From: Boris Ostrovsky <boris.ostrovsky@amd.com>
To: Keir Fraser <keir@xen.org>
Cc: wei.huang2@amd.com, Jan Beulich <JBeulich@suse.com>,
xen-devel <xen-devel@lists.xen.org>
Subject: Re: [PATCH] svm: Do not intercept RDTCS(P) when TSC scaling is supported by hardware
Date: Fri, 20 Apr 2012 11:27:18 -0400 [thread overview]
Message-ID: <4F918056.3040200@amd.com> (raw)
In-Reply-To: <CBB6E0C6.3E84F%keir@xen.org>
On 04/20/12 04:45, Keir Fraser wrote:
> On 20/04/2012 09:15, "Jan Beulich"<JBeulich@suse.com> wrote:
>
>>> svm: Do not intercept RDTCS(P) when TSC scaling is supported by hardware
>>>
>>> When running in TSC_MODE_ALWAYS_EMULATE mode on processors that support
>>> TSC scaling we don't need to intercept RDTSC/RDTSCP instructions.
>>
>> While the patch itself looks fine, I'm having difficulty to connect the
>> mentioning of TSC_MODE_ALWAYS_EMULATE to it - afaics all modes
>> are affected as long as they result in d->arch.vtsc to be set.
>
> I think the real point of this patch is they *never* want to trap and
> emulate RDTSC on these newer processors.
Right. Mentioning TSC_MODE_ALWAYS_EMULATE explicitly wasn't probably a
particularly good idea.
The reason I did that was because with TSC_MODE_DEFAULT guests (at least
Linux guests) typically don't use TSC since TSC ends up being declared
non-invariant.
-boris
next prev parent reply other threads:[~2012-04-20 15:27 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-04-20 2:21 [PATCH] svm: Do not intercept RDTCS(P) when TSC scaling is supported by hardware Boris Ostrovsky
2012-04-20 3:57 ` Huang2, Wei
2012-04-20 8:05 ` Keir Fraser
2012-04-20 8:14 ` Keir Fraser
2012-04-20 15:06 ` Huang2, Wei
2012-04-20 16:56 ` Keir Fraser
2012-04-20 15:02 ` Dan Magenheimer
2012-04-20 16:20 ` Wei Huang
2012-04-20 17:25 ` Dan Magenheimer
2012-04-20 8:15 ` Jan Beulich
2012-04-20 8:45 ` Keir Fraser
2012-04-20 15:27 ` Boris Ostrovsky [this message]
2012-04-25 9:27 ` Jan Beulich
2012-04-25 15:01 ` Dan Magenheimer
2012-04-25 15:51 ` Jan Beulich
2012-04-25 16:05 ` Dan Magenheimer
2012-04-25 16:04 ` Wei Huang
2012-04-25 17:14 ` Keir Fraser
2012-04-25 20:07 ` Boris Ostrovsky
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