Re: [Xen-devel] [PATCH v10 11/20] x86/VPMU: Interface for setting PMU mode and flags

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> Sent: Friday, September 19, 2014 6:28 AM
> 
> >>> On 19.09.14 at 14:42, <boris.ostrovsky@xxxxxxxxxx> wrote:
> > On 09/19/2014 02:51 AM, Jan Beulich wrote:
> >>>>> On 18.09.14 at 23:50, <boris.ostrovsky@xxxxxxxxxx> wrote:
> >>> On 09/18/2014 12:11 AM, Tian, Kevin wrote:
> >>>>> From: Boris Ostrovsky [mailto:boris.ostrovsky@xxxxxxxxxx]
> >>>>> +{
> >>>>> +    unsigned i, j, allbutself_num, tasknum, mycpu;
> >>>>> +    static s_time_t start;
> >>>>> +    static struct tasklet **sync_task;
> >>>>> +    struct vcpu *curr_vcpu = current;
> >>>>> +    static struct vcpu *sync_vcpu;
> >>>>> +    int ret = 0;
> >>>>> +
> >>>>> +    tasknum = allbutself_num = num_online_cpus() - 1;
> >>>>> +
> >>>>> +    if ( sync_task ) /* if set, we are in hypercall continuation */
> >>>>> +    {
> >>>>> +        if ( (sync_vcpu != NULL) && (sync_vcpu != curr_vcpu) )
> >>>>> +            /* We are not the original caller */
> >>>>> +            return -EAGAIN;
> >>>> I assume hypercall continuation will happen on original vcpu context.
> Under
> >>>> which situation the hypercall will be continued on a different vcpu? If
> yes,
> >>>> would it be an unbounded situation where you may wait unexpected time
> >>>> to have sync_vcpu==curr_vcpu?
> >>> The continuation call is gone in v11. If we are stuck waiting for more
> >>> than 5 seconds we'll simply return -EAGAIN and have the caller retry.
> >> That reads wrong, but I'd of course have to see whether the just
> >> wording above is incorrectly reflecting the code changes you did.
> >
> > The only thing that I can think of that I didn't mention is
> > hypercall_preempt_check() to bail out earlier than 5 seconds. Is that
> > what you are missing in my reply? Otherwise  I don't know what else is
> > wrong.
> 
> Yes, that indeed was the missing piece.
> 

Is v11 out or not? I didn't find it in my inbox.

Thanks
Kevin

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