Re: Some interesting results from tweaking spinlocks

> 2. In this example, almost one in ten LWLockAcquire calls results in
> blocking (calling IpcSemaphoreLock).  That seems like a lot.  I was
> seeing much better results on a uniprocessor under essentially the
> same test: one in a thousand LWLockAcquire calls blocked, not one in
> ten.  What's causing that discrepancy?
> 
> 3. The amount of spinlock-level contention seems too high too.  We
> are calling s_lock about one out of every hundred LWLockAcquire or
> LWLockRelease calls; the equivalent figure from a uniprocessor profile
> is one in five thousand.  Given the narrow window in which the spinlock
> is held, how can the contention rate be so high?
> 
> Anyone see an explanation for these last two observations?

Isn't there tons more lock contention on an SMP machine.  I don't see
the surprise.

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