[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH v3 5/6] xen/arm: introduce xen_read_wallclock
On Wed, 11 Nov 2015, Arnd Bergmann wrote: > On Wednesday 11 November 2015 16:51:35 Stefano Stabellini wrote: > > +static void xen_read_wallclock(struct timespec64 *ts) > > +{ > > + u32 version; > > + u64 delta; > > + struct timespec64 now; > > + struct shared_info *s = HYPERVISOR_shared_info; > > + struct pvclock_wall_clock *wall_clock = &(s->wc); > > + > > + /* get wallclock at system boot */ > > + do { > > + version = wall_clock->version; > > + rmb(); /* fetch version before time */ > > + now.tv_sec = ((uint64_t)wall_clock->sec_hi << 32) | > > wall_clock->sec; > > + now.tv_nsec = wall_clock->nsec; > > + rmb(); /* fetch time before checking version */ > > + } while ((wall_clock->version & 1) || (version != > > wall_clock->version)); > > + > > + /* time since system boot */ > > + delta = ktime_get_ns(); > > + delta += now.tv_sec * (u64)NSEC_PER_SEC + now.tv_nsec; > > + > > + *ts = ns_to_timespec64(delta); > > +} > > Looks correct to me and better than the previous versions, but you are still > converting from timespec64 to nanoseconds and back. While I previously > recommended going all the way to nanoseconds here, I guess this you > can even avoid the ns_to_timespec64() if you stay within timespec64 > domain and replace the last lines with > > ktime_get_ts64(&ts_monotonic); > *ts = timespec64_add(now, ts_monotonic); > > which avoids both the multiplication and division. Much better, I'll do that. Thanks for the suggestion! _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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