From: Keir Fraser <keir.xen@gmail.com>
To: "Tian, Kevin" <kevin.tian@intel.com>,
Dan Magenheimer <dan.magenheimer@oracle.com>,
Jan Beulich <JBeulich@novell.com>
Cc: xen devel <xen-devel@lists.xensource.com>
Subject: Re: [PATCH] x86, cpuidle: remove assertion on X86_FEATURE_TSC_RELIABLE
Date: Tue, 17 May 2011 08:58:16 +0100 [thread overview]
Message-ID: <C9F7E928.1A4A3%keir.xen@gmail.com> (raw)
In-Reply-To: <625BA99ED14B2D499DC4E29D8138F1505C9BBF8192@shsmsx502.ccr.corp.intel.com>
On 17/05/2011 01:50, "Tian, Kevin" <kevin.tian@intel.com> wrote:
>> IIRC, this is not true on a multi-socket motherboard. Even though each
>> socket
>> has NONSTOP_TSC, they are using different crystals, correct?
>>
>
> it's true that sockets may use different crystals, and NONSTOP_TSC has nothing
> to say
> synchronization among sockets/cores. So it really depends on how you define a
> 'reliable':
> is it reliable enough to be a Xen time source, or reliable enough to
> passthrough to the
> guest? I'll need to check current assumption and your previous discussions
> first before
> saying anything inappropriate. :-)
Yes, Dan is right, RELIABLE_TSC means something more than just NONSTOP_TSC
and CONSTANT_TSC. It means that:
1. TSCs do not stop in deep sleep (NONSTOP_TSC)
2. TSCs do not change rate with core frequency (CONSTANT_TSC)
3. Further, that all TSCs system wide run at the same rate at all times, in
perfect sync (not represented by any other cpu feature flag).
-- Keir
prev parent reply other threads:[~2011-05-17 7:58 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-05-13 2:45 [PATCH] x86, cpuidle: remove assertion on X86_FEATURE_TSC_RELIABLE Tian, Kevin
2011-05-13 5:55 ` Keir Fraser
2011-05-13 6:01 ` Tian, Kevin
2011-05-13 7:14 ` Jan Beulich
2011-05-13 7:28 ` Tian, Kevin
2011-05-13 8:17 ` Jan Beulich
2011-05-13 8:29 ` Keir Fraser
2011-05-13 8:49 ` Tian, Kevin
2011-05-13 9:15 ` Keir Fraser
2011-05-13 9:42 ` Jan Beulich
2011-05-17 0:51 ` Tian, Kevin
2011-05-13 17:16 ` Dan Magenheimer
2011-05-17 0:50 ` Tian, Kevin
2011-05-17 7:58 ` Keir Fraser [this message]
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