lkml.org 
[lkml]   [2007]   [Oct]   [29]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] raise tsc clocksource rating
Ingo Molnar wrote:
> * Zachary Amsden <zach@vmware.com> wrote:
>
>
>> On Mon, 2007-10-29 at 20:10 -0300, Glauber de Oliveira Costa wrote:
>>
>>> From: Glauber de Oliveira Costa <glauber@t60.localdomain>
>>>
>>> tsc is very good time source (when it does not have drifts, does not
>>> change it's frequency, i.e. when it works), so it should have its rating
>>> raised to a value greater than, or equal 400.
>>>
>>> Since it's being a tendency among paravirt clocksources to use values
>>> around 400, we should declare tsc as even better: So we use 500.
>>>
>> Why is the TSC better than a paravirt clocksource? In our case this
>> is definitely inaccurate. Paravirt clocksources should be preferred
>> to TSC, and both must be made available in hardware for platforms
>> which do not support paravirt.
>>
>
> if it's inaccurate why are you exposing it to the guest then? Native
> only uses the TSC if it's safe and accurate to do so.
>

It is used as part of the Xen clocksource as a short term extrapolator,
with correction parameters supplied by the hypervisor. It should never
be used directly.

J
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2007-10-29 23:55    [W:0.067 / U:4.108 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site