Hello everyone.
When I use gdb to trace qemu-xen-traditional， I have a little doubt
about host_alarm_handler. I already understand that it can implement
a dynamic tick, through tickless to save CPU cost. However, I found
that the following code has never run when I use qemu-xen-traditional
with xen(See attachment master.cfg).
if (env) {
/* stop the currently executing cpu because a timer occured */
cpu_interrupt(env, CPU_INTERRUPT_EXIT);
}
So I wonder if this code is useful when I use xen?
Moreover, I use this following function host_alarm_handler_empty
instead of host_alarm_handler as SIGALRM signal handler. Then I change
dynticks_timer from one-shot timer to period timer, and set
ev.sigev_notify = SIGEV_NONE when I create dynticks_timer (See
attachment period_timer.patch). I found that no problem except for usb
mouse slowness.
static void host_alarm_handler_empty(int host_signum)
{
return;
}
Finally, I use the following bash command to send the SIGALRM signal
to qemu-dm at 1ms intervals, the usb mouse also recovers fluency. I
can't understand how SIGALRM works, because SIGALRM just call
host_alarm_handler_empty function?
# QEMU_PID=`pgrep qemu-dm`; while true; do kill -s SIGALRM $QEMU_PID;
sleep 0.001; done
I would appreciate it if anyone could provide me some ideas.
-------------------------------------------------------------
Thanks,
Lu
diff --git a/vl.c b/vl.c
index f9c4d7e..105ce6e 100644
--- a/vl.c
+++ b/vl.c
@@ -1340,6 +1340,11 @@ static int timer_load(QEMUFile *f, void *opaque, int version_id)
void CALLBACK host_alarm_handler(UINT uTimerID, UINT uMsg,
DWORD_PTR dwUser, DWORD_PTR dw1, DWORD_PTR dw2)
#else
+static void host_alarm_handler_empty(int host_signum)
+{
+ return;
+}
+
static void host_alarm_handler(int host_signum)
#endif
{
@@ -1571,15 +1576,15 @@ static int dynticks_start_timer(struct qemu_alarm_timer *t)
struct sigevent ev = { { 0 } };
timer_t host_timer;
struct sigaction act;
+ struct itimerspec timeout;
sigfillset(&act.sa_mask);
act.sa_flags = 0;
- act.sa_handler = host_alarm_handler;
+ act.sa_handler = host_alarm_handler_empty;
sigaction(SIGALRM, &act, NULL);
- ev.sigev_notify = SIGEV_SIGNAL;
- ev.sigev_signo = SIGALRM;
+ ev.sigev_notify = SIGEV_NONE;
if (timer_create(CLOCK_REALTIME, &ev, &host_timer)) {
perror("timer_create");
@@ -1589,6 +1594,11 @@ static int dynticks_start_timer(struct qemu_alarm_timer *t)
return -1;
}
+ timeout.it_interval.tv_sec = 0;
+ timeout.it_interval.tv_nsec = 10000; /* 0 for one-shot timer */
+ timeout.it_value.tv_sec = 0;
+ timeout.it_value.tv_nsec = 10000;
+ timer_settime(host_timer, 0 /* RELATIVE */, &timeout, NULL);
t->priv = (void *)(long)host_timer;
@@ -1604,6 +1614,7 @@ static void dynticks_stop_timer(struct qemu_alarm_timer *t)
static void dynticks_rearm_timer(struct qemu_alarm_timer *t)
{
+ return;
timer_t host_timer = (timer_t)(long)t->priv;
struct itimerspec timeout;
int64_t nearest_delta_us = INT64_MAX;
master.cfg
Description: Binary data
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