Re: 20% performance drop on PostgreSQL 9.2 from kernel 3.5.3 to 3.6-rc5 on AMD chipsets - bisected

Borislav Petkov
2012-09-15T10:44:57Z

On Sat, Sep 15, 2012 at 06:11:02AM +0200, Mike Galbraith wrote:
> My wild (and only) theory is that this is userspace spinlock related.
> If so, starting the server and benchmark SCHED_BATCH should not only
> kill the regression, but likely improve throughput as well.

FWIW,

I went and tried it. Here are the exact steps:

$ ps ax | grep postgres
2066 ? S 0:01 /usr/lib/postgresql/9.1/bin/postgres -D /var/lib/postgresql/9.1/main -c config_file=/etc/postgresql/9.1/main/postgresql.conf
2070 ? Ss 0:07 postgres: writer process
2071 ? Ss 0:05 postgres: wal writer process
2072 ? Ss 0:01 postgres: autovacuum launcher process
2073 ? Ss 0:01 postgres: stats collector process
5788 pts/0 S+ 0:00 grep postgres

# set to SCHED_BATCH
$ schedtool -B 2066 2070 2071 2072 2073

# verify:
$ schedtool 2066 2070 2071 2072 2073
PID 2066: PRIO 0, POLICY B: SCHED_BATCH , NICE 0, AFFINITY 0x3f
PID 2070: PRIO 0, POLICY B: SCHED_BATCH , NICE 0, AFFINITY 0x3f
PID 2071: PRIO 0, POLICY B: SCHED_BATCH , NICE 0, AFFINITY 0x3f
PID 2072: PRIO 0, POLICY B: SCHED_BATCH , NICE 0, AFFINITY 0x3f
PID 2073: PRIO 0, POLICY B: SCHED_BATCH , NICE 0, AFFINITY 0x3f

$ su - postgres
postgres@hhost:~$ export PATH=$PATH:/usr/lib/postgresql/9.1/bin/
postgres@hhost:~$ schedtool -B -e pgbench -i pgbench && pgbench -c 10 -t 10000 pgbench

...

tps = 4388.118940 (including connections establishing)
tps = 4391.771875 (excluding connections establishing)

=> even better than the results with 3.5 (had something around 3900ish
on that particular configuration).

HTH.

--
Regards/Gruss,
Boris.