Re: KVM PMU virtualization

Peter Zijlstra
2010-03-02T09:57:05Z

On Tue, 2010-03-02 at 15:09 +0800, Zhang, Yanmin wrote:
> With vanilla host kernel, perf top data is stable and spinlock doesn't take too much cpu time.
> With guest os, __ticket_spin_lock consumes 28% cpu time, and sometimes it fluctuates between 9%~28%.
>
> Another interesting finding is aim7. If I start aim7 on tmpfs testing in guest os with 1GB memory,
> the login hangs and cpu is busy. With the new patch, I could check what happens in guest os, where
> spinlock is busy and kernel is shrinking memory mostly from slab.

Hehe, you've just discovered the reason for paravirt spinlocks ;-)

But neat stuff, although I don't think you need PERF_SAMPLE_KVM, it
should simply always report the guest sample if it came from the guest,
you can extend PERF_RECORD_MISC_CPUMODE_MASK to add guest states.