Re: reading files in /proc/acpi hangs machine for a short time

[wwp <subscript-GANU6spQydw@public.gmane.org>]

Hello Michael,


On Fri, 25 Jun 2004 19:29:54 +0800 "Michael Frank" <mhf-jjFNsPSvq+iXDw4h08c5KA@public.gmane.org> wrote:

> On Fri, 25 Jun 2004 08:29:29 +0200, wwp <subscript-GANU6spQydw@public.gmane.org> wrote:
> 
> > Hi there,
> >
> > many acpi programs that show the battery/etc. usage that I tested are making
> > my system not to respond for a very short while, but periodically. For
> > instance, the mouse is being locked for 1/n of a second, which is not a big
> > loss of performance, but it really damn itchy for a normal (intensive) usage
> > of my Dell Inspiron 8200 laptop (kernel 2.4.26). I do remember of some
> > programs that were not producing such itchyness a long time ago (maybe
> > because the kernel things were different?).
> >
> > I've found that if I some files from /proc/acpi (let's say battery state), I
> > get the same behaviour.
> >
> > So my questions are:
> > - is this a known issue?
> > - program/kernel/dsdt/what-else issued?
> > - are there known workarounds?
> > - is it possible to get the acpi states from another place that /proc (if only it
> > doesn't show the same problem)?
> >
> 
> First figure out whether it is the PM app or ACPI.
> 
> 1) Disable all PM apps touching /proc/acpi.
> 
> 2) In a seperate terminal or VT run a script like
> 
> while :; do cat /proc/acpi/xxx/xxx/what_you_want_to_test > /dev/null; usleep 300000; done
> 
> Example sleeps 300ms (300000us) after every read, try various settings
>  from as low as 100ms to 10s and see how you system behaves.
> 
> If you don't have usleep sleep will do in 1s increments...
> 
> Note also can try cat /proc/acpi/battery/*/*
> 
> Run it continuously in the background and hopefully the test will show problems
> due to ACPI proc accesses. If not, the PM  apps are the problem - are these running
> big scripts or impose high system load somehow?

Thanks for your reply :-).

Excepted acpid 1.0.3, no (known) tool is playing with ACPI. When I run
wmpower/wmacpi or some other ACPI-aware PM tools, or if I do cat
/proc/acpi/battery/*/* by myself, then I can see the slowlyness (the period
depends on the wmpower refresh rate, or how often I do cat /proc/acpi/...).

Without any of these attempts (wmpower or cat /proc/acpi/...), my system
behaves normally. So it seems to me that accessing to files ini
/proc/acpi/bla/bla from C code or script behaves the same, it slows down the
machine for a very short while, because of CPU eating.


Regards,

-- 
wwp


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