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cpus: reset throttle_thread_scheduled after sleep 

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 <felipe@nutanix.com>
Signed-off-by: Malcolm Crossley <malcolm@nutanix.com>
Message-Id: <1495229390-18909-1-git-send-email-felipe@nutanix.com>
Acked-by: Jason J. Herne <jjherne@linux.vnet.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Felipe Franciosi 2017-05-19 22:29:50 +01:00 committed by Paolo Bonzini
parent d870cfdea5
commit 90bb0c0421
1 changed files with 1 additions and 1 deletions
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2
cpus.c
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@ -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)