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From: William Cohen on 18 Mar 2010 18:00
* Ingo Molnar <mingo(a)xxxxxxxx> wrote:
> * Avi Kivity <avi(a)xxxxxxxxxx> wrote:
> > Monitoring guests from the host is useful for kvm developers, but less so
> > for users.
> Guest space profiling is easy, and 'perf kvm' is not about that. (plain 'perf'
> will work if a proper paravirt channel is opened to the host)
> I think you might have misunderstood the purpose and role of the 'perf kvm'
> patch here? 'perf kvm' is aimed at KVM developers: it is them who improve KVM
> code, not guest kernel users.
The software performance events work fine in a KVM guest. Do the hardware performance events work in KVM guest environment? Last time I looked the results for the hardware counters were not sane. The values were seemingly random numbers. Something like the following.
Performance counter stats for 'ls':
3.427434 task-clock-msecs # 0.046 CPUs
2 context-switches # 0.001 M/sec
0 CPU-migrations # 0.000 M/sec
218 page-faults # 0.064 M/sec
140737488355327 cycles # 41062056440.861 M/sec
68825777242116 instructions # 0.489 IPC
68825777242117 branches # 20080846849.893 M/sec
68825777242118 branch-misses # 100.000 %
<not counted> cache-references
<not counted> cache-misses
The guest image is using 2.6.34-0.10.rc1.git0.fc14.it68 kernel and the host is Fedora-12 with a kernel built from 2.6.34-rc1-tip+ git tree running on Quad-Core AMD Opteron(tm) Processor 2350. Is there some combination of kernel/distribution/hardware that the hardware performance counters are suppose to work on?
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