commit 84682834eb8f654da5e03a92930d80b8ae0d3065
author Paolo Bonzini <pbonzini@redhat.com> Thu Jun 09 13:10:25 2011 +0200
committer Anthony Liguori <aliguori@us.ibm.com> Sat Jul 23 11:18:57 2011 -0500
tree 3aeeec0738326f2e5e424820cbb3bab21fa855d6
parent 46daff13c854769bfa8c51e77719325ea0f47b1b

qemu-timer: change unix timer to dynticks

A timer that wakes up every millisecond puts a lot of stress on the
iothread.  The large amount of IPIs causes very high context switch
activity, making emulation slow and the UI unusable.  This is by the
way the same reason why the Windows timers were switched to dynticks.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Tested-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

qemu-timer.c

diff --git a/qemu-timer.c b/qemu-timer.c
index 72066c7..67c2974 100644
--- a/qemu-timer.c
+++ b/qemu-timer.c
@@ -218,6 +218,7 @@
 
 static int unix_start_timer(struct qemu_alarm_timer *t);
 static void unix_stop_timer(struct qemu_alarm_timer *t);
+static void unix_rearm_timer(struct qemu_alarm_timer *t);
 
 #ifdef __linux__
 
@@ -290,7 +291,7 @@
     {"dynticks", dynticks_start_timer,
      dynticks_stop_timer, dynticks_rearm_timer},
 #endif
-    {"unix", unix_start_timer, unix_stop_timer, NULL},
+    {"unix", unix_start_timer, unix_stop_timer, unix_rearm_timer},
 #else
     {"mmtimer", mm_start_timer, mm_stop_timer, NULL},
     {"mmtimer2", mm_start_timer, mm_stop_timer, mm_rearm_timer},
@@ -890,8 +891,6 @@
 static int unix_start_timer(struct qemu_alarm_timer *t)
 {
     struct sigaction act;
-    struct itimerval itv;
-    int err;
 
     /* timer signal */
     sigfillset(&act.sa_mask);
@@ -899,18 +898,35 @@
     act.sa_handler = host_alarm_handler;
 
     sigaction(SIGALRM, &act, NULL);
+    return 0;
+}
+
+static void unix_rearm_timer(struct qemu_alarm_timer *t)
+{
+    struct itimerval itv;
+    int64_t nearest_delta_ns = INT64_MAX;
+    int err;
+
+    assert(alarm_has_dynticks(t));
+    if (!active_timers[QEMU_CLOCK_REALTIME] &&
+        !active_timers[QEMU_CLOCK_VIRTUAL] &&
+        !active_timers[QEMU_CLOCK_HOST])
+        return;
+
+    nearest_delta_ns = qemu_next_alarm_deadline();
+    if (nearest_delta_ns < MIN_TIMER_REARM_NS)
+        nearest_delta_ns = MIN_TIMER_REARM_NS;
 
     itv.it_interval.tv_sec = 0;
-    /* for i386 kernel 2.6 to get 1 ms */
-    itv.it_interval.tv_usec = 999;
-    itv.it_value.tv_sec = 0;
-    itv.it_value.tv_usec = 10 * 1000;
-
+    itv.it_interval.tv_usec = 0; /* 0 for one-shot timer */
+    itv.it_value.tv_sec =  nearest_delta_ns / 1000000000;
+    itv.it_value.tv_usec = (nearest_delta_ns % 1000000000) / 1000;
     err = setitimer(ITIMER_REAL, &itv, NULL);
-    if (err)
-        return -1;
-
-    return 0;
+    if (err) {
+        perror("setitimer");
+        fprintf(stderr, "Internal timer error: aborting\n");
+        exit(1);
+    }
 }
 
 static void unix_stop_timer(struct qemu_alarm_timer *t)