From: Richard Cochran <richardcochran@gmail.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
Radim Krcmar <rkrcmar@redhat.com>,
Miroslav Lichvar <mlichvar@redhat.com>
Subject: Re: [patch 4/5] PTP: add PTP_SYS_OFFSET emulation via cross timestamps infrastructure
Date: Tue, 24 Jan 2017 06:43:03 +0100 [thread overview]
Message-ID: <20170124054302.GB1906@localhost.localdomain> (raw)
In-Reply-To: <e7ab90e9-6cfd-a926-196b-0018184d6f92@redhat.com>
On Mon, Jan 23, 2017 at 08:44:53PM +0100, Paolo Bonzini wrote:
> If you just implement getclock64 the PTP_SYS_OFFSET output:
>
> device clock | |sample2| |sample4| |sample6| ...
> -------------------------------------------------------------
> realtime clock |sample1| |sample3| |sample5|
>
> has a very large distance between samples on the same line (about 1 us),
> and I think it is too noisy for userspace to make sense of the output.
One microsecond is not too bad at all. The PCIe devices have
intervals of 5-6 usec, and the result is quite usable, certainly
better than generic NTP.
> Marcelo's patch then produces fake realtime clock samples that, however,
> let chrony derive the cross timestamps that KVM produced in the first
> place. The outcome is really great accuracy compared to previous
> versions of the patch, often just +/- 2 or 3 nanoseconds.
Why can't chrony learn about PTP_SYS_OFFSET_PRECISE?
Thanks,
Richard
next prev parent reply other threads:[~2017-01-24 5:43 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-01-20 12:20 [patch 0/5] KVM virtual PTP driver (v3) Marcelo Tosatti
2017-01-20 12:20 ` [patch 1/5] KVM: x86: provide realtime host clock via vsyscall notifiers Marcelo Tosatti
2017-01-20 12:20 ` [patch 2/5] KVM: x86: add KVM_HC_CLOCK_OFFSET hypercall Marcelo Tosatti
2017-01-20 12:20 ` [patch 3/5] kvmclock: export kvmclock clocksource pointer Marcelo Tosatti
2017-01-20 12:55 ` Paolo Bonzini
2017-01-20 12:20 ` [patch 4/5] PTP: add PTP_SYS_OFFSET emulation via cross timestamps infrastructure Marcelo Tosatti
2017-01-20 12:55 ` Paolo Bonzini
2017-01-20 13:07 ` Marcelo Tosatti
2017-01-20 13:36 ` Paolo Bonzini
2017-01-20 13:52 ` Marcelo Tosatti
2017-01-20 14:02 ` Radim Krcmar
2017-01-20 14:23 ` Paolo Bonzini
2017-01-20 14:31 ` Miroslav Lichvar
2017-01-20 18:30 ` Radim Krcmar
2017-01-20 20:25 ` Richard Cochran
2017-01-23 13:19 ` Marcelo Tosatti
2017-01-23 18:44 ` Richard Cochran
2017-01-23 19:44 ` Paolo Bonzini
2017-01-24 5:43 ` Richard Cochran [this message]
2017-01-24 11:23 ` Marcelo Tosatti
2017-01-24 11:35 ` Richard Cochran
2017-01-23 23:06 ` Marcelo Tosatti
2017-01-24 5:32 ` Richard Cochran
2017-01-24 8:15 ` Miroslav Lichvar
2017-01-20 12:20 ` [patch 5/5] PTP: add kvm PTP driver Marcelo Tosatti
2017-01-20 12:58 ` Paolo Bonzini
2017-01-20 13:11 ` Marcelo Tosatti
2017-01-20 14:12 ` Radim Krcmar
2017-01-20 14:20 ` Radim Krcmar
2017-01-20 15:00 ` Marcelo Tosatti
2017-01-20 17:11 ` Paolo Bonzini
2017-01-20 18:08 ` Radim Krcmar
2017-01-20 19:10 ` Marcelo Tosatti
2017-01-21 8:02 ` Paolo Bonzini
2017-01-20 13:10 ` [patch 0/5] KVM virtual PTP driver (v3) Paolo Bonzini
-- strict thread matches above, loose matches on Subject: below --
2017-01-20 14:51 [patch 0/5] KVM virtual PTP driver (v4) Marcelo Tosatti
2017-01-20 14:51 ` [patch 4/5] PTP: add PTP_SYS_OFFSET emulation via cross timestamps infrastructure Marcelo Tosatti
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