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xen-devel
Re: [Xen-devel] reading time value in dom0 and domU kernels
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
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