* Jason J. Herne (jjhe...@linux.vnet.ibm.com) wrote: > On 05/19/2017 05:29 PM, Felipe Franciosi wrote: > > 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) > > > > This seems to make sense to me. > > Acked-by: Jason J. Herne <jjhe...@linux.vnet.ibm.com> > > I'm CC'ing Juan, Amit and David as they are all active in the migration area > and may have > opinions on this. Juan and David were also reviewers for the original > series.
The description is interesting and sounds reasonable; it'll be interesting to see what difference it makes to the autoconverge behaviour for those workloads that need this level of throttle. Dave > -- > -- Jason J. Herne (jjhe...@linux.vnet.ibm.com) > -- Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
