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Re: [Xen-devel] [PATCH v8 10/11] viridian: add implementation of synthetic timers


  • To: Paul Durrant <Paul.Durrant@xxxxxxxxxx>, 'Jan Beulich' <JBeulich@xxxxxxxx>
  • From: Paul Durrant <Paul.Durrant@xxxxxxxxxx>
  • Date: Mon, 18 Mar 2019 15:46:23 +0000
  • Accept-language: en-GB, en-US
  • Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>, Wei Liu <wei.liu2@xxxxxxxxxx>, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>, Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>, "Tim \(Xen.org\)" <tim@xxxxxxx>, George Dunlap <George.Dunlap@xxxxxxxxxx>, Julien Grall <julien.grall@xxxxxxx>, Ian Jackson <Ian.Jackson@xxxxxxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Roger Pau Monne <roger.pau@xxxxxxxxxx>
  • Delivery-date: Mon, 18 Mar 2019 15:49:06 +0000
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  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
  • Thread-index: AQHU3X2WVMvWAzv7yUWT06FGctY0sqYRYLYAgAATJKCAABN4MA==
  • Thread-topic: [Xen-devel] [PATCH v8 10/11] viridian: add implementation of synthetic timers

> -----Original Message-----
[snip]
> > > +    {
> > > +        expiration = vs->count;
> > > +        if ( expiration - now <= 0 )
> > > +        {
> > > +            vs->expiration = expiration;
> > > +            stimer_expire(vs);
> >
> > Aren't you introducing a risk for races by calling the timer function
> > directly from here? start_timer(), after all, gets called from quite a
> > few places.
> >
> 
> In practice I don't think there should be any problematic race, but I'll 
> check again.
> 

I think the 'periodic' name might be confusing things... The Xen timers are all 
single-shot, it's just that start_stimer() is re-called after a successful poll 
if the viridian timer is configured to be periodic. So I don't think there is 
case where the underlying Xen timer could actually be running when we enter 
start_stimer().

  Paul
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