Re: [Qemu-devel] [PATCH] qemu-clock: add an alarm timer based on timerfd

[Paolo Bonzini <pbonzini@redhat.com>]

Il 18/09/2012 22:37, Anthony Liguori ha scritto:
> Unfortunately, there's a lot of Windows code in qemu-timer.c and main-loop.c
> right now otherwise the refactoring would be trivial.  I'll leave that for
> another day.
> 
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Jan Kiszka <jan.kiszka@siemens.com>
> Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
> ---
> Please note, this is lightly tested.  Since this is such a fundamental change,
> I'd like to do some performance analysis before committing but wanted to share
> early.

Looks good.  I think Peter Portante tested something similar, and found no big
difference between the two.  But it's a good thing and, in my opinion, for
non-timerfd OSes we should simply adjust the select() timeout and not bother
with signals.

I'm not sure if the same can be done for Windows, but I think it's possible as long
as you keep the timeBeginPeriod/timeEndPeriod calls.  As a start, Stefan, can you
check if the win32 timer works for you with the calls added?  Like this:

diff --git a/qemu-timer.c b/qemu-timer.c
index c7a1551..721c769 100644
--- a/qemu-timer.c
+++ b/qemu-timer.c
@@ -673,6 +673,10 @@ static int win32_start_timer(struct qemu_alarm_timer *t)
     HANDLE hTimer;
     BOOLEAN success;
 
+    timeGetDevCaps(&mm_tc, sizeof(mm_tc));
+
+    timeBeginPeriod(mm_tc.wPeriodMin);
+
     /* If you call ChangeTimerQueueTimer on a one-shot timer (its period
        is zero) that has already expired, the timer is not updated.  Since
        creating a new timer is relatively expensive, set a bogus one-hour
@@ -688,6 +692,7 @@ static int win32_start_timer(struct qemu_alarm_timer *t)
     if (!success) {
         fprintf(stderr, "Failed to initialize win32 alarm timer: %ld\n",
                 GetLastError());
+        timeEndPeriod(mm_tc.wPeriodMin);
         return -1;
     }
 
@@ -702,6 +707,7 @@ static void win32_stop_timer(struct qemu_alarm_timer *t)
     if (hTimer) {
         DeleteTimerQueueTimer(NULL, hTimer, NULL);
     }
+    timeEndPeriod(mm_tc.wPeriodMin);
 }
 
 static void win32_rearm_timer(struct qemu_alarm_timer *t,

Paolo