On Mon, Jan 18, 2016 at 3:04 PM, Andres Freund <and...@anarazel.de> wrote: > On January 18, 2016 7:27:59 PM GMT+01:00, Robert Haas <robertmh...@gmail.com> > wrote: >> On Sun, Jan 17, 2016 at 6:38 AM, Andreas Seltenreich <seltenre...@gmx.de> >> wrote:
>>> While discussing issues with its developers, it was pointed out to me >>> that our spinlock inline assembly is less than optimal. Attached is >>> a patch that addresses this. >> I did a Google search and everybody seems to agree that the LOCK >> prefix is redundant. I found a source agreeing with the idea that it >> doesn't clobber registers >> So I guess it would be safe to change this. Scares me slightly, >> though. > > Clobbers IIRC are implicit on x86 anyway. Rather doubt that the > space for the prefix makes any sorry of practical difference, but > there indeed seems no reason to have it. I took a look at this and agree that the shorter, simpler code proposed in this patch should make no *logical* difference, and looks like it *should* have a neutral or beneficial affect; but performance tuning in general, and spinlock performance in particular, is full of surprises. We have seen customers suffer poor scaling on their brand new monster machines because of the interaction between NUMA scheduling and our spinlock implementation, and seen those problems go away with an upgrade from pre-3.8 to post-3.8 kernels. I would be hesitant to accept this change without seeing a benchmark on a large NUMA machine with 4 or more memory nodes, on Linux kernels both before and after 3.8, to make sure that the effects are at least neutral. -- Kevin Grittner EDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
