Re: [Xen-devel] RE: rdtsc: correctness vs performance on Xen (and KVM?)

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

On 02/09/2009 22:44, "Jeremy Fitzhardinge" <jeremy@xxxxxxxx> wrote:

> On 09/02/09 00:20, Keir Fraser wrote:
>> The problem is a bit easier with vsyscall potentially. For example, give
>> each thread its own vsyscall clock data area (easy?), updated by kernel
>> whenever the thread is scheduled, and increment a version counter, checked
>> before and after by the vsyscall operation.
>>   
> 
> Yes.  Perhaps the very simplest way would be to make the kernel update
> the pvclock version counter on context switch, the same way Xen does;
> that would allow the usermode vsyscall code to use exactly the same
> algorithm as the kernel code.  Would Xen cope with that?

Yes, that's basically how I would envision it working. The main missing
detail afaics is how to manage and access the required per-thread data.

 -- Keir



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