Bug#509215: 'top' doesn't report multi-core CPU usage properly w/ default kernel
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.
Best,
Keith
-----Original Message-----
>From: Moritz Muehlenhoff <jmm@inutil.org>
>Sent: Dec 25, 2008 11:01 AM
>To: Keith Godfrey <aquilonis@earthlink.net>
>Cc: 509215@bugs.debian.org, jmm@debian.org, control@bugs.debian.org
>Subject: Re: 'top' doesn't report multi-core CPU usage properly w/ default kernel
>
>reassign 509215 linux-2.6
>thanks
>
>Keith Godfrey wrote:
>>
>> Hardware: Dell Optiplex
>> CPU: Core 2 quad
>> OS: Lenny - fresh install ~Dec 15th
>>
>> Testing configuration and report:
>> I have a pthreads based scientific application that uses ~170% and 250% CPU usage when running 2 and 3 threads, respectively. This behavior has been consistent on several systems, including MacOS and a previous version of Lenny. CPU usage was measured using 'top'.
>>
>> On the freshly installed Lenny, 'top' reported between 70%-105% usage for both 2 and 3 threads. The time required for the application to complete was comparable to runtimes on MacOS and a previous version of Lenny (all using the same or similar CPUs).
>>
>> I compiled a new kernel (2.6.27.10), basing it the config stored in /boot, incorporating minor additional changes. Under the newly compiled kernel, 'top' appears to report correct CPU usage. Application runtime remains the same.
>>
>> It apperas that 'top' is reporting incorrect CPU usage on the default kernel. It is also possible that the multi-threading doesn't speed anything up in this application (very possible) and that the default kernel wasn't properly handling the threads, whereas 'top' is OK.
>
>top parses /proc/stat, so it might either be that the data from it
>is inconsistent in the 2.6.26 kernel or that top fails to parse
>the output properly.
>
>Could you compare the content of /proc/stat from both kernels?
>
>Cheers,
> Moritz
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