From: Jeremy Fitzhardinge <jeremy@goop.org>
To: Keir Fraser <keir.fraser@eu.citrix.com>
Cc: Dan Magenheimer <dan.magenheimer@oracle.com>,
"Xen-Devel (E-mail)" <xen-devel@lists.xensource.com>,
"Dong, Eddie" <eddie.dong@intel.com>,
John Levon <levon@movementarian.org>,
Ian Pratt <Ian.Pratt@eu.citrix.com>,
"Zhang, Xiantao" <xiantao.zhang@intel.com>
Subject: Re: Re: TSC scaling and softtsc reprise, and PROPOSAL
Date: Tue, 04 Aug 2009 17:05:49 -0700 [thread overview]
Message-ID: <4A78CCDD.9090205@goop.org> (raw)
In-Reply-To: <C68F298A.104C0%keir.fraser@eu.citrix.com>
On 07/24/09 01:04, Keir Fraser wrote:
> Okay, so the issue you are worried about is not specific to Xen. So how is
> native Linux tackling this, for example?
>
Linux will use the tsc where possible, but regularly assesses its
perceived accuracy and will move to a different clocksource if the tsc
appears to the playing up. I don't think it ever assumes the tsc is
synced between CPU/cores.
It allows rdtsc from usermode, but it is generally considered to be very
buggy and ill-defined behaviour. It makes no attempt to make usermode
rdtsc in any way meaningful. The exception is the vgettimeofday
vsyscall which does Xen-like timekeeping, in which it gets the tsc,cpu
tuple atomically, then scales it with timing parameters from the kernel.
J
next prev parent reply other threads:[~2009-08-05 0:05 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-07-20 17:05 TSC scaling and softtsc reprise, and PROPOSAL Dan Magenheimer
2009-07-20 17:14 ` Keir Fraser
2009-07-20 20:02 ` Dan Magenheimer
2009-07-20 21:02 ` Keir Fraser
2009-07-20 23:52 ` Dan Magenheimer
2009-07-22 5:05 ` Zhang, Xiantao
2009-07-23 13:24 ` Dan Magenheimer
2009-07-23 14:54 ` Ian Pratt
2009-07-23 15:18 ` Dan Magenheimer
2009-07-23 15:29 ` Keir Fraser
2009-07-23 16:39 ` Dan Magenheimer
2009-07-24 8:04 ` Keir Fraser
2009-07-24 14:47 ` Dan Magenheimer
2009-08-05 0:05 ` Jeremy Fitzhardinge [this message]
2009-08-05 5:35 ` Tian, Kevin
2009-08-06 21:13 ` Dan Magenheimer
2009-08-06 21:41 ` Dan Magenheimer
2009-07-23 15:45 ` Keir Fraser
2009-07-23 16:45 ` Dan Magenheimer
2009-07-27 14:47 ` Dan Magenheimer
2009-07-27 14:55 ` Keir Fraser
2009-07-27 17:25 ` Dan Magenheimer
2009-07-27 19:55 ` Keir Fraser
2009-07-27 22:14 ` Dan Magenheimer
2009-07-27 22:39 ` Keir Fraser
2009-08-03 20:19 ` Dan Magenheimer
2009-07-28 1:46 ` Zhang, Xiantao
2009-07-28 14:45 ` Dan Magenheimer
2009-07-28 15:00 ` Keir Fraser
2009-07-28 15:46 ` Dan Magenheimer
2009-07-28 15:58 ` Keir Fraser
2009-07-28 18:15 ` Dan Magenheimer
2009-07-28 18:43 ` Keir Fraser
2009-07-28 19:10 ` Dan Magenheimer
2009-07-28 18:48 ` Keir Fraser
2009-07-28 0:55 ` Zhang, Xiantao
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