On Fri, Jan 13, 2017 at 05:28:09PM +0100, Radim Krcmar wrote: > 2017-01-13 13:34-0200, Marcelo Tosatti: > > On Fri, Jan 13, 2017 at 04:18:04PM +0100, Radim Krcmar wrote: > >> 2017-01-13 10:01-0200, Marcelo Tosatti: > >> > Expose the realtime host clock and save the TSC value > >> > used for the clock calculation. > >> > > >> > Signed-off-by: Marcelo Tosatti <mtosa...@redhat.com> > >> > > >> > --- > >> > arch/x86/kvm/x86.c | 38 ++++++++++++++++++++++++++++++++++++++ > >> > 1 file changed, 38 insertions(+) > >> > > >> > Index: kvm-ptpdriver/arch/x86/kvm/x86.c > >> > =================================================================== > >> > --- kvm-ptpdriver.orig/arch/x86/kvm/x86.c 2017-01-13 > >> > 08:59:03.015895353 -0200 > >> > +++ kvm-ptpdriver/arch/x86/kvm/x86.c 2017-01-13 09:04:46.581415259 > >> > -0200 > >> > @@ -1139,6 +1139,8 @@ > >> > > >> > u64 boot_ns; > >> > u64 nsec_base; > >> > + u64 wall_time_sec; > >> > + u64 wall_time_snsec; > >> > >> The leading "s" in "snsec" looks like a copy-paste residue. > > > > Just copying the userspace vsyscall interface. > > Oh, so the "s" means "sub-" for sub-nanosecond precision.
It only counts nanoseconds, how can it be sub nanosecond precise? > >> > }; > >> > > >> > static struct pvclock_gtod_data pvclock_gtod_data; > >> > @@ -1162,6 +1164,9 @@ > >> > vdata->boot_ns = boot_ns; > >> > vdata->nsec_base = tk->tkr_mono.xtime_nsec; > >> > > >> > + vdata->wall_time_sec = tk->xtime_sec; > >> > + vdata->wall_time_snsec = tk->tkr_mono.xtime_nsec; > >> > >> Using tk->tkr_mono offsets for real time seems wrong -- what happens if > >> the real time is half a second shifted from monotonic time? > > > > Both the userspace vsyscall interface and getnstimeofday > > use it for realtime clock. > > > > Monotonic clock adds the offset: > > > > vdata->monotonic_time_snsec = tk->tkr_mono.xtime_nsec > > + > > ((u64)tk->wall_to_monotonic.tv_nsec > > << tk->tkr_mono.shift); > > I see, thanks. Makes me wonder why our monotonic time is correct then, > but that is problably thanks to boot_ns. The actual starting point of the system_timestamp part of kvmclock does not matter, all it matters is that it counts in nanoseconds. > >> If it's ok, then vdata->nsec_base == vdata->wall_time_snsec, so we don't > >> need it. > > > > Just copying the userspace vsyscall interface. > > > > Do you actually want to change the "s" and unify wall_time_snsec with > > nsec_base? > > The "s" isn't important, even though I don't think we do anything that > would justify it, but make use just 8 bytes for both. Unified. > Renaming nsec_base is ok, but I'm not sure what tk->tkr_mono.xtime_nsec > is anymore. Is the nsec part of tk->xtime_sec. See accumulate_nsecs_to_secs (which is called from the timer interrupt handler). /** * struct timekeeper - Structure holding internal timekeeping values. * @tkr_mono: The readout base structure for CLOCK_MONOTONIC * @tkr_raw: The readout base structure for * CLOCK_MONOTONIC_RAW * @xtime_sec: Current CLOCK_REALTIME time in seconds * @ktime_sec: Current CLOCK_MONOTONIC time in seconds * @wall_to_monotonic: CLOCK_REALTIME to CLOCK_MONOTONIC offset * @offs_real: Offset clock monotonic -> clock realtime * @offs_boot: Offset clock monotonic -> clock boottime * @offs_tai: Offset clock monotonic -> clock tai * @tai_offset: The current UTC to TAI offset in seconds
