Re: [Qemu-devel] Para-Virtualized Clock Usage

[Joji Mekkattuparamban (joji)]

Thank you Gleb and Marcelo. I will migrate the API using gettimeofday.

Is there any dependency on the QEMU or the Guest? If the host supports pvclock 
and the guest invokes gettimeofday, would the pvclock be automatically used? Or 
do I require a patch in either the Qemu or the guest kernel?

Thanks!
Joji.

-----Original Message-----
From: Marcelo Tosatti [mailto:address@hidden 
Sent: Wednesday, April 24, 2013 1:28 AM
To: Gleb Natapov
Cc: Joji Mekkattuparamban (joji); address@hidden; address@hidden
Subject: Re: [Qemu-devel] Para-Virtualized Clock Usage

On Tue, Apr 23, 2013 at 08:52:16AM +0300, Gleb Natapov wrote:
> On Mon, Apr 22, 2013 at 04:58:01PM +0000, Joji Mekkattuparamban (joji) wrote:
> > Greetings,
> > 
> > I have a SMP guest application, running on the 2.6.27 Linux kernel. The 
> > application, originally written for bare metal, makes extensive use of the 
> > TSC, by directly invoking rdtsc from the user space for timestamp purposes. 
> > While running on KVM (RHEL version 6.3), we are running into TSC issues on 
> > some hardware. As a solution, I am considering migrating to the pvclock. I 
> > am wondering if there is an example for migrating from TSC to the pvclock. 
> > Any pointers?
> > 
> Wrong list, you should ask KVM (copied). Recent kernels have pvclock 
> vdso support which means that gettimeofday() uses it without entering 
> the kernel. Marcelo?
> 
> --
>                       Gleb.

Converting application to make use of gettimeofday() should be the best way to 
make use of pvclock, yes.