Re: [Xen-devel] [RFC] Correct/fast timestamping in apps under Xen [1 of 4]: Reliable TSC

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

On 08/10/2009 07:45, "Keir Fraser" <keir.fraser@xxxxxxxxxxxxx> wrote:

>> 1) On (Intel, maybe later AMD) systems where this
>>    bit is set, the mechanisms enabled by the
>>    Xen consistent_tscs boot option should be enabled
>>    automatically for Xen.
>> 2) The time_calibration_tsc_rendezvous loop in
>>    timer.c could/should be rewritten or removed
>>    and certainly should NOT write_tsc().
>> 
>> Keir, I know you are very sensitive around
>> this code, so thought I'd check before messing
>> with it.  Or feel free to do it yourself.
> 
> Feel free to make a patch.

At least, make a patch for (1). I don't think (2) can be easily removed in
all cases. For example, Intel's method for rate-invariant TSC which stops on
deep sleeps does involve rewriting TSC values to forcibly keep them in sync.
Perhaps change code to never write_tsc() just in the case of TSC_RELIABLE,
or whatever you call it? Or perhaps just do (1) for now.

 -- Keir



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