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

[Gleb Natapov]

On Thu, Apr 25, 2013 at 12:28:35AM +0000, Joji Mekkattuparamban (joji) wrote:
> 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?
> 
Guest and host kernel should be at least 3.8. IIRC there is not QEMU
version dependency.

> 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.

--
                        Gleb.