On 20/09/2016 10:34, zhong...@sangfor.com.cn wrote: > yes, the full options on clock is > '-rtc driftfix=slew,clock=rt,base=localtime'
Good, then we should include a fixed patch that checks for clock=rt. Please remember to include the command-line options in the commit message. Thanks! Paolo > ------------------------------------------------------------------------ > zhong...@sangfor.com.cn > > > *From:* Paolo Bonzini <mailto:pbonz...@redhat.com> > *Date:* 2016-09-20 16:17 > *To:* zhong...@sangfor.com.cn <mailto:zhong...@sangfor.com.cn>; > qemu-devel <mailto:qemu-devel@nongnu.org> > *CC:* Michael S. Tsirkin <mailto:m...@redhat.com> > *Subject:* Re: [PATCH]MC146818 RTC: coordinate guest clock base to > destination host after migration > > > On 20/09/2016 09:19, zhong...@sangfor.com.cn wrote: > > qemu tracks guest time based on vector [base_rtc, last_update], in > which > > last_update stands for a monotonic tick which is actually uptime > of the host. > > But last_update is not a monotonic tick, it's basically gettimeofday > unless you're using the "-rtc clock=..." option. > > > +static void rtc_flush_time(RTCState *s) > > +{ > > + struct tm ret; > > + time_t guest_sec; > > + int64_t guest_nsec; > > + uint64_t guest_clock = qemu_clock_get_ns(rtc_clock); > > + > > + guest_nsec = s->base_rtc * NANOSECONDS_PER_SECOND > > + + guest_clock - s->last_update; > > + guest_sec = (guest_nsec + NANOSECONDS_PER_SECOND/2)/ > NANOSECONDS_PER_SECOND; > > + gmtime_r(&guest_sec, &ret); > > + > > + rtc_set_cmos(s, &ret); > > This should be just rtc_update_time(s). > > Similarly: > > > > > + rtc_get_time(s, &tm); > > + diff = mktimegm(&tm) - s->base_rtc; > > + assert(diff >= 0); > > + s->last_update = qemu_clock_get_ns(rtc_clock) > > + - diff * NANOSECONDS_PER_SECOND; > > This should be rtc_set_time. > > However, there are two problems with this approach. First, if you > migrate old QEMU to new QEMU, the new QEMU expects to have an up-to-date > s->base_rtc, while old QEMU provided an old QEMU. Second, every > migration will delay the RTC by a few tenths of a second. So the call > to rtc_set_time should be conditional on rtc_clock == > QEMU_CLOCK_REALTIME. > > Paolo >
