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

Robert Watson rwatson at FreeBSD.org
Mon Dec 3 03:46:02 PST 2007

On Mon, 3 Dec 2007, Alexey Popov wrote:

> Mark Linimon wrote:
>>> I used 7.0-BETA3 and it is much worse.
>> Ouch.  A lot of systems see improvement.  Thanks for trying it out.  I hope 
>> that one of the people that has been doing the actual work can now comment 
>> (I am just an onlooker), and that you can be patient in the meantime. 
>> Unfortunately, Kris, who often looks at these kind of issues, is traveling 
>> for all of December and thus off the net.
> Is there any other FreeBSD developer who can take care of performance 
> problems on many-cores systems? Seems like upcoming 7-RELEASE and 
> 6.3-RELEASE would be completely unusable for us on that kind of systems i.e. 
> mostly on all modern hardware.

There are many FreeBSD developers who care a great deal about the performance 
of many-core systems.  However, it's also very late in the release cycle for 
7.0, and this sort of analysis requires a lot of time, so I don't think we 
will (or should) see any substantial changes at this point as they would 
require us to significantly extend the release cycle in order to test them 
properly.  The right path forwawrd at this point is to diagnosis the problems 
and work on fixing them in 8-CURRENT, and assuming they are not highly 
disruptive, MFC them for FreeBSD 7.1.

In general, the most important factor in optimizing performance is to get a 
good collaboration going between someone who can reproduce the problem, 
ideally in a way that can be shared with developers so they can also reproduce 
the problem, and provide testing and feedback over an extended period (several 
months) while the changes are developed and refined.  This is part of the role 
Kris has been playing with a number of FreeBSD developers -- Jeff, Attilio, 
myself, etc -- he set up highly reproduceable performance measurements and 
then worked with us to evaluate various patches to improve performance.  That 
kind of dynamic is invaluable, but it requires users who care a lot about 
performance (or whatever other factor it is) to spend a fair amount of time 
helping us.  Whether this is by providing a potted benchmark for developers to 
try out, or if this is by providing access to the test environment on their 
own systems, it's still critical.

I know from previous messages in the thread that you can't provide access to 
the actual application, but can you provide some sort of potted substitute 
that has similar performance properties -- be it php page sizes, database 
query load traces that can be replayed, etc?

Robert N M Watson
Computer Laboratory
University of Cambridge

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