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

[Stefan Weil]

Am 19.09.2012 09:26, schrieb Paolo Bonzini:

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 <pbonz...@redhat.com>
Cc: Jan Kiszka <jan.kis...@siemens.com>
Signed-off-by: Anthony Liguori <aligu...@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

The win32 timer still works when these modifications were applied.
What are they good for?

Stefan