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SubjectRe: kupdate, high CPU usage


Jeroen Geusebroek wrote:

> Hi there,
>
> Could someone explain what kupdate and kflushd do? I have a strange problem,
> when i ftp to my server, i get like 6500Kb/s for the first then seconds.
> That's
> the same speed i get to another server on the same subnet.
>
> But within a few seconds the CPS suddenly drops to 2500kb/s and when i look
> at the server i see that kupdate takes 80% of the cpu usage. I tried to
> disable kupdate ( i searched the mailinglist on how to do that ) kflushd
> had the same behaviour.
>
> Coould some explain what could be causing the trouble? I'm using the 2.2.16
> kernel.
>

As a non-kernel hacker I'd guess that after the seconds of full speed, your RAM
buffers are full and need to be flushed to disk, so you network speed drops to
disk speed. And the 80% usage may be due to the IO overhead of PIO or DMA. This,
of course, implies that you are actually downloading something to disk, but
because you say "ftp", it is likely that you do not ftp to /dev/null. You could
try that, maybe it's faster. :o)

>
> Thanks,
>
> Jeroen Geusebroek
>
> P.s. please reply to me directly or CC me, because i'm not on the list.

Xuân. :o)



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