RE: [Xen-devel] Time skew on HP DL785 (and possibly other boxes)

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

>From: Keir Fraser [mailto:keir.fraser@xxxxxxxxxxxxx] 
>Sent: 2009年4月5日 21:28
>
>On 05/04/2009 13:17, "Tian, Kevin" <kevin.tian@xxxxxxxxx> wrote:
>
>>> One concern I have however, is Intel's
>>> X86_FEATURE_CONSTANT_TSC logic. This
>>> was added by them to prevent TSCs from diverging due to Cx 
>deep sleep
>>> states, by observing that usually all TSCs will tick at the
>>> same exact rate,
>> 
>> Here one correction is, that constant tsc logic is introduced for
>> P-states instead of C-states, to have TSC always stepping in
>> constant pace on a given processor, regardless of whatever
>> opertion point is being requested by cpufreq governor. It
>> doesn't say anything that all TSCs tick at same rate however.
>
>Then changeset 18923 is indeed broken and should be reverted? 
>The problem is
>this changeset doesn't just affect the cases it is meant to 
>'fix' (usage of
>C states for CPUs without no-stop TSC). Apart from the fact it 
>can be broken
>for systems with that type of CPU as well, it's actually 
>enabled for any
>modern CPU (anything advertising the constant-tsc feature). Probably I
>shouldn't have checked in that patch in the first place.
>

How about making it a selectable option, instead of reversing
it completely?

Thanks,.
Kevin

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel