2 x quad-core system is slower that 2 x dual core on FreeBSD

[Antony Mawer]

On 3/12/2007 8:50 PM, Alexey Popov wrote:
> Hi
> 
> Alexey Popov wrote:
>> Now we also have terribly performing PostgreSQL on 8-core server. We 
>> noticed the slowdown after moving PostgreSQL from 2xXeon 3.0 
>> Apache+PostgreSQL server to dedicated PostgreSQL server. I collected 
>> some stats (see attach) before moving to Linux.
> Sorry for the broken top ouptut in previuos message. Here's the correct 
> one.
> 
> last pid: 70857;  load averages: 35.05, 37.11, 33 up 25+23:08:00  12:46:29
> 94 processes:  46 running, 48 sleeping
> CPU: 17.0% user,  0.0% nice, 80.5% system,  0.2% interrupt,  2.3% idle
> Mem: 1209M Active, 1890M Inact, 494M Wired, 143M Cache, 214M Buf, 127M Free
> Swap: 2048M Total, 72K Used, 2048M Free

Have you tried testing with different values for kern.hz? I am by no 
means an expert, but have stumbled across various postings over the past 
few years that suggest the high value (1000) used by modern (5.x+?) 
kernels can be pessimistic for some workloads...

If you could try testing with some other values by setting in 
/boot/loader.conf, eg:

     kern.hz="100"

Perhaps testing 100 and 200 to see how they fare against the default 
value of 1000, would at least provide some indicator as to whether this 
has any bearing on performance.

Some with a better knowledge of the kernel internals may be able to 
support or dimiss this idea, but as Kris is off on holidays I figured 
any suggestion was worthwhile! ;-)

I'd also like to say thanks for your efforts to help test and track down 
the cause of these performance problems - in the end the whole community 
benefits, so the more you are able to test and help resolve these things 
the better for us all... :-)

--Antony