[Xen-devel] Re: [PATCH] x86 hvm: fix missing ticks issue in c/s 20218

[Kouya Shimura <kouya@xxxxxxxxxxxxxx>]

Keir, 
Okay, attached is a new patch per your advice. 
I tested it carefully. It works for me.

Christoph,
Could you please test it?

Thanks,
Kouya

Keir Fraser writes:
> On 25/09/2009 10:32, "Kouya Shimura" <kouya@xxxxxxxxxxxxxx> wrote:
> 
> > I've forgotten VCPU switch. Indeed, it's pretty fragile. :-)
> > What about modifying pt_restore_timer() not to advance pt->scheduled?
> > We should rename pending_intr_nr to pending_intr(boolean).
> 
> It's not clear to me that the old logic around pt->pending_intr_nr and
> pt->scheduled really needs to change that drastically. The more we mess with
> this code the more likely we are to break stuff, as it's hard to get good
> coverage of the timer_modes and various ways guest Oses may manage their
> timers.
> 
> I would prefer to see whether moving the update of pt->scheduled out of
> pt_intr_post() and back into the timer_fn() works. That moves us back
> towards what we had before your patches, and therefore I'm more comfortable
> with it.
> 
>  -- Keir
> 

Signed-off-by: Kouya Shimura <kouya@xxxxxxxxxxxxxx>

diff -r 0f8376078dc1 xen/arch/x86/hvm/vpt.c
--- a/xen/arch/x86/hvm/vpt.c    Wed Sep 23 18:19:30 2009 +0100
+++ b/xen/arch/x86/hvm/vpt.c    Fri Sep 25 20:51:52 2009 +0900
@@ -206,6 +206,7 @@ static void pt_timer_fn(void *data)
     pt_lock(pt);
 
     pt->pending_intr_nr++;
+    pt->scheduled += pt->period;
     pt->do_not_freeze = 0;
 
     vcpu_kick(pt->vcpu);
@@ -308,25 +309,24 @@ void pt_intr_post(struct vcpu *v, struct
     }
     else
     {
-        pt->scheduled += pt->period;
-
         if ( mode_is(v->domain, one_missed_tick_pending) ||
              mode_is(v->domain, no_missed_ticks_pending) )
         {
             pt->last_plt_gtime = hvm_get_guest_time(v);
+            pt_process_missed_ticks(pt);
             pt->pending_intr_nr = 0; /* 'collapse' all missed ticks */
+            set_timer(&pt->timer, pt->scheduled);
         }
         else
         {
             pt->last_plt_gtime += pt->period;
             pt->pending_intr_nr--;
-        }
-
-        if ( pt->pending_intr_nr == 0 )
-        {
-            pt_process_missed_ticks(pt);
-            pt->do_not_freeze = 0;
-            set_timer(&pt->timer, pt->scheduled);
+            if ( pt->pending_intr_nr == 0 )
+            {
+                pt_process_missed_ticks(pt);
+                if ( pt->pending_intr_nr == 0 )
+                    set_timer(&pt->timer, pt->scheduled);
+            }
         }
     }
 

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