On Mon, Nov 30, 2020 at 9:08 AM Tom Lane <t...@sss.pgh.pa.us> wrote: > Krunal Bauskar <krunalbaus...@gmail.com> writes: > > On Mon, 30 Nov 2020 at 10:14, Tom Lane <t...@sss.pgh.pa.us> wrote: > >> The results I posted at [1] seem to contradict this for Apple's new > >> machines. > > > For the results you saw on Mac-Mini was LSE enabled by default. > > Hmm, I don't know how to get Apple's clang to admit what its default > settings are ... anybody? > > However, it does accept "-march=armv8-a+lse", and that seems to > not be the default, because I get different results from my spinlock- > pounding test than I did yesterday. Abbreviating into a table: > > --- CFLAGS=-O2 --- --- CFLAGS="-O2 -march=armv8-a+lse" > --- > > TPS HEAD CAS patch HEAD CAS patch > > clients=1 2127 2174 2612 2722 > clients=2 1816 859 892 950 > clients=4 714 519 610 468 > clients=8 - - 108 185 > > Unfortunately, that still doesn't lead me to think that either LSE > or CAS are net wins on this hardware. It's quite clear that LSE > makes the uncontended case a good bit faster, but the contended case > is a lot worse, so is that really a tradeoff we want?
I tend to think that LSE is enabled by default in Apple's clang based on your previous message[1]. In order to dispel the doubts could you please provide assembly of SpinLockAcquire for following clang options. "-O2" "-O2 -march=armv8-a+lse" "-O2 -march=armv8-a" Thank you! Links 1. https://www.postgresql.org/message-id/663376.1606432828%40sss.pgh.pa.us ------ Regards, Alexander Korotkov
