Re: [PATCH v2 7/9] cpus: Introduce qemu_mutex_unlock_iothread_prepare()

[David Hildenbrand]

On 27.07.21 18:08, Peter Xu wrote:
> On Tue, Jul 27, 2021 at 02:59:26PM +0200, David Hildenbrand wrote:
> > On 23.07.21 21:34, Peter Xu wrote:
> > > The prepare function before unlocking BQL.  There're only three places that can
> > > release the BQL: unlock(), cond_wait() or cond_timedwait().
> > >
> > > Signed-off-by: Peter Xu <peterx@redhat.com>
> > > ---
> > >    softmmu/cpus.c | 7 +++++++
> > >    1 file changed, 7 insertions(+)
> > >
> > > diff --git a/softmmu/cpus.c b/softmmu/cpus.c
> > > index 9131f77f87..6085f8edbe 100644
> > > --- a/softmmu/cpus.c
> > > +++ b/softmmu/cpus.c
> > > @@ -66,6 +66,10 @@
> > >    static QemuMutex qemu_global_mutex;
> > > +static void qemu_mutex_unlock_iothread_prepare(void)
> > > +{
> > > +}
> > > +
> > >    bool cpu_is_stopped(CPUState *cpu)
> > >    {
> > >        return cpu->stopped || !runstate_is_running();
> > > @@ -523,16 +527,19 @@ void qemu_mutex_unlock_iothread(void)
> > >    {
> > >        g_assert(qemu_mutex_iothread_locked());
> > >        iothread_locked = false;
> > > +    qemu_mutex_unlock_iothread_prepare();
> > >        qemu_mutex_unlock(&qemu_global_mutex);
> > >    }
> > >    void qemu_cond_wait_iothread(QemuCond *cond)
> > >    {
> > > +    qemu_mutex_unlock_iothread_prepare();
> > >        qemu_cond_wait(cond, &qemu_global_mutex);
> > >    }
> > >    void qemu_cond_timedwait_iothread(QemuCond *cond, int ms)
> > >    {
> > > +    qemu_mutex_unlock_iothread_prepare();
> > >        qemu_cond_timedwait(cond, &qemu_global_mutex, ms);
> > >    }
> >
> > I'd squash this patch into the next one.
> >
> > I don't quite like the function name, but don't really have a better
> > suggestion .... maybe qemu_mutex_might_unlock_iothread(), similar to
> > might_sleep() or might_fault() in the kernel. (although here it's pretty
> > clear and not a "might"; could be useful in other context where we might
> > conditionally unlock the BQL at some point in the future, though)
>
> Yes, IMHO "might" describes a capability of doing something, here it's not
> (this one should only be called right before releasing bql, not within any
> context of having some capability).  The other option I thought was "pre" but
> it will be just a short version of "prepare".
>
> Let me know if you have a better suggestion on naming. :) Otherwise I'll keep
> the naming, squash this patch into the next and keep your r-b for that.

Fine with me :)


--
Thanks,

David / dhildenb