[Xen-devel] [PATCH 2/4] CPUIDLE: Avoid remnant LAPIC timer intr while force hpetbroadcast

["Wei, Gang" <gang.wei@xxxxxxxxx>]

CPUIDLE: Avoid remnant LAPIC timer intr while force hpetbroadcast

LAPIC will stop during C3, and resume to work after exit from C3. Considering 
below case:
The LAPIC timer was programmed to expire after 1000us, but CPU enter C3 after 
100us and exit C3 at 9xxus.

   0us: reprogram_timer(1000us)
 100us: entry C3, LAPIC timer stop
 9xxus: exit C3 due to unexpected event, LAPIC timer continue running
10xxus: reprogram_timer(1000us), fail due to the past expiring time.
......: no timer softirq raised, no change to LAPIC timer.
......: if entry C3 again, HPET will be forced reprogramed to now+small_slop.
......: if entry C2, no change to LAPIC.
18xxus: LAPIC timer expires unexpectedly if no C3 entries after 10xxus.

>From above sequences, we can find this case will either introduce extra HPET 
>intrs or put off the softtimer expiring.
This patch simply stops the LAPIC timer first (avoid immediate unnecessary 
expiring) and raise a softirq (continue the softtimer handling process, which 
will correct the LAPIC timer) when reprogram LAPIC timer fails.

Signed-off-by: Wei Gang <gang.wei@xxxxxxxxx>

Attachment: cancel_useless_timer_intr_0909.patch
Description: cancel_useless_timer_intr_0909.patch

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel