Re: Spinlocks, yet again: analysis and proposed patches

Gavin Sherry <swm@linuxworld.com.au> writes:
> Interesting. On Xeon (2 phys, 4 log), with LWLock padded to 64 bytes and
> the cmpb/jump removed I get:
> [    1 55s    2 69s    4 128s ]
> This compares to the following, which is unpadded but has cmpb/jump
> removed but is otherwise vanilla:
> 1: 55: 2: 111: 4: 207

Hmm, that's pretty significant.  I tried it on a Xeon EM64T (thanks to
Stephen Frost for providing access), also 2 phys 4 log, and get:

Yesterday's CVS tip:1 32s    2 46s    4 88s    8 168s
plus no-cmpb and spindelay2:1 32s    2 48s    4 100s    8 177s
plus just-committed code to pad LWLock to 32:1 33s    2 50s    4 98s    8 179s
alter to pad to 64:1 33s    2 38s    4 108s    8 180s

I don't know what to make of the 2-process time going down while
4-process goes up; that seems just weird.  But both numbers are
repeatable.
        regards, tom lane