From: "Jan Beulich" <JBeulich@suse.com>
To: Joao Martins <joao.m.martins@oracle.com>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>,
Keir Fraser <keir@xen.org>,
xen-devel@lists.xen.org
Subject: Re: [PATCH v2 6/6] x86/time: implement PVCLOCK_TSC_STABLE_BIT
Date: Thu, 07 Apr 2016 15:32:12 -0600 [thread overview]
Message-ID: <5706DFEC02000078000E6023@prv-mh.provo.novell.com> (raw)
In-Reply-To: <5706CE81.6050407@oracle.com>
>>> On 07.04.16 at 23:17, <joao.m.martins@oracle.com> wrote:
>> > The main
>>> difference I see between both would be the base system time:
>>> read_platform_stime
>>> uses stime_platform_stamp as base, and computes a difference from the
>>> read_counter (i.e. rdtsc() ) with previously saved platform-wide stamp
>>> (platform_timer_stamp). get_s_time uses the stime_local_stamp (updated from
>>> stime_master_stamp on local_time_calibration) as base plus delta from
>>> rdtsc()
>>> with local_tsc_stamp. And since this is now all TSC, and TSC monotonically
>>> increase and is synchronized across CPUs, both calls would end up returning
>>> the
>>> same or a always up-to-date value, whether cpu_time have a larger gap or not
>>> from stime_platform_stamp. Unless the concern you are raising comes from the
>>> fact CPU 0 calibrates much sooner than the last calibrated CPU, as opposed
>>> to
>>> roughly at the same time with std_rendezvous?
>>
>> In a way, yes. I'm concerned by the two time stamps no longer
>> being obtained at (almost) the same time. If that's not having
>> any bad consequences, the better.
>
> I don't think there would be bad consequences as both timestamps correspond
> to the same time reference - thus returning always the latest system time
> irrespective of the gap between both stamps.
>
> If you prefer I can go back with my initial approach (v1, with std_rendezvous)
> to have both timestamps closely updated. And later (post-release?) revisit
> the introduction of nop_rendezvous. Perhaps this way is more reasonable?
Since the new mode need to be actively asked for, I don't think
that's necessary.
Jan
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prev parent reply other threads:[~2016-04-07 21:32 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-29 13:44 [PATCH v2 0/6] x86/time: PVCLOCK_TSC_STABLE_BIT support Joao Martins
2016-03-29 13:44 ` [PATCH v2 1/6] public/xen.h: add flags field to vcpu_time_info Joao Martins
2016-03-30 15:49 ` Ian Jackson
2016-03-30 16:33 ` Joao Martins
2016-03-31 7:09 ` Jan Beulich
2016-03-31 7:13 ` Jan Beulich
2016-03-31 11:04 ` Joao Martins
2016-04-05 10:16 ` Jan Beulich
2016-04-05 10:59 ` Joao Martins
2016-03-29 13:44 ` [PATCH v2 2/6] x86/time: refactor init_platform_time() Joao Martins
2016-04-01 16:10 ` Konrad Rzeszutek Wilk
2016-04-01 18:26 ` Joao Martins
2016-04-05 10:09 ` Jan Beulich
2016-04-05 10:55 ` Joao Martins
2016-04-05 11:16 ` Jan Beulich
2016-03-29 13:44 ` [PATCH v2 3/6] x86/time: implement tsc as clocksource Joao Martins
2016-03-29 17:39 ` Konrad Rzeszutek Wilk
2016-03-29 17:52 ` Joao Martins
2016-04-01 16:43 ` Konrad Rzeszutek Wilk
2016-04-01 18:38 ` Joao Martins
2016-04-01 18:45 ` Konrad Rzeszutek Wilk
2016-04-03 18:47 ` Joao Martins
2016-04-05 10:43 ` Jan Beulich
2016-04-05 14:56 ` Joao Martins
2016-04-05 15:12 ` Jan Beulich
2016-04-05 17:07 ` Joao Martins
2016-03-29 13:44 ` [PATCH v2 4/6] x86/time: streamline platform time init on plt_init() Joao Martins
2016-04-05 11:46 ` Jan Beulich
2016-04-05 15:12 ` Joao Martins
2016-04-05 15:22 ` Jan Beulich
2016-04-05 17:17 ` Joao Martins
2016-03-29 13:44 ` [PATCH v2 5/6] x86/time: refactor read_platform_stime() Joao Martins
2016-04-01 18:32 ` Konrad Rzeszutek Wilk
2016-04-05 11:52 ` Jan Beulich
2016-04-05 15:22 ` Joao Martins
2016-04-05 15:26 ` Jan Beulich
2016-04-05 17:08 ` Joao Martins
2016-03-29 13:44 ` [PATCH v2 6/6] x86/time: implement PVCLOCK_TSC_STABLE_BIT Joao Martins
2016-04-05 12:22 ` Jan Beulich
2016-04-05 21:34 ` Joao Martins
2016-04-07 15:58 ` Jan Beulich
2016-04-07 21:17 ` Joao Martins
2016-04-07 21:32 ` Jan Beulich [this message]
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