Messages in this thread | | | Subject | Re: [PATCH] KVM: x86/xen: improve accuracy of Xen timers | From | David Woodhouse <> | Date | Tue, 31 Oct 2023 19:45:02 +0000 |
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On Mon, 2023-10-30 at 15:50 +0000, David Woodhouse wrote: > > +static int do_monotonic(s64 *t, u64 *tsc_timestamp) > +{ > + struct pvclock_gtod_data *gtod = &pvclock_gtod_data; > + unsigned long seq; > + int mode; > + u64 ns; > + > + do { > + seq = read_seqcount_begin(>od->seq); > + ns = gtod->clock.base_cycles; > + ns += vgettsc(>od->clock, tsc_timestamp, &mode); > + ns >>= gtod->clock.shift; > + ns += ktime_to_ns(ktime_add(gtod->clock.offset, > gtod->offs_boot)); > + } while (unlikely(read_seqcount_retry(>od->seq, seq))); > + *t = ns; > + > + return mode; > +} > +
Hrm, that's basically cargo-culted from do_monotonic_raw() immediately above it. Should it be adding gtod->offs_boot?
Empirically the answer would appear to be 'no'. When gtod->offs_boot is non-zero, I see kvm_get_monotonic_and_clockread() returning values which are precisely that far in advance of what ktime_get() reports.
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