <eliezer.tamir@linux.intel.com>, "Michael S. Tsirkin" <mst@redhat.com>, QEMU Developers <qemu-devel@nongnu.org>, Jens Axboe <axboe@fb.com>, Christian Borntraeger <borntraeger@de.ibm.com>, Stefan Hajnoczi <stefanha@redhat.com>, Davide Libenzi <davidel@xmailserver.org>, Christoph Hellwig <hch@lst.de>, =?UTF-8?Q?Alex_Benn=c3=a9e?= <alex.bennee@linaro.org>



On 30/11/2016 10:46, Peter Maydell wrote:
>> > The problem is indeed with the scheduling. The way it currently works
>> > is to depend on the iothread to kick a reschedule once in a while, or
>> > a cpu to issue an instruction that does so (wfe/wfi). However if
>> > there's no io and a cpu never issues a scheduling instruction, then it
>> > won't happen. We either need a sched tick or to never have an infinite
>> > iothread ppoll timeout (basically using the ppoll timeout as a tick).
> Ah yes, that one. I thought Alex had a patch which added
> a timer to ensure that we don't allow a single guest
> TCG vCPU to hog the execution thread, but maybe I'm
> misremembering.

Yes, it's part of MTTCG.

Paolo