> -----Original Message----- > From: Paolo Bonzini [mailto:pbonz...@redhat.com] > Sent: Thursday, February 01, 2018 10:24 PM > To: Gonglei (Arei); qemu-devel@nongnu.org > Cc: Huangweidong (C) > Subject: Re: [PATCH] rtc: placing RTC memory region outside BQL > > 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. >
Hi Paolo, Yes, that's true, although I have not encountered any problems yet. Let me enhance it in v2. Thanks, -Gonglei
