From: Paolo Bonzini <pbonzini@redhat.com>
To: Denis Plotnikov <dplotnikov@virtuozzo.com>,
rkrcmar@redhat.com, kvm@vger.kernel.org
Cc: rkagan@virtuozzo.com, den@virtuozzo.com, svt-core@lists.sw.ru
Subject: Re: [PATCH v3 2/6] KVM: x86: switch to masterclock update using timekeeper functionality
Date: Mon, 31 Jul 2017 16:20:07 +0200 [thread overview]
Message-ID: <aa7786d5-22d2-b759-9934-04260ffc87c6@redhat.com> (raw)
In-Reply-To: <1501331711-12961-3-git-send-email-dplotnikov@virtuozzo.com>
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);
>
>
next prev parent reply other threads:[~2017-07-31 14:20 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-07-29 12:35 [PATCH v3 0/6] make L2's kvm-clock stable, get rid of pvclock_gtod Denis Plotnikov
2017-07-29 12:35 ` [PATCH v3 1/6] pvclock: add parameter to store cycles stamp to pvclock reading function Denis Plotnikov
2017-07-31 14:08 ` Paolo Bonzini
2017-07-29 12:35 ` [PATCH v3 2/6] KVM: x86: switch to masterclock update using timekeeper functionality Denis Plotnikov
2017-07-31 14:20 ` Paolo Bonzini [this message]
2017-08-01 9:30 ` Denis Plotnikov
2017-08-01 10:03 ` Paolo Bonzini
2017-08-01 10:16 ` Paolo Bonzini
2017-08-01 12:11 ` Denis Plotnikov
2017-08-01 12:28 ` Denis Plotnikov
2017-08-01 12:41 ` Paolo Bonzini
2017-08-01 12:46 ` Denis Plotnikov
2017-08-01 17:47 ` Radim Krčmář
2017-07-29 12:35 ` [PATCH v3 3/6] timekeeper: add clocksource change notifier Denis Plotnikov
2017-07-29 12:35 ` [PATCH v3 4/6] KVM: x86: remove not used pvclock_gtod_copy Denis Plotnikov
2017-07-29 12:35 ` [PATCH v3 5/6] pvclock: add clocksource change notification on changing of tsc stable bit Denis Plotnikov
2017-07-31 14:21 ` Paolo Bonzini
2017-07-29 12:35 ` [PATCH v3 6/6] kvmclock: add the clocksource stability querying function Denis Plotnikov
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