On 01/02/2018 08:47, Gonglei wrote: > As windows guest use rtc as the clock source device, > and access rtc frequently. Let's move the rtc memory > region outside BQL to decrease overhead for windows guests. > > strace -tt -p $1 -c -o result_$1.log & > sleep $2 > pid=$(pidof strace) > kill $pid > cat result_$1.log > > Before appling this change: > > % time seconds usecs/call calls errors syscall > ------ ----------- ----------- --------- --------- ---------------- > 93.87 0.119070 30 4000 ppoll > 3.27 0.004148 2 2038 ioctl > 2.66 0.003370 2 2014 futex > 0.09 0.000113 1 106 read > 0.09 0.000109 1 104 io_getevents > 0.02 0.000029 1 30 poll > 0.00 0.000000 0 1 write > ------ ----------- ----------- --------- --------- ---------------- > 100.00 0.126839 8293 total > > After appling the change: > > % time seconds usecs/call calls errors syscall > ------ ----------- ----------- --------- --------- ---------------- > 92.86 0.067441 16 4094 ppoll > 4.85 0.003522 2 2136 ioctl > 1.17 0.000850 4 189 futex > 0.54 0.000395 2 202 read > 0.52 0.000379 2 202 io_getevents > 0.05 0.000037 1 30 poll > ------ ----------- ----------- --------- --------- ---------------- > 100.00 0.072624 6853 total > > The futex call number decreases ~90.6% on an idle windows 7 guest. > > Signed-off-by: Gonglei <arei.gong...@huawei.com> > --- > hw/timer/mc146818rtc.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/hw/timer/mc146818rtc.c b/hw/timer/mc146818rtc.c > index 35a05a6..d9d99c5 100644 > --- a/hw/timer/mc146818rtc.c > +++ b/hw/timer/mc146818rtc.c > @@ -986,6 +986,7 @@ static void rtc_realizefn(DeviceState *dev, Error **errp) > qemu_register_suspend_notifier(&s->suspend_notifier); > > memory_region_init_io(&s->io, OBJECT(s), &cmos_ops, s, "rtc", 2); > + memory_region_clear_global_locking(&s->io); > isa_register_ioport(isadev, &s->io, base); > > qdev_set_legacy_instance_id(dev, base, 3); >
This is not enough, you need to add a new lock or something like that. Otherwise two vCPUs can access the RTC together and make a mess. Paolo
