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xen-ppc-devel
Re: [XenPPC] Profiling in xen – ppc considerations
Jimi Xenidis wrote:
...
There really very little Linux work to do here. We need:
1. An hcall that turn the performance monitor on for the domain
2. Save and restore the relevant registers for any domain that is has
it turned on.
3. Turn it off for domains that have it disabled.
you can see the hcall being setup here:
arch/powerpc/platforms/pseries/setup.c pSeries_setup_arch 322
ppc_md.enable_pmcs = pseries_lpar_enable_pmcs;
...
I have evaluated all three items you listed above and I think to know
now what to do to implement them in detail. I will post a refined
version of your list after I have clarified the last open thing. You
suggested to use the hcall to enable performance monitoring and I looked
at the definition. The hcall currently contains a lot of information
like perf granularity, function pointer, ...
Currently I expect to need only to set a interdomain valid flag telling
xen "there is some profiling in progress" and optional a per domain flag
"this one is currently profiling" via an hcall for the first step of the
implementation. Because the guest can write all performance special
purpose registers xen needs only this flag to know if it has to
store/recover the perfmon registers.
We will need to restore MSR0/1,MSRA, PMC also for non-profiling guests
in context switch from a profiling one to non profiling guests, because
of that the easiest first implementation is something like the following
in context_switch().
...
if (perf_mon_in_use) {
save/restore MSR0/1,MSRA,PMC's
}
...
This will become more sophisticated in future but I currently expect
that we will not need the function pointer or profiling granularity
there for guest sampling. The only thing I currently expect for the
function pointer is to tell xen the place where to report hypervisor
samples in one of the next implementation steps.
Should/Can I use this complex hcall to set that simple flag e.g. by
skipping all other attributes or do we need a new one?
--
Grüsse / regards,
Christian Ehrhardt
IBM Linux Technology Center, Open Virtualization
+49 7031/16-3385
Ehrhardt@xxxxxxxxxxxxxxxxxxx
Ehrhardt@xxxxxxxxxx
IBM Deutschland Entwicklung GmbH
Vorsitzender des Aufsichtsrats: Johann Weihen
Geschäftsführung: Herbert Kircher
Sitz der Gesellschaft: Böblingen
Registergericht: Amtsgericht Stuttgart, HRB 243294
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