CentOS - PostgreSQL 9.2.13 -> 9.4

Hi,

I've been tuning our new database server, here's some info...

CentOS Linux release 7.1.1503 (Core)
3.10.0-229.11.1.el7.x86_64

8 x 16GB 1600MHz PC3-12800 DDR3 - 128GB total
2 x AMD Opteron 6386SE 2.8GHz/16-core/140w - 32 cores total
4 x 300GB SAS 10k HDD - raid 1+0 configuration
1GB FBWC for P-series smart array - cache enabled

I'm using the CentOS provided packages for PostgreSQL
Version : 9.2.13
Release : 1.el7_1

I'm getting fairly good statistics from this server but after asking for
some advice I was pointed towards PostgreSQL 9.3 (posix memory
management) and PostgreSQL 9.4 (pg_replication_slots).

I dropped my original install of 9.2.13 above and went straight to the
9.4 from the PostgreSQL repositories.

Are there any known issues with my kernel and PostgreSQL? I found this
post -
http://www.databasesoup.com/2014/09/why-you-need-to-avoid-linux-kernel-32.html

which states there are known issues up to kernel 3.10.. the reason I
ask, no matter how small or big a configuration change I make I can't
match my 9.2.13 install. I'm seeing huge decreases in TPS on all my
benchmarks.

for example, 9.2.13, my own extremely heavy SQL file being used here,
hence the lower TPS...

32 37.357197
64 34.145088
128 19.682544
256 9.910772
512 5.803358

compared to 9.4 - exactly the same tests and parameters configured (I
also started from defaults and tuned up as best I could).

32 14.982111
64 14.894859
128 14.277631
256 13.679516
512 13.679516

I'm now moving back to 9.2.13, deadlines are creeping closer by the day
and I just don't have time to figure this out.

I praised 9.4 for the new features and now I'm cursing it!

any info would be appreciated,

thanks

Michael