Re: APM killing low-latency performance on BX mainboard (we need a method to disable it dynamically)

Benno Senoner (sbenno@gardena.net)
Thu, 11 Nov 1999 01:11:54 +0100


On Thu, 11 Nov 1999, Michael K. Johnson wrote:
> Benno Senoner writes:
> >Now my question: in order to achieve best low-latency performance, we
> >need a way to disable APM on problematic boxes, but without recompiling
> >the kernel.
>
>

>
> We (Red Hat) did not include apm in our default kernels until there was
> a way to disable it on the kernel command line. Just use "apm=off".
> For what it's worth, a search for "apm" in our knowledgebase finds that
> information. Unfortunately, Documentation/kernel-parameters.txt does
> not list the possible values, so you couldn't have found it there.
> However, arch/i386/kernel/apm.c:apm_setup() is where the parsing is
> done.
>
> Hope that helps,
>
> michaelkjohnson
>

I'm happy that the "apm=off" option does exist:
This will allow that the user will always have a way to get
the best realtime performance out of Linux.
In future it would be nice to have GUI tools for dummies which
let you tune the performance of the kernel in order to suit your needs:

for example "tune for realtime performance"
turns APM off and turns on DMA / unmaskirq /32bit access
on all EIDE device.
It seems trivial but these settings really increase
the lowlatency performance by orders of magnitude.
( in the case of my DVD drive (untuned/tuned), the
latencies went down from 70ms to 2ms = 35times.
:-)

Benno.

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