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

[Peter Xu]

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.

Thanks,

-- 
Peter Xu