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Re: [Qemu-discuss] qemu SMP support

From: Peter Maydell
Subject: Re: [Qemu-discuss] qemu SMP support
Date: Fri, 17 Oct 2014 00:28:50 +0200

On 16 October 2014 21:31, Pranith Kumar <address@hidden> wrote:
> I am trying to gather some instruction execution statistics of a
> multi-threaded program by adding some counters in TCG.
> I've learnt that multi-threaded execution is not supported in user
> mode and in system mode with TCG. Is KVM the only mode which supports
> multi-threaded execution? Or is the support related to SMP mode?

TCG system mode supports running multi-threaded guests fine,
and we support both single CPU and multiple CPU guest configs.
What we don't do is make use of multiple host threads when
we're doing this, so we emulate a 4 core system by running
guest instructions for each core in turn within a single host
thread. This is a performance limitation, not a functional one.
(If you care largely about performance then for TCG you are
best off specifying a single guest CPU config; multiple guest
CPUs will run slower, not faster.)

-- PMM

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