On Wed, 2018-06-27 at 10:05 -0700, Rodney W. Grimes wrote:
> >
> > On Wed, Jun 27, 2018 at 10:36 AM, Jung-uk Kim
> > wrote:
> >
> > >
> > > On 06/27/2018 03:14, Andriy Gapon wrote:
> > > >
> > > >
> > > > I
On Wed, Jun 27, 2018, 12:48 PM Alan Somers wrote:
> On Wed, Jun 27, 2018 at 10:36 AM, Jung-uk Kim wrote:
>
> > On 06/27/2018 03:14, Andriy Gapon wrote:
> > >
> > > It seems that TSC calibration in virtual machines sometimes can do more
> > harm
> > &
On 06/27/2018 13:05, Rodney W. Grimes wrote:
> There are several white papers, including one from VMWare about what
> they have done to help with the time keeping problems.
https://www.vmware.com/files/pdf/techpaper/Timekeeping-In-VirtualMachines.pdf
Jung-uk Kim
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> On Wed, Jun 27, 2018 at 10:36 AM, Jung-uk Kim wrote:
>
> > On 06/27/2018 03:14, Andriy Gapon wrote:
> > >
> > > It seems that TSC calibration in virtual machines sometimes can do more
> > harm
> > > than good. Should we default to trusting
On 06/27/2018 13:01, Ryan Stone wrote:
> I would guess that the calibration can fail because when running under
> the hypervisor, the FreeBSD guest code can be descheduled at the wrong
> time. As I recall, the current algorithm looks like:
>
> 1. Sample rdtsc
> 2. Use a fixed-frequency timer to b
I would guess that the calibration can fail because when running under
the hypervisor, the FreeBSD guest code can be descheduled at the wrong
time. As I recall, the current algorithm looks like:
1. Sample rdtsc
2. Use a fixed-frequency timer to busy-wait for exactly 1 second
3. Sample rdtsc again
On Wed, Jun 27, 2018 at 11:05 AM, Jung-uk Kim wrote:
> On 06/27/2018 12:47, Alan Somers wrote:
> > On Wed, Jun 27, 2018 at 10:36 AM, Jung-uk Kim > <mailto:j...@freebsd.org>> wrote:
> >
> > On 06/27/2018 03:14, Andriy Gapon wrote:
> > >
> >
On 06/27/2018 12:47, Alan Somers wrote:
> On Wed, Jun 27, 2018 at 10:36 AM, Jung-uk Kim <mailto:j...@freebsd.org>> wrote:
>
> On 06/27/2018 03:14, Andriy Gapon wrote:
> >
> > It seems that TSC calibration in virtual machines sometimes can do more
>
On Wed, Jun 27, 2018 at 10:36 AM, Jung-uk Kim wrote:
> On 06/27/2018 03:14, Andriy Gapon wrote:
> >
> > It seems that TSC calibration in virtual machines sometimes can do more
> harm
> > than good. Should we default to trusting the information provided by a
> hypervis
On 06/27/2018 03:14, Andriy Gapon wrote:
>
> It seems that TSC calibration in virtual machines sometimes can do more harm
> than good. Should we default to trusting the information provided by a
> hypervisor?
>
> Specifically, I am observing a problem on GCE instances wh
On 6/27/18 12:14 AM, Andriy Gapon wrote:
>
> It seems that TSC calibration in virtual machines sometimes can do more harm
> than good. Should we default to trusting the information provided by a
> hypervisor?
>
> Specifically, I am observing a problem on GCE instances wh
It seems that TSC calibration in virtual machines sometimes can do more harm
than good. Should we default to trusting the information provided by a
hypervisor?
Specifically, I am observing a problem on GCE instances where calibrated TSC
frequency is about 10% lower than advertised frequency
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