[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] 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/ > > _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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