Currently, the throttle_thread_scheduled flag is reset back to 0 before sleeping (as part of the throttling logic). Given that throttle_timer (well, any timer) may tick with a slight delay, it so happens that under heavy throttling (ie. close or on CPU_THROTTLE_PCT_MAX) the tick may schedule a further cpu_throttle_thread() work item after the flag reset, but before the previous sleep completed. This results on the vCPU thread sleeping continuously for potentially several seconds in a row.
The chances of that happening can be drastically minimised by resetting the flag after the sleep. Signed-off-by: Felipe Franciosi <fel...@nutanix.com> Signed-off-by: Malcolm Crossley <malc...@nutanix.com> --- cpus.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/cpus.c b/cpus.c index 516e5cb..f42eebd 100644 --- a/cpus.c +++ b/cpus.c @@ -677,9 +677,9 @@ static void cpu_throttle_thread(CPUState *cpu, run_on_cpu_data opaque) sleeptime_ns = (long)(throttle_ratio * CPU_THROTTLE_TIMESLICE_NS); qemu_mutex_unlock_iothread(); - atomic_set(&cpu->throttle_thread_scheduled, 0); g_usleep(sleeptime_ns / 1000); /* Convert ns to us for usleep call */ qemu_mutex_lock_iothread(); + atomic_set(&cpu->throttle_thread_scheduled, 0); } static void cpu_throttle_timer_tick(void *opaque) -- 1.9.5