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From: Joao Martins <joao.m.martins@oracle.com>
To: Jan Beulich <JBeulich@suse.com>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>,
	Dario Faggioli <dario.faggioli@citrix.com>,
	Wei Liu <wei.liu2@citrix.com>,
	xen-devel <xen-devel@lists.xenproject.org>
Subject: Re: [PATCH] x86/time: use correct (local) time stamp in constant-TSC calibration fast path
Date: Fri, 10 Jun 2016 18:07:59 +0100	[thread overview]
Message-ID: <575AF3EF.1060405@oracle.com> (raw)
In-Reply-To: <575AA4A402000078000F3E2F@prv-mh.provo.novell.com>

On 06/10/2016 10:29 AM, Jan Beulich wrote:
>>>> On 10.06.16 at 08:59, <JBeulich@suse.com> wrote:
>> Actually, since local time gets seeded from platform time in
>> init_percpu_time(), I don't think we can do away with
>> maintaining platform time.
>
Yeah, I agree. But the case of my previous message was towards
improvement potential of the rendezvous after this patch (for
the fast path). Platform time overflow could be another example
but probably a bit borderline as certain clocksources have very
short intervals.

> And it looks like this seeding is where much of the remaining backwards
> deltas are coming from: While on local_time_calibration()'s slow path
> we use the platform time as reference (and hence the seeding is fine),
> on the fast path we don't, and hence using the platform time in
> init_percpu_time() to initialize local stime introduces a discontinuity.

I'll do some testing too on your patch that's addressing this on Monday (today
is an holiday in my country).

Joao

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  reply	other threads:[~2016-06-10 17:07 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-06-09 12:01 Jan Beulich
2016-06-09 12:10 ` Andrew Cooper
2016-06-09 12:11 ` Joao Martins
2016-06-09 12:57   ` Jan Beulich
2016-06-09 15:00     ` Joao Martins
2016-06-09 15:52       ` Jan Beulich
2016-06-09 18:19         ` Joao Martins
2016-06-10  6:59           ` Jan Beulich
2016-06-10  9:29             ` Jan Beulich
2016-06-10 17:07               ` Joao Martins [this message]
2016-06-09 12:12 ` Wei Liu

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