From: Andrew Cooper <andrew.cooper3@citrix.com>
To: Paul Durrant <paul@xen.org>, <xen-devel@lists.xenproject.org>
Cc: "Paul Durrant" <pdurrant@amazon.com>,
"Jan Beulich" <jbeulich@suse.com>,
"Ian Jackson" <iwj@xenproject.org>, "Wei Liu" <wl@xen.org>,
"George Dunlap" <george.dunlap@citrix.com>,
"Julien Grall" <julien@xen.org>,
"Stefano Stabellini" <sstabellini@kernel.org>,
"Roger Pau Monné" <roger.pau@citrix.com>
Subject: Re: [PATCH v10 06/11] x86/time: add a domain context record for tsc_info...
Date: Mon, 25 Jan 2021 19:24:06 +0000 [thread overview]
Message-ID: <b781829e-25b1-2d9d-2cad-29ac551f1194@citrix.com> (raw)
In-Reply-To: <20201008185735.29875-7-paul@xen.org>
On 08/10/2020 19:57, Paul Durrant wrote:
> +The record body contains the following fields:
> +
> +| Field | Description |
> +|---------------|-----------------------------------------------|
> +| `mode` | 0x00000000: Default (emulate if necessary) |
> +| | 0x00000001: Always emulate |
> +| | 0x00000002: Never emulate |
> +| | |
> +| `khz` | The TSC frequency in kHz |
> +| | |
> +| `nsec` | Elapsed time in nanoseconds |
> +| | |
> +| `incarnation` | Incarnation (counter indicating how many |
> +| | times the TSC value has been set) |
It is how many set_tsc_info() (hyper)calls have been made, not how many
times the guest has written to the TSC MSR.
That said, it is totally useless now that PVRDTSCP mode has gone, other
than the fact that it appears in guest CPUID as an approximation of "how
many times has this domain been migrated".
I.e. its a number you'll want to actively squash in your usecase.
I'm not sure whether to suggest dropping the field entirely, or not. I
highly doubt any user exists - IIRC, it was specifically for PVRDTSCP
userspace to notice that the frequency may have changed, and to
re-adjust its calculations.
> diff --git a/xen/include/public/save.h b/xen/include/public/save.h
> index bccbaadd0b..86881864cf 100644
> --- a/xen/include/public/save.h
> +++ b/xen/include/public/save.h
> @@ -50,6 +50,7 @@ enum {
> DOMAIN_CONTEXT_END,
> DOMAIN_CONTEXT_START,
> DOMAIN_CONTEXT_SHARED_INFO,
> + DOMAIN_CONTEXT_TSC_INFO,
At a minimum, this wants an /* x86 only */ comment. Possibly an X86 infix.
~Andrew
next prev parent reply other threads:[~2021-01-25 19:24 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-08 18:57 [PATCH v10 00/11] domain context infrastructure Paul Durrant
2020-10-08 18:57 ` [PATCH v10 01/11] docs / include: introduce a new framework for 'domain context' records Paul Durrant
2020-10-19 13:46 ` Jan Beulich
2021-01-25 18:25 ` Andrew Cooper
2021-01-26 8:55 ` Jan Beulich
2021-01-25 18:18 ` Andrew Cooper
2021-01-26 9:31 ` Jan Beulich
2020-10-08 18:57 ` [PATCH v10 02/11] xen: introduce implementation of save/restore of 'domain context' Paul Durrant
2020-10-19 14:07 ` Jan Beulich
2021-01-25 18:36 ` Andrew Cooper
2020-10-08 18:57 ` [PATCH v10 03/11] xen/common/domctl: introduce XEN_DOMCTL_get/set_domain_context Paul Durrant
2020-10-19 14:30 ` Jan Beulich
2020-10-19 15:06 ` Jan Beulich
2020-10-08 18:57 ` [PATCH v10 04/11] tools/misc: add xen-domctx to present domain context Paul Durrant
2020-10-08 18:57 ` [PATCH v10 05/11] common/domain: add a domain context record for shared_info Paul Durrant
2020-10-19 15:25 ` Jan Beulich
2021-01-25 19:11 ` Andrew Cooper
2020-10-08 18:57 ` [PATCH v10 06/11] x86/time: add a domain context record for tsc_info Paul Durrant
2021-01-25 19:24 ` Andrew Cooper [this message]
2020-10-08 18:57 ` [PATCH v10 07/11] docs/specs: add missing definitions to libxc-migration-stream Paul Durrant
2021-01-25 19:28 ` Andrew Cooper
2020-10-08 18:57 ` [PATCH v10 08/11] docs / tools: specify migration v4 to include DOMAIN_CONTEXT Paul Durrant
2021-01-25 19:43 ` Andrew Cooper
2020-10-08 18:57 ` [PATCH v10 09/11] tools/python: modify libxc.py to verify v4 stream Paul Durrant
2021-01-25 19:45 ` Andrew Cooper
2020-10-08 18:57 ` [PATCH v10 10/11] tools/libs/guest: add code to restore a v4 libxc stream Paul Durrant
2021-01-25 20:04 ` Andrew Cooper
2020-10-08 18:57 ` [PATCH v10 11/11] tools/libs/guest: add code to save " Paul Durrant
2021-01-25 20:11 ` Andrew Cooper
2021-01-25 20:15 ` [PATCH v10 00/11] domain context infrastructure Andrew Cooper
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