[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH v2 6/7] xen/arm: introduce xen_read_wallclock
On Tuesday 10 November 2015 11:57:54 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)); > + > + delta = arch_timer_read_counter() * (u64)NSEC_PER_SEC; > + do_div(delta, arch_timer_get_rate()); /* time since system boot */ > + delta += now.tv_sec * (u64)NSEC_PER_SEC + now.tv_nsec; > + > + now.tv_nsec = do_div(delta, NSEC_PER_SEC); > + now.tv_sec = delta; > + > + set_normalized_timespec64(ts, now.tv_sec, now.tv_nsec); > + > +} Instead of the two do_div(), I would do the entire calculation in terms of nanoseconds and then call ns_to_timespec64() in the end instead of set_normalized_timespec64(). That is just an optimization though, your version looks correct as well. Arnd _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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