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SubjectRe: [PATCH RFC 3/4] Paravirtualized spinlock implementation for KVM guests
  On 08/02/2010 01:48 AM, Avi Kivity wrote:
> On 07/26/2010 09:15 AM, Srivatsa Vaddagiri wrote:
>> Paravirtual spinlock implementation for KVM guests, based heavily on
>> Xen guest's
>> spinlock implementation.
>>
>>
>> +
>> +static struct spinlock_stats
>> +{
>> + u64 taken;
>> + u32 taken_slow;
>> +
>> + u64 released;
>> +
>> +#define HISTO_BUCKETS 30
>> + u32 histo_spin_total[HISTO_BUCKETS+1];
>> + u32 histo_spin_spinning[HISTO_BUCKETS+1];
>> + u32 histo_spin_blocked[HISTO_BUCKETS+1];
>> +
>> + u64 time_total;
>> + u64 time_spinning;
>> + u64 time_blocked;
>> +} spinlock_stats;
>
> Could these be replaced by tracepoints when starting to spin/stopping
> spinning etc? Then userspace can reconstruct the histogram as well as
> see which locks are involved and what call paths.

Unfortunately not; the tracing code uses spinlocks.

(TBH I haven't actually tried, but I did give the code an eyeball to
this end.)

J



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