[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 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. Arnd _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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