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

[Gleb Natapov]

On Wed, May 15, 2013 at 08:40:25PM +0000, Joji Mekkattuparamban (joji) wrote:
> Hi Gleb,
> 
> On a related note, does Qemu have an option to emulate RDTSC?
> 
QEMU or KVM? With KVM guest executes RDTSC directly on CPU.

> Thanks,
> Joji.
> 
> -----Original Message-----
> From: Gleb Natapov [mailto:address@hidden 
> Sent: Wednesday, April 24, 2013 11:57 PM
> To: Joji Mekkattuparamban (joji)
> Cc: Marcelo Tosatti; address@hidden; address@hidden
> Subject: Re: [Qemu-devel] Para-Virtualized Clock Usage
> 
> 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.
> --
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--
                        Gleb.