timers: fix stop/cont with -icount
Stop/cont commands are broken with -icount due to a deadlock. The
real problem is that the computation of timers_state.cpu_ticks_offset
makes no sense with -icount enabled: we set it to an icount clock value
in cpu_disable_ticks, and subtract a TSC (or similar, whatever
cpu_get_real_ticks happens to return) value in cpu_enable_ticks.
The fix is simple. timers_state.cpu_ticks_offset is only used
together with cpu_get_real_ticks, so we can use cpu_get_real_ticks
in cpu_disable_ticks. There is no need to update cpu_ticks_prev
at the time cpu_disable_ticks is called; instead, we can do it
the next time cpu_get_ticks is called.
The change to cpu_disable_ticks is the important part of the patch.
The rest modifies the code to always check timers_state.cpu_ticks_prev,
even when the ticks are not advancing (i.e. the VM is stopped). It also
makes a similar change to cpu_get_clock_locked, so that the code remains
similar for cpu_get_ticks and cpu_get_clock_locked.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-id: 1382977938-13844-1-git-send-email-pbonzini@redhat.com
Signed-off-by: Anthony Liguori <aliguori@amazon.com>
diff --git a/cpus.c b/cpus.c
index 912938c..01d128d 100644
--- a/cpus.c
+++ b/cpus.c
@@ -165,36 +165,38 @@
/* Caller must hold the BQL */
int64_t cpu_get_ticks(void)
{
+ int64_t ticks;
+
if (use_icount) {
return cpu_get_icount();
}
- if (!timers_state.cpu_ticks_enabled) {
- return timers_state.cpu_ticks_offset;
- } else {
- int64_t ticks;
- ticks = cpu_get_real_ticks();
- if (timers_state.cpu_ticks_prev > ticks) {
- /* Note: non increasing ticks may happen if the host uses
- software suspend */
- timers_state.cpu_ticks_offset += timers_state.cpu_ticks_prev - ticks;
- }
- timers_state.cpu_ticks_prev = ticks;
- return ticks + timers_state.cpu_ticks_offset;
+
+ ticks = timers_state.cpu_ticks_offset;
+ if (timers_state.cpu_ticks_enabled) {
+ ticks += cpu_get_real_ticks();
}
+
+ if (timers_state.cpu_ticks_prev > ticks) {
+ /* Note: non increasing ticks may happen if the host uses
+ software suspend */
+ timers_state.cpu_ticks_offset += timers_state.cpu_ticks_prev - ticks;
+ ticks = timers_state.cpu_ticks_prev;
+ }
+
+ timers_state.cpu_ticks_prev = ticks;
+ return ticks;
}
static int64_t cpu_get_clock_locked(void)
{
- int64_t ti;
+ int64_t ticks;
- if (!timers_state.cpu_ticks_enabled) {
- ti = timers_state.cpu_clock_offset;
- } else {
- ti = get_clock();
- ti += timers_state.cpu_clock_offset;
+ ticks = timers_state.cpu_clock_offset;
+ if (timers_state.cpu_ticks_enabled) {
+ ticks += get_clock();
}
- return ti;
+ return ticks;
}
/* return the host CPU monotonic timer and handle stop/restart */
@@ -235,7 +237,7 @@
/* Here, the really thing protected by seqlock is cpu_clock_offset. */
seqlock_write_lock(&timers_state.vm_clock_seqlock);
if (timers_state.cpu_ticks_enabled) {
- timers_state.cpu_ticks_offset = cpu_get_ticks();
+ timers_state.cpu_ticks_offset += cpu_get_real_ticks();
timers_state.cpu_clock_offset = cpu_get_clock_locked();
timers_state.cpu_ticks_enabled = 0;
}
