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Re: [Qemu-devel] qemu vl.c

From: Anders
Subject: Re: [Qemu-devel] qemu vl.c
Date: Wed, 19 Dec 2007 00:57:19 +0100
User-agent: Thunderbird (X11/20071022)

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).

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_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) */
-    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)
         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)
+    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.  */

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