Re: About “context-switching issue on Xeon” test case ？

Scott Marlowe wrote:
> For 2 sockets Intel rules the roost. I'd imagine AMD's much faster
> bus architecture for >2 sockets would make them the winner, but I
> haven't had a system like that to test, either Intel or AMD.
>

AMD has been getting such poor performance due to the RAM they've been
using (DDR2-800) that it really doesn't matter--Intel has been thrashing
them across the board continuously since the "Nehalem" processors became
available, which started in volume in 2009. Intel systems with 3
channels of DDR3-1066 or faster outperform any scale of AMD deployment
on DDR2, and nowadays even Intel's chapter desktop processors have 2
channels of DDR3-1600 in them.

That's been the situation for almost 18 months now anyway. AMD's new
"Magny-Cours" Opterons have finally adopted DDR3-1333, and closed the
main performance gap with Intel again. Recently I've found the "Oracle
Calling Circle" benchmarking numbers that Anand runs seem to match what
I see in terms CPU-bound PostgreSQL database workloads, and the latest
set at
http://it.anandtech.com/show/2978/amd-s-12-core-magny-cours-opteron-6174-vs-intel-s-6-core-xeon/8
show how the market now fits together. AMD had a clear lead when it was
Xeon E5450 vs. Opteron 2389, Intel pulled way ahead with the X5570 and
later processors. Only this month did the Opteron 6174 finally become
competitive again. They're back to being only a little slower at two
sockets, instead of not even close. A 4 socket version of the latest
Opterons with DDR3 might even unseat Intel on some workloads, it's at
least possible again.

Anyway, returning to "context switching on Xeon", there were some
specific issues with the older PostgreSQL code that conflicted badly
with the Xeons of the time, and the test case Tom put together was good
at inflicting the issue. There certainly are still potential ways to
have the current processors and database code run into context switching
issues. I wouldn't expect that particular test case would be the best
way to go looking for them though, which is the reason I highlighted its
age and general obsolescence.

--
Greg Smith 2ndQuadrant US Baltimore, MD
PostgreSQL Training, Services and Support
greg(at)2ndQuadrant(dot)com www.2ndQuadrant.us