IIUC the throttle idea is that: we split a CPU_THROTTLE_TIMESLICE_NS
time slice into two parts - one for vcpu, one for throttle thread (which
will suspend the thread by a sleep). However current algorithm on
calculating the working piece and sleeping piece is strange.
Assume a 99% throttle, what we want is to merely stop vcpu from running,
but the old logic will just first let the vcpu run for a very long
time (which is "CPU_THROTTLE_TIMESLICE_NS / (1-pct)" = 1 second) before
doing anything else.
Fixing it up to the simplest but imho accurate logic.
CC: Paolo Bonzini <pbonz...@redhat.com>
CC: Richard Henderson <r...@twiddle.net>
CC: Jason J. Herne <jjhe...@linux.vnet.ibm.com>
Signed-off-by: Peter Xu <pet...@redhat.com>
---
cpus.c | 6 ++----
1 file changed, 2 insertions(+), 4 deletions(-)
diff --git a/cpus.c b/cpus.c
index 167d961..7976ce4 100644
--- a/cpus.c
+++ b/cpus.c
@@ -633,7 +633,6 @@ static const VMStateDescription vmstate_timers = {
static void cpu_throttle_thread(CPUState *cpu, run_on_cpu_data opaque)
{
double pct;
- double throttle_ratio;
long sleeptime_ns;
if (!cpu_throttle_get_percentage()) {
@@ -641,8 +640,7 @@ static void cpu_throttle_thread(CPUState *cpu,
run_on_cpu_data opaque)
}
pct = (double)cpu_throttle_get_percentage()/100;
- throttle_ratio = pct / (1 - pct);
- sleeptime_ns = (long)(throttle_ratio * CPU_THROTTLE_TIMESLICE_NS);
+ sleeptime_ns = (long)((1 - pct) * CPU_THROTTLE_TIMESLICE_NS);
qemu_mutex_unlock_iothread();
atomic_set(&cpu->throttle_thread_scheduled, 0);
@@ -668,7 +666,7 @@ static void cpu_throttle_timer_tick(void *opaque)
pct = (double)cpu_throttle_get_percentage()/100;
timer_mod(throttle_timer, qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL_RT) +
- CPU_THROTTLE_TIMESLICE_NS / (1-pct));
+ CPU_THROTTLE_TIMESLICE_NS * pct);
}
void cpu_throttle_set(int new_throttle_pct)
--
2.7.4
