Re: Spinlocks, yet again: analysis and proposed patches

"Min Xu (Hsu)" <xu@cs.wisc.edu> writes:
> ...If this were the case, perhaps first fetch the spin lock with read-only
> permission should have helped.

But the cmpb instruction in the 8.0 version of TAS would have done that,
and I think we've already established that the cmpb is a loss on most
machines (except maybe single-physical-CPU Xeons).  I suggested in my
other message that it might help to grab write permission on the cache
line before actually trying to acquire the spin lock --- but I don't see
how getting read-only permission first will help.
        regards, tom lane