From: Jeremy Fitzhardinge <jeremy@goop.org>
To: Dan Magenheimer <dan.magenheimer@oracle.com>
Cc: xen-devel@lists.xensource.com, "Dugger,
Donald D" <donald.d.dugger@intel.com>,
"Xu, Dongxiao" <dongxiao.xu@intel.com>,
Keir Fraser <keir.fraser@eu.citrix.com>,
"Nakajima, Jun" <jun.nakajima@intel.com>,
"Zhang, Xiantao" <xiantao.zhang@intel.com>
Subject: Re: RE: Saving/Restoring IA32_TSC_AUX MSR
Date: Sun, 13 Dec 2009 10:59:09 -0800 [thread overview]
Message-ID: <4B25397D.6010907@goop.org> (raw)
In-Reply-To: <7cecbafe-f4d4-410f-a3c0-6972c102e6c2@default>
On 12/13/09 10:06, Dan Magenheimer wrote:
> I agree there are some cases where the TSC_AUX value
> set by a guest OS may be useful. But ensuring that its
> is always useful (NEVER incorrect) requires too many restrictions,
> such as pinning.
>
At least with respect to Linux guests [*], this objection to rdtscp is
moot, because if it isn't present then Linux will fall back to another
mechanism which is always present. Guest usermode will get the same
info, good/bad/misleading/whatever, either way; rdtscp can't make it
worse. The only question is whether specifically adding rdtscp/TSC_AUX
support adds any overall improvement.
(* I don't know if any other rdtscp-users attempt to put NUMA or other
physical topology info into TSC_AUX. If they just stick to
setting/using the cpu number, then they will get a net win from rdtscp.)
J
next prev parent reply other threads:[~2009-12-13 18:59 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-12-09 16:41 Saving/Restoring IA32_TSC_AUX MSR Nakajima, Jun
2009-12-09 16:59 ` Dan Magenheimer
2009-12-09 17:07 ` Nakajima, Jun
2009-12-09 17:22 ` Dan Magenheimer
2009-12-10 11:21 ` Xu, Dongxiao
2009-12-10 15:49 ` Dan Magenheimer
2009-12-11 1:22 ` Xu, Dongxiao
2009-12-11 2:00 ` Dan Magenheimer
2009-12-11 8:03 ` Keir Fraser
2009-12-11 8:43 ` Zhang, Xiantao
2009-12-11 9:22 ` Keir Fraser
2009-12-11 15:09 ` Dan Magenheimer
2009-12-11 15:28 ` Xu, Dongxiao
2009-12-11 16:12 ` Dan Magenheimer
2009-12-11 18:38 ` Nakajima, Jun
2009-12-11 19:46 ` Dan Magenheimer
2009-12-11 18:20 ` Jeremy Fitzhardinge
2009-12-11 18:35 ` Dan Magenheimer
2009-12-11 18:50 ` Jeremy Fitzhardinge
2009-12-11 19:29 ` Nakajima, Jun
2009-12-11 22:23 ` Dan Magenheimer
2009-12-11 22:58 ` Nakajima, Jun
2009-12-11 23:30 ` Dan Magenheimer
2009-12-11 23:44 ` Xu, Dongxiao
2009-12-12 0:09 ` Dan Magenheimer
2009-12-12 0:30 ` Xu, Dongxiao
2009-12-13 9:17 ` Zhang, Xiantao
2009-12-13 18:06 ` Dan Magenheimer
2009-12-13 18:59 ` Jeremy Fitzhardinge [this message]
2009-12-14 6:33 ` Xu, Dongxiao
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