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From: Andrew Cooper <andrew.cooper3@citrix.com>
To: Jan Beulich <JBeulich@suse.com>
Cc: xen-devel <xen-devel@lists.xenproject.org>,
	Dario Faggioli <dario.faggioli@citrix.com>,
	Joao Martins <joao.m.martins@oracle.com>
Subject: Re: [PATCH 5/8] x86/time: correctly honor late clearing of TSC related feature flags
Date: Mon, 4 Jul 2016 16:39:32 +0100	[thread overview]
Message-ID: <ffb1cb8d-d4a5-a56e-a3d6-9ac0812b33b5@citrix.com> (raw)
In-Reply-To: <576825C602000078000F6F96@prv-mh.provo.novell.com>

On 20/06/16 16:20, Jan Beulich wrote:
>>>> On 20.06.16 at 16:32, <andrew.cooper3@citrix.com> wrote:
>> On 15/06/16 11:28, Jan Beulich wrote:
>>> --- a/xen/arch/x86/time.c
>>> +++ b/xen/arch/x86/time.c
>>> @@ -1358,6 +1358,24 @@ static void time_calibration(void *unuse
>>>                       &r, 1);
>>>  }
>>>  
>>> +void __init clear_tsc_cap(unsigned int feature)
>>> +{
>>> +    void (*rendezvous_fn)(void *) = time_calibration_std_rendezvous;
>> This should read time_calibration_rendezvous_fn rather than assuming
>> time_calibration_std_rendezvous.
>>
>> Otherwise, there is a risk that it could be reset back to
>> time_calibration_std_rendezvous.
> But that's the purpose: We may need to switch back.

Under what circumstances could we ever move from re-syncing back to not
re-syncing?

Even in a scenario with pcpu hotplug, where we lose the final pcpu which
was causing re-syncing, we don't know that one of the intermediate pcpus
hasn't gone and come back, with a different TSC base.

~Andrew

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  reply	other threads:[~2016-07-04 15:40 UTC|newest]

Thread overview: 39+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-06-15  9:50 [PATCH 0/8] x86/time: improve cross-CPU clock monotonicity (and more) Jan Beulich
2016-06-15 10:26 ` [PATCH 1/8] " Jan Beulich
2016-06-15 10:32   ` Jan Beulich
2016-06-15 22:51   ` Joao Martins
2016-06-16  8:27     ` Jan Beulich
2016-06-16 20:27       ` Joao Martins
2016-06-17  7:32         ` Jan Beulich
2016-06-21 12:05           ` Joao Martins
2016-06-21 12:28             ` Jan Beulich
2016-06-21 13:57               ` Joao Martins
2016-08-02 19:30   ` Andrew Cooper
2016-06-15 10:26 ` [PATCH 2/8] x86: also generate assembler usable equates for synthesized features Jan Beulich
2016-06-20 12:50   ` Andrew Cooper
2016-06-15 10:27 ` [PATCH 3/8] x86/time: introduce and use rdtsc_ordered() Jan Beulich
2016-06-20 12:59   ` Andrew Cooper
2016-06-20 13:06     ` Jan Beulich
2016-06-20 13:07       ` Andrew Cooper
2016-07-11 11:39     ` Dario Faggioli
2016-06-15 10:28 ` [PATCH 4/8] x86/time: calibrate TSC against platform timer Jan Beulich
2016-06-20 14:20   ` Andrew Cooper
2016-06-20 15:19     ` Jan Beulich
2016-08-02 19:25       ` Andrew Cooper
2016-08-03  9:32         ` Jan Beulich
2016-06-15 10:28 ` [PATCH 5/8] x86/time: correctly honor late clearing of TSC related feature flags Jan Beulich
2016-06-20 14:32   ` Andrew Cooper
2016-06-20 15:20     ` Jan Beulich
2016-07-04 15:39       ` Andrew Cooper [this message]
2016-07-04 15:53         ` Jan Beulich
2016-08-02 19:08           ` Andrew Cooper
2016-08-03  9:43             ` Jan Beulich
2016-08-31 13:42               ` Andrew Cooper
2016-08-31 14:03                 ` Jan Beulich
2016-06-15 10:29 ` [PATCH 6/8] x86/time: support 32-bit wide ACPI PM timer Jan Beulich
2016-07-04 15:40   ` Andrew Cooper
2016-06-15 10:30 ` [PATCH 7/8] x86/time: fold recurring code Jan Beulich
2016-07-04 15:43   ` Andrew Cooper
2016-06-15 10:30 ` [PATCH 8/8] x86/time: group time stamps into a structure Jan Beulich
2016-07-04 15:57   ` Andrew Cooper
2016-07-01  7:44 ` Ping: [PATCH 0/8] x86/time: improve cross-CPU clock monotonicity (and more) Jan Beulich

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