On 19/08/19 18:39, Paolo Bonzini wrote:
> On 15/08/19 11:13, Yury Kotov wrote:
>> Ping ping
>
> Hi,
>
> sorry for the delay, I was waiting for the 4.1 release.
>
> I would like to make a small change so that preemption of QEMU does not
> result in overly long sleeps. The following patch on top of yours computes
> the throttle-end time just once. Of course you can still be unlucky if
> you are preempted at the wrong time, but the window becomes much smaller.
The new unit test is hanging for me on aarch64-softmmu.
Paolo
> diff --git a/cpus.c b/cpus.c
> index d091dbd..d7e2145 100644
> --- a/cpus.c
> +++ b/cpus.c
> @@ -781,7 +781,7 @@ static void cpu_throttle_thread(CPUState *cpu,
> run_on_cpu_data opaque)
> {
> double pct;
> double throttle_ratio;
> - int64_t sleeptime_ns;
> + int64_t sleeptime_ns, end;
>
> if (!cpu_throttle_get_percentage()) {
> return;
> @@ -792,18 +792,17 @@ static void cpu_throttle_thread(CPUState *cpu,
> run_on_cpu_data opaque)
> /* Add 1ns to fix double's rounding error (like 0.9999999...) */
> sleeptime_ns = (int64_t)(throttle_ratio * CPU_THROTTLE_TIMESLICE_NS + 1);
>
> - while (sleeptime_ns >= SCALE_MS && !cpu->stop) {
> - int64_t start, end;
> - start = qemu_clock_get_ns(QEMU_CLOCK_REALTIME);
> - qemu_cond_timedwait(cpu->halt_cond, &qemu_global_mutex,
> - sleeptime_ns / SCALE_MS);
> - end = qemu_clock_get_ns(QEMU_CLOCK_REALTIME);
> - sleeptime_ns -= end - start;
> - }
> - if (sleeptime_ns >= SCALE_US && !cpu->stop) {
> - qemu_mutex_unlock_iothread();
> - g_usleep(sleeptime_ns / SCALE_US);
> - qemu_mutex_lock_iothread();
> + end = qemu_clock_get_ns(QEMU_CLOCK_REALTIME) + sleeptime_ns;
> + while (sleeptime_ns > 0 && !cpu->stop) {
> + if (sleeptime_ns > SCALE_MS) {
> + qemu_cond_timedwait(cpu->halt_cond, &qemu_global_mutex,
> + sleeptime_ns / SCALE_MS);
> + } else {
> + qemu_mutex_unlock_iothread();
> + g_usleep(sleeptime_ns / SCALE_US);
> + qemu_mutex_lock_iothread();
> + }
> + sleeptime_ns = end - qemu_clock_get_ns(QEMU_CLOCK_REALTIME);
> }
> atomic_set(&cpu->throttle_thread_scheduled, 0);
> }
>
