Re: Excessive context switching on SMP Xeons

Alan Stange wrote:

> Here's a few numbers from the Opteron 250. If I get some time I'll
> post a more comprehensive comparison including some other systems.
>
> The system is a Sun v20z. Dual Opteron 250, 2.4Ghz, Linux 2.6, 8 GB
> memory. I did a compile and install of pg 8.0 beta 3. I created a
> data base on a tmpfs file system and ran pgbench. Everything was "out
> of the box", meaning I did not tweak any config files.
>
> I used this for pgbench:
> $ pgbench -i -s 32
>
> and this for pgbench invocations:
> $ pgbench -s 32 -c 1 -t 10000 -v
>
>
> clients tps 1 1290 2
> 1780 4 1760 8 1680
> 16 1376 32 904

The same test on a Dell PowerEdge 1750, Dual Xeon 3.2 GHz, 512k cache,
HT on, Linux 2.4.21-20.ELsmp (RHEL 3), 4GB memory, pg 7.4.5:

$ pgbench -i -s 32 pgbench
$ pgbench -s 32 -c 1 -t 10000 -v

clients tps avg CS/sec
------- ----- ----------
1 601 48,000
2 889 77,000
4 1006 80,000
8 985 59,000
16 966 47,000
32 913 46,000

Far less performance that the Dual Opterons with a low number of
clients, but the gap narrows as the number of clients goes up. Anyone
smarter than me care to explain?

Anyone have a 4-way Opteron to run the same benchmark on?

-Bill

> How are these results useful? In some sense, this is a speed of light
> number for the Opteron 250. You'll never go faster on this system
> with a real storage subsystem involved instead of a tmpfs file
> system. It's also a set of numbers that anyone else can reproduce as
> we don't have to deal with any differences in file systems, disk
> subsystems, networking, etc. Finally, it's a set of results that
> anyone else can compute on Xeon's or other systems and make a simple
> (and naive) comparisons.
>
>
> Just to stay on topic: vmstat reported about 30K cs / second while
> this was running the 1 and 2 client cases.
>
> -- Alan