Re: [Qemu-devel] qemu vl.c

[Anders <mail@flac.kalibalik.dk>]

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Avi Kivity wrote:

> Time in grub is completely off, Linux calibrate_delay() complains, 
> 'sleep 1' doesn't return, but FC6 x86-64 boots.
> 
> (this is with your patch on top of the re-applied patch I reverted earlier).
> 

Now I have updated my kvm checkout, and I immediately got trouble 
booting the guest. So it seems something has changed since I made my 
first patch.

What I could find is that the "env" variable in host_alarm_handler() is 
always NULL now? Then the expiry flag has to be set outside of that 
conditional, or alarms will never expire.

Also, an optimization of the new rearming in qemu_mod_timer() is that it 
should not be done if we are currently running the expired timers. It 
will be done after all the running is over, anyway.

Attached is a reworked patch with these changes, it should apply against 
your kvm git master (i.e. do not re-apply the reverted one).


Anders.

[-- Attachment #2: kvm-reduce-rearm.diff --]
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diff --git a/qemu/vl.c b/qemu/vl.c
index 28c5df4..000df7e 100644
--- a/qemu/vl.c
+++ b/qemu/vl.c
@@ -850,6 +850,7 @@ struct qemu_alarm_timer {
 };
 
 #define ALARM_FLAG_DYNTICKS  0x1
+#define ALARM_FLAG_EXPIRED   0x2
 
 static inline int alarm_has_dynticks(struct qemu_alarm_timer *t)
 {
@@ -1061,6 +1062,12 @@ void qemu_mod_timer(QEMUTimer *ts, int64_t expire_time)
     ts->expire_time = expire_time;
     ts->next = *pt;
     *pt = ts;
+
+    /* Rearm if necessary  */
+    if ((alarm_timer->flags & ALARM_FLAG_EXPIRED) == 0
+        && pt == &active_timers[ts->clock->type]) {
+        qemu_rearm_alarm_timer(alarm_timer);
+    }
 }
 
 int qemu_timer_pending(QEMUTimer *ts)
@@ -1095,7 +1102,6 @@ static void qemu_run_timers(QEMUTimer **ptimer_head, int64_t current_time)
         /* run the callback (the timer list can be modified) */
         ts->cb(ts->opaque);
     }
-    qemu_rearm_alarm_timer(alarm_timer);
 }
 
 int64_t qemu_get_clock(QEMUClock *clock)
@@ -1215,6 +1221,8 @@ static void host_alarm_handler(int host_signum)
 #endif
         CPUState *env = next_cpu;
 
+        alarm_timer->flags |= ALARM_FLAG_EXPIRED;
+
         if (env) {
             /* stop the currently executing cpu because a timer occured */
             cpu_interrupt(env, CPU_INTERRUPT_EXIT);
@@ -7726,6 +7734,11 @@ void main_loop_wait(int timeout)
     qemu_run_timers(&active_timers[QEMU_TIMER_REALTIME],
                     qemu_get_clock(rt_clock));
 
+    if (alarm_timer->flags & ALARM_FLAG_EXPIRED) {
+        alarm_timer->flags &= ~(ALARM_FLAG_EXPIRED);
+        qemu_rearm_alarm_timer(alarm_timer);
+    }
+
     /* Check bottom-halves last in case any of the earlier events triggered
        them.  */
     qemu_bh_poll();