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xen-devel
RE: [Xen-devel] reading time value in dom0 and domU kernels
> Hi Keir/All,
> If I want to measure time at the application level, is there
> any API available? can gettimeofday in domU give me real time value?
On xen linux, gettimeofday will return an accurate 'wall clock' time
value
Ian
> On 4/9/06, Keir Fraser <Keir.Fraser@xxxxxxxxxxxx> wrote:
>
>
> On 9 Apr 2006, at 16:19, sanjay kumar wrote:
>
> > Hi Folks,
> > I want to calculate latency in transferring a buffer
> from domU kernel
> > to dom0 kernel and vice versa. for that I need a time
> 'flavour' (cycle
> > counter time?) which reads the same in dom0 and domU.
> Could someone
> > please let me know if cycle counter time is the right
> time to use? if
> > not then which one (system time or wall clock time)?
> Also could
> > someone please tell me how to read to read this timer value.
> >
> > if I use rdtsc() in both dom0 and domU, will it give
> me the same time
> > value?
>
> It should be close enough as Xen attempts to
> synchronise the TSCs of
> all CPUs during boot and on most x86 platforms the TSCs will not
> diverge.
>
> If you're measuring in the kernel then something like
> 'sched_clock()'
> will get you system time in nanoseconds. That would be slightly
> preferable as system time is actively synchronised
> across all domains.
> With TSC you are winging it a tiny bit (although it's
> usually an okay
> strategy on x86).
>
> -- Keir
>
>
>
>
>
>
> --
> ----------------------
> PhD Student, Georgia Tech
> http://www.cc.gatech.edu/~ksanjay/
>
>
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