Hi Moritz,
I'd like to re-open this bug as I've again been successful at reproducing it.
I'm not sure if it's a 'top' problem, as originally reported, or something
deeper and performance related. The multi-threaded program I use as a benchmark
took 17.5 hours to complete and showed an average CPU load of 85% on the
default kernel (despite using 2 threads; machine 'Prevost' below). Running the
same program on a very similar machine ('Pender') took 12.5 hours and showed
~190% CPU load. Prevost had similar or faster performance than Pender before
the new Lenny install.
Please advise if/how I can help, and how to re-open the bug.
Many thanks and best regards,
Keith
-----Original Message-----
>From: Keith Godfrey <[email protected]>
>Sent: Dec 31, 2008 11:34 AM
>To: Moritz Muehlenhoff <[email protected]>
>Subject: Re: 'top' doesn't report multi-core CPU usage properly w/ default
>kernel
>
>Hi Moritz,
>
>I've managed to reproduce the problem, and the strange behavior is not
>restricted to the default kernel - I also observe odd behavior with a new
>kernel I've compiled, although not to the same extent. I've ran the same
>program on 3 different machines, all running Lenny, and the machine with a
>fresh Lenny install (~Dec 15th) performs notably worse than the other two.
>
>Machines:
> Pender: Dell Optiplex 745, Core 2 duo
> Prevost: Dell Optiplex 755, Core 2 quad, fresh install ~Dec 15th, the
> problem child
> Talisman: Pentium D duo, make unknown (cluster machine)
>
>As of Dec 30th: I have configured a scientific application to use 2 threads on
>each machine and to process the same set of data. The Core 2 duo and Pentium D
>duo each show ~190% CPU usage, while the Core 2 quad shows ~145%. The core 2
>quad is running on a recompiled kernel. The Core 2 duo and Core 2 quad have
>similar clock speeds, so the application should run similarly on both.
>However, consistent with the CPU usage stats, the Core 2 quad runs the
>application at only 75% of the speed of the Core 2 duo (again, both running 2
>threads).
>
>As of Dec 31st: After noting these problems, I rebooted into the original
>kernel and reran the same application. The application running w/ 2 threads
>uses ~80% CPU, according to top. I'm doing a speed trial presently, but won't
>have results until Jan 1st (it's a big and slow simulation...)
>
>Before the latest Lenny install, the Core 2 quad performed similarly
>(sometimes faster) than the Core 2 duo, so I don't think it's a hardware
>issue. It's possible that the install was bad...? The application has a huge
>RAM footprint and uses a lot of mutex synchronization, so, in general,
>application performance appears to be constrained by either bus throughput or
>synchronization issues. I've thought that it is possible that the new kernel
>reports CPU usage more accurately than previous iterations (i.e. better
>measuring of wait states), but the performance problems don't seem to support
>this hypothesis.
>
>I've attached /proc/stat data from all 3 machines (specifically: cat
>/proc/stat > stats.machine; uname -a >> stats.machine).
>
>Please let me know if there's any additional information I can provide (or
>additional tests).
>
>Many thanks,
>Keith
>
>
>-----Original Message-----
>>From: Moritz Muehlenhoff <[email protected]>
>>Sent: Dec 26, 2008 4:54 PM
>>To: Keith Godfrey <[email protected]>
>>Cc: [email protected]
>>Subject: Re: 'top' doesn't report multi-core CPU usage properly w/ default
>>kernel
>>
>>Keith Godfrey wrote:
>>> I am no longer able to reproduce this bug. Please close it and I will
>>> assume that I was somehow doing something wrong (or the computer simply
>>> needed a reboot). If I am able to reproduce it again, I shall contact you.
>>>
>>> Sorry about the apparent false alarm.
>>
>>Thanks, closing the bug then.
>>
>>Cheers,
>> Moritz
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