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

Kris Kennaway kris at FreeBSD.org
Fri Nov 23 02:57:30 PST 2007

Alexey Popov wrote:
> Hi.
> Kris Kennaway wrote:
>>> Now FreeBSD 7-STABLE ULE 8-core server without optimized PHP 
>>> realpath_cache_size (producing 2000+ lstats per request) can handle 
>>> up to ~24 rps as opposed to  max. 17 rps without your patch. %sys 
>>> never grows over %user with your patch. On the server with optimized 
>>> realpath_cache_size there's no visible influence of your patch.
>> You said "20" before for this configuration, so I'm a bit suspicious 
>> about how seriously to treat your measurements :)
> Sorry, my mistake. s/ULE/4BSD.

OK, please compare ULE to ULE with and without my patch (and remembering 
to enable the sysctl), and obtain lock profiling traces in both cases 
under identical workloads & durations.  That is what I need to proceed 
with this issue.

>> Anyway, please obtain another lock profiling trace using the same 
>> conditions as the previous one (same workload & duration, etc), so we 
>> can compare what changed.
> OK, I'll make it a little bit later.
> Also I tried to find what else is slow in FreeBSD, I tried hwpmc as 
> module and in kernel, but it fails with error:
> pmc: Unknown Intel CPU.
> module_register_init: MOD_LOAD (hwpmc, 0xffffffff804833e0, 
> 0xffffffff809338a0) error 78

There are patches you need to enable it on woodcrest.  They are in my p4 
branch (kris-contention) but I don't have time right now to extract them.

> This is related to 
> http://www.freebsd.org/cgi/query-pr.cgi?pr=amd64%2F111994&cat=
> and it is impossible to use hwpmc with modern CPUs.

Sounds like it.

> Is kgmon profiling usable on FreeBSD 7?

I've never bothered, it is likely to be quite slow, so it can totally 
change the workload you are trying to profile.


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