From: Stefan Hajnoczi <stefanha@redhat.com>
To: "Alex Bennée" <alex.bennee@linaro.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
qemu-devel@nongnu.org,
Peter Crosthwaite <crosthwaite.peter@gmail.com>,
Richard Henderson <rth@twiddle.net>
Subject: Re: [Qemu-devel] [PATCH] cpus: make qemu_mutex_iothread_locked() understand co-routines
Date: Wed, 2 Nov 2016 14:06:53 +0000 [thread overview]
Message-ID: <20161102140653.GH4693@stefanha-x1.localdomain> (raw)
In-Reply-To: <871syvxjan.fsf@linaro.org>
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On Tue, Nov 01, 2016 at 04:21:36PM +0000, Alex Bennée wrote:
>
> Paolo Bonzini <pbonzini@redhat.com> writes:
>
> > On 21/10/2016 13:54, Alex Bennée wrote:
> >> There is a slight wart when checking for the state of the BQL when using
> >> GThread base co-routines (which we keep for ThreadSanitizer runs). While
> >> the main-loop holds the BQL it is suspended until the co-routine
> >> completes however the co-routines run in a separate thread so checking
> >> the TLS variable could be wrong.
> >>
> >> We fix this by expanding the check to include qemu_in_coroutine() for
> >> GThread based builds. As it is not used for production builds I'm not
> >> overly worried about any performance impact which should be negligible
> >> anyway.
> >>
> >> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
> >> Cc: Stefan Hajnoczi <stefanha@redhat.com>
> >
> > This is wrong unfortunately. It is possible to run coroutines outside
> > the BQL (e.g. with -device virtio-blk,iothread=foo).
> >
> > Do you know exactly why TSAN has no love for coroutines?
>
> The current production stuff is due to missing support for new stacks
> with setcontext. However I have built the latest tsan support library
> and that seems happy without the gthread co-routines.
>
> Currently I'm dealing with glib's racy gthread support however.
I think Paolo suggested we drop the GThread backend on IRC. I agree
that we should do that since GThread co-routines break code that uses
thread-local variables and have never truly worked.
Stefan
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next prev parent reply other threads:[~2016-11-02 14:07 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-10-21 11:54 [Qemu-devel] [PATCH] cpus: make qemu_mutex_iothread_locked() understand co-routines Alex Bennée
2016-11-01 15:04 ` Paolo Bonzini
2016-11-01 16:21 ` Alex Bennée
2016-11-02 14:06 ` Stefan Hajnoczi [this message]
2016-11-02 14:55 ` Alex Bennée
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