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Re: [Xen-devel] [PATCH RFC V2 30/45] xen/sched: rework and rename vcpu_force_reschedule()
- To: Jan Beulich <JBeulich@xxxxxxxx>
- From: Juergen Gross <jgross@xxxxxxxx>
- Date: Mon, 6 May 2019 10:51:46 +0200
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- Cc: Tim Deegan <tim@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Wei Liu <wei.liu2@xxxxxxxxxx>, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>, George Dunlap <George.Dunlap@xxxxxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>, Dario Faggioli <dfaggioli@xxxxxxxx>, Julien Grall <julien.grall@xxxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Roger Pau Monne <roger.pau@xxxxxxxxxx>
- Delivery-date: Mon, 06 May 2019 08:51:56 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Openpgp: preference=signencrypt
On 06/05/2019 10:37, Jan Beulich wrote:
>>>> On 06.05.19 at 08:56, <jgross@xxxxxxxx> wrote:
>> --- a/xen/common/schedule.c
>> +++ b/xen/common/schedule.c
>> @@ -808,21 +808,24 @@ static void vcpu_migrate_finish(struct vcpu *v)
>> }
>>
>> /*
>> - * Force a VCPU through a deschedule/reschedule path.
>> - * For example, using this when setting the periodic timer period means that
>> - * most periodic-timer state need only be touched from within the scheduler
>> - * which can thus be done without need for synchronisation.
>> + * Set the periodic timer of a vcpu.
>> */
>> -void vcpu_force_reschedule(struct vcpu *v)
>> +void vcpu_set_periodic_timer(struct vcpu *v, s_time_t value)
>> {
>> - spinlock_t *lock = item_schedule_lock_irq(v->sched_item);
>> + s_time_t now = NOW();
>>
>> - if ( v->sched_item->is_running )
>> - vcpu_migrate_start(v);
>> + if ( v != current )
>> + vcpu_pause(v);
>> + else
>> + stop_timer(&v->periodic_timer);
>>
>> - item_schedule_unlock_irq(lock, v->sched_item);
>> + v->periodic_period = value;
>> + v->periodic_last_event = now;
>
> By the time you come here, NOW() may already be past now + value.
> It's not clear to me whether that'll work correctly; I think it would be
> better to latch NOW() only at this point.
I agree.
Juergen
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