From: Jan Beulich <jbeulich@suse.com>
To: "Roger Pau Monné" <roger.pau@citrix.com>,
"Igor Druzhinin" <igor.druzhinin@citrix.com>
Cc: xen-devel@lists.xenproject.org, wl@xen.org, andrew.cooper3@citrix.com
Subject: Re: [Xen-devel] [PATCH] x86/time: update TSC stamp on restore from deep C-state
Date: Thu, 16 Jan 2020 10:38:10 +0100 [thread overview]
Message-ID: <b7a410db-5305-dc52-775b-88f07740bf5a@suse.com> (raw)
In-Reply-To: <20200116093354.GP11756@Air-de-Roger>
On 16.01.2020 10:33, Roger Pau Monné wrote:
> On Wed, Jan 15, 2020 at 05:21:16PM +0100, Jan Beulich wrote:
>> On 15.01.2020 14:44, Roger Pau Monné wrote:
>>> On Wed, Jan 15, 2020 at 01:49:22PM +0100, Jan Beulich wrote:
>>>> What I'm then worried about is too
>>>> little progress observable by guests. The PV time protocol
>>>> ought to be fine in this regard (and consumers of raw TSC values
>>>> are on their own anyway), but wouldn't you need to update TSC
>>>> offsets of HVM guests in order to compensate for the elapsed
>>>> time?
>>>
>>> That will be done when the HVM vCPU gets scheduled in as part of the
>>> update_vcpu_system_time call AFAICT. cstate_restore_tsc will always be
>>> called with the idle vCPU context, and hence there's always going to
>>> be a vCPU switch before scheduling anything else.
>>
>> Which step would this be? All I see is a call to hvm_scale_tsc().
>> In time.c only tsc_set_info() calls hvm_set_tsc_offset().
>
> My bad, I've mistaken the scaling with the offset.
>
> Accounting for the offset in update_vcpu_system_time seems quite
> more complicated that just updating the TSC here, so:
>
> Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
And then (preferably with "deep" dropped from the description,
if you, Igor, agree, and which can be done while committing)
Acked-by: Jan Beulich <jbeulich@suse.com>
Jan
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next prev parent reply other threads:[~2020-01-16 9:38 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-14 19:36 [Xen-devel] [PATCH] x86/time: update TSC stamp on restore from deep C-state Igor Druzhinin
2020-01-15 9:47 ` Roger Pau Monné
2020-01-15 11:40 ` Jan Beulich
2020-01-15 11:53 ` Roger Pau Monné
2020-01-15 12:49 ` Jan Beulich
2020-01-15 13:44 ` Roger Pau Monné
2020-01-15 16:21 ` Jan Beulich
2020-01-16 9:33 ` Roger Pau Monné
2020-01-16 9:38 ` Jan Beulich [this message]
2020-01-16 12:09 ` Igor Druzhinin
2020-01-16 12:25 ` Roger Pau Monné
2020-01-15 12:25 ` Igor Druzhinin
2020-01-15 12:31 ` Igor Druzhinin
2020-01-15 12:41 ` Jan Beulich
2020-01-15 12:36 ` Igor Druzhinin
2020-01-15 13:23 ` Roger Pau Monné
2020-01-15 14:45 ` Igor Druzhinin
2020-01-15 11:32 ` Jan Beulich
2020-01-15 12:28 ` Igor Druzhinin
2020-01-15 12:39 ` Jan Beulich
2020-01-15 12:47 ` Igor Druzhinin
2020-01-15 12:54 ` Jan Beulich
2020-01-15 14:55 ` Andrew Cooper
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