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SubjectRe: kflushd and/or update: Performance Killer?

On Mon, 19 Apr 1999 20:49:31 +0200, Helmut Metzdorf
<> said:

> first i noticed some weird events, such as waiting several seconds for
> characters typed to be echoed to the screen, extremly long load times
> for normally fast applications like vi, ls etc. and at least repeated
> error messages from fetchmail about timeouts (client server sync
> failiure).

From the description you've given here it's impossible to tell if your
system is slow because of scheduling or because of disk thrashing. What
does "vmstat 1" output look like when this occurs?

> top and/or free showed the amount of memory used for buff seemingly
> at the lowest possible values ...

> next i had a look at the processes shown by top and noticed a steep
> increase of usage by the processes kflushd and/or update. where i was
> used to see accumulated time on them of fractions of seconds during a
> whole day, now top showed 10 and more seconds runtime after one hour.

Those are perfectly normal. If the system has spent any significant
time with the caches busy you could easily accumulate much more time
than that in the update/flush daemons.

What is your self-written program actually doing in the background when
this happens, by the way?


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