2 x quad-core system is slower that 2 x dual core on FreeBSD
kris at FreeBSD.org
Thu Nov 29 11:27:34 PST 2007
Alexey Popov wrote:
> 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
>>>> 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.
> I didn't measured the exact values of requests per second on ULE with
> patch and without patch, but at first glance the benefits of the patch
> are similiar to 4BSD. If you need this values, I'll obtain them.
> Here you can find lock profiling results for 7-BETA3 GENERIC kernel with
> SCHED_ULE running optimized PHP and unoptimized, with your patch and
> without it: http://22.214.171.124/gprof/lockmgr/
> This data was collected by th following script:
> (sysctl debug.lock.prof.reset=1
> sysctl debug.lock.prof.enable=1
> sleep 60
> sysctl debug.lock.prof.enable=0
> sysctl debug.lock.prof.stats
> top -d 2 -b | tail -25)
> AFAIU there's still high contention on "lockbuilder mtxpool" with patch
> applied. But hopefully "lockmgr:ufs" contention which i believe produced
> 80%sysCPU load is gone with your patch.
Looks to me like lockmgr-related contention was reduced by 1 to 2 orders
of magnitude, which is the expected result. This surely must have a
measurable impact on your workload. Further lockmgr improvement will
have to wait until the lockmgr replacement work proceeds.
One more patch which may or may not help is:
(may also require porting since it was against an older version of
7.0-CURRENT). When I have tested this in the past it was a performance
loss for reasons that I think I understand (basically, it is locally a
performance improvement for the name cache but also requires a fixed
lockmgr to avoid an overall performance loss), but I don't remember if I
tested it in conjunction with the lockmgr patch.
>> 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
> I think it would be very useful because I can't see any other ways to
> profile FreeBSD on the modern many-cores machines.
You can extract the changeset from my branch via
http://perforce.freebsd.org. Unfortunately I don't have time to do it
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