On 29/07/2017 14:35, Denis Plotnikov wrote:
> arch/x86/kernel/kvmclock.c | 14 ++++++++++++--
> arch/x86/kernel/tsc.c | 6 ++++++
> arch/x86/kvm/x86.c | 26 ++++++++++++++++++--------
> include/linux/clocksource.h | 3 +++
> include/linux/timekeeping.h | 2 ++
> kernel/time/timekeeping.c | 21 +++++++++++++++++++--
> 6 files changed, 60 insertions(+), 12 deletions(-)
This is pretty clean, thanks. Only it should be split in several patches:
- introducing read_with_cycles and using it in ktime_get_snapshot.
Looking at the code, the meaning of "cycles" is overloaded, so perhaps
rename it to read_clock_and_systime or something similar?
- introducing boot time in ktime_get_snapshot
- implementing kvm_clock_read_with_cycles (can be merged with patch 6)
- adding the cs_stable field to struct system_time_snapshot (see below,
maybe this can be merged with read_with_cycles)
- using ktime_get_snapshot in KVM (can be merged with patch 4?)
so that the timekeeping maintainer can comment on each new feature you
add to their code.
cs_stable is the part that I'm still a bit wary of; here are the doubts
I have:
- if you want stability, you can use the CLOCK_SOURCE_UNSTABLE flag; a
new callback shouldn't be needed (it's certainly not needed for TSC).
- the meaning of "stable" for kvmclock is not exactly the same as
clocksource_mark_unstable.
Maybe what we want is some kind of "bool cycles_valid", and then
read_clock_and_systime can return it:
if (clock->read_clock_and_systime) {
systime_snapshot->cycles_valid = clock->read_clock_and_systime(
&now, &systime_snapshot->cycles);
} else {
now = tk_clock_read(&tk->tkr_mono);
systime_snapshot->cycles_valid = true;
systime_snapshot->cycles = now;
}
? (This is honestly just a suggestion, which may be wrong depedning
on the answer to the two questions above).
Paolo
> systime_snapshot->cs_was_changed_seq = tk->cs_was_changed_seq;
> systime_snapshot->clock_was_set_seq = tk->clock_was_set_seq;
> base_real = ktime_add(tk->tkr_mono.base,
> tk_core.timekeeper.offs_real);
> base_raw = tk->tkr_raw.base;
> + base_boot = ktime_add(tk->tkr_mono.base,
> + tk_core.timekeeper.offs_boot);
> nsec_real = timekeeping_cycles_to_ns(&tk->tkr_mono, now);
> nsec_raw = timekeeping_cycles_to_ns(&tk->tkr_raw, now);
> } while (read_seqcount_retry(&tk_core.seq, seq));
>
> - systime_snapshot->cycles = now;
> systime_snapshot->real = ktime_add_ns(base_real, nsec_real);
> systime_snapshot->raw = ktime_add_ns(base_raw, nsec_raw);
> + systime_snapshot->boot = ktime_add_ns(base_boot, nsec_real);
> }
> EXPORT_SYMBOL_GPL(ktime_get_snapshot);
>
>
