Re: [RFC] Correct/fast timestamping in apps under Xen [1 of 4]: Reliable TSC

[Jeremy Fitzhardinge <jeremy@goop.org>]

On 10/09/09 19:36, Dan Magenheimer wrote:
> Very nice!
>
> One more measurement if you haven't already torn down
> your test environment:   If you are at xen-unstable tip,
> with tsc emulation on, please try something like:
>
> for i in {0..100}; do
> xm debug-key s; xm dmesg | tail; sleep 1;
> done
>
> to get an idea of the number of rdtsc's being
> done per second (and also divide by the number
> of cores so we have rdtsc's/sec/core).  This is
> of course unloaded, so if you have a favorite
> load to throw on it, that would be very interesting
> also.
>   

The kernel does about between 400k and 1.4M/sec, median around ~600k,
for a git pull (which I think is single-threaded), and about
200k-500k/sec for a kernel compile (-j4 on 2 vcpus).  Usermode is a much
lower rate; around 1000/sec for the kernel compile.

Baseline idle is around 1000/sec kernel, 10/sec user.

Also, my inline naked rdtsc benchmark shows that the emulated rdtsc is
taking around 465ns (vs 30, a 15x slowdown).

    J