Re: [Qemu-devel] Linux kernel polling for QEMU

["Alex Bennée" <alex.bennee@linaro.org>]

Paolo Bonzini <pbonzini@redhat.com> writes:

> 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.

The patch itself is:

    tcg: add kick timer for single-threaded vCPU emulation

It's not really part of MTTCG as it can be applied without reference to
the MTTCG work. However it is a pre-requisite to the iothread mutex
rework that MTTCG requires which would otherwise break the single
threaded case which currently relies on the side-effect to trigger
scheduling.

>
> Paolo


--
Alex Bennée