On 08/02/2010 06:20 PM, Jeremy Fitzhardinge wrote: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
+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;
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.)
Hm. The tracing code already uses a specialized lock (arch_spinlock_t), perhaps we can make this lock avoid the tracing?
It's really sad, btw, there's all those nice lockless ring buffers and then a spinlock for ftrace_vbprintk(), instead of a per-cpu buffer.