----- Original Message -----
> From: "Richard Henderson" <r...@twiddle.net>
> To: "Paolo Bonzini" <pbonz...@redhat.com>, qemu-devel@nongnu.org
> Cc: "serge fdrv" <serge.f...@gmail.com>, c...@braap.org, "alex bennee"
> <alex.ben...@linaro.org>, "sergey fedorov"
> <sergey.fedo...@linaro.org>
> Sent: Friday, September 23, 2016 8:23:46 PM
> Subject: Re: [Qemu-devel] [PATCH 16/16] cpus-common: lock-free fast path for
> cpu_exec_start/end
>
> On 09/23/2016 12:31 AM, Paolo Bonzini wrote:
> > + if (atomic_read(&other_cpu->running)) {
> ...
> > + atomic_set(&cpu->running, true);
> ...
> > + cpu->running = false;
> ...
> > + cpu->running = true;
>
> Inconsistent use of atomics. I don't see that the cpu_list_lock protects the
> last two lines in any way.
It does:
qemu_mutex_lock(&qemu_cpu_list_lock);
if (!cpu->has_waiter) {
/* Not counted in pending_cpus, let the exclusive item
* run. Since we have the lock, just set cpu->running to true
* while holding it; no need to check pending_cpus again.
*/
cpu->running = false;
exclusive_idle();
/* Now pending_cpus is zero. */
cpu->running = true;
} else {
/* Counted in pending_cpus, go ahead and release the
* waiter at cpu_exec_end.
*/
}
qemu_mutex_unlock(&qemu_cpu_list_lock);
but I can change it anyway to atomic_set.
Paolo
