Re: [PATCH RFC 3/4] Paravirtualized spinlock implementation for KVM guests

[Jeremy Fitzhardinge <jeremy@goop.org>]

  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