Re: [Qemu-devel] [PATCH 16/16] cpus-common: lock-free fast path for cpu_exec_start/end

[Richard Henderson]

On 09/24/2016 04:52 AM, Paolo Bonzini wrote:
> ----- Original Message -----
> > From: "Richard Henderson" <address@hidden>
> > To: "Paolo Bonzini" <address@hidden>, address@hidden
> > Cc: "serge fdrv" <address@hidden>, address@hidden, "alex bennee" <address@hidden>, 
> > "sergey fedorov"
> > <address@hidden>
> > 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);

What I meant is that I don't see that the mutex avoids the need for atomic_set.

> but I can change it anyway to atomic_set.

Thanks,


r~