Re: HT on or off for E5-26xx ?

Well, the results are in and at least in this particular case
conventional wisdom is overturned. Not a huge benefit, but throughput is
definitely higher with HT enabled and nthreads >> ncores:

HT off :

bash-4.1$ /usr/pgsql-9.2/bin/pgbench -T 600 -j 48 -c 48
starting vacuum...end.
transaction type: TPC-B (sort of)
scaling factor: 100
query mode: simple
number of clients: 48
number of threads: 48
duration: 600 s
number of transactions actually processed: 2435711
tps = 4058.667332 (including connections establishing)
tps = 4058.796309 (excluding connections establishing)

avg-cpu:  %user   %nice %system %iowait  %steal   %idle
           52.50    0.00   14.79    5.07    0.00   27.64

Device:         rrqm/s   wrqm/s     r/s     w/s    rMB/s    wMB/s
avgrq-sz avgqu-sz   await  svctm  %util
sda               0.00  5700.30    0.10 13843.50     0.00 74.78
11.06    48.46    3.50   0.05  65.21

HT on:

bash-4.1$ /usr/pgsql-9.2/bin/pgbench -T 600 -j 48 -c 48
starting vacuum...end.
transaction type: TPC-B (sort of)
scaling factor: 100
query mode: simple
number of clients: 48
number of threads: 48
duration: 600 s
number of transactions actually processed: 2832463
tps = 4720.668984 (including connections establishing)
tps = 4720.750477 (excluding connections establishing)

avg-cpu:  %user   %nice %system %iowait  %steal   %idle
           40.61    0.00   12.71    3.09    0.00   43.59

Device:         rrqm/s   wrqm/s     r/s     w/s    rMB/s    wMB/s
avgrq-sz avgqu-sz   await  svctm  %util
sda               0.00  6197.10   14.80 16389.50     0.14 86.53
10.82    54.11    3.30   0.05  82.35

System details:

E5-2620 (6 core + HT 15Mb LL) 64G (4 channels with 16G 1333 modules),
Intel 710 300G (which is faster than the smaller drives, note),
Supermicro X9SRi-F Motherboard.
CentOS 6.3 64-bit, PG 9.2.1 from the PGDG RPM repository. pgbench
running locally on the server.