performance degradation in 6.2 when adding a second quad core chip

benjamin thielsen bthielsen at
Fri Feb 22 14:35:52 UTC 2008

On Feb 21, 2008, at 17.49, Kris Kennaway wrote:

> benjamin thielsen wrote:
>> hi folks-
>> we've been experiencing some interesting behavior on single quad  
>> core computers as compared to dual quad core computers.
> Yes, this can happen when you run into concurrency bottlenecks in  
> the application or in the kernel.
>> it appears that adding a second processor to the system (leaving it  
>> otherwise untouched) actually decreases performance.  we've got a  
>> small rudimentary test process, built in house, that does  
>> postgresql queries (selects) via http requests (apache2/php5).
> 7.0 will perform much better than 6.x on SMP workloads in general,  
> however TCP I/O is not yet at the point where it can make efficient  
> use of many processors (there has been a lot of work on TCP in 7.0,  
> but it is not yet at the stage where a performance payoff will be  
> seen with more than about 4 CPUs).  This is one of the projects that  
> we will be working on this year, so you can expect future releases  
> to have improved concurrent TCP performance.
> There may be other issues, so if you like you can enable  
> LOCK_PROFILING and obtain a trace when your workload is running (see  
> the manpage).  You should also try the ULE scheduler on 7.0.

i apologize - i neglected to mention that we are using ule on 7.0.

what do you guys generally endorse/recommend for local(non-network)  
load/performance testing?


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