Re: [linux-audio-user] Latency issues with laptops

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Subject: Re: [linux-audio-user] Latency issues with laptops
From: Rui Nuno Capela (rncbc_AT_rncbc.org)
Date: Tue Oct 12 2004 - 02:51:20 EEST


Lee Revell wrote:
> One of the JACK developers reported this problem on LKML and the reply
> was very interesting, this could explain a lot of the weird latency
> issues that laptop users are seeing.
>
> http://lkml.org/lkml/2004/10/11/182
>
> The basic issue seems to be if your laptop has a broken BIOS which
> implements ACPI using SMM you are out of luck. Here is some more
> information on the problem (near the end of the page):
>
> http://www.infoworld.com/cgi-bin/displayNew.pl?/glass/bg112596.htm
>
> If ACPI causes you massive xrun/latency problems then you might have
> such a broken BIOS. If you are having weird latency problems with a
> laptop, even with ACPI disabled, try to see if it corresponds to the fan
> turning on or changing speed. If so then you might be screwed :-(
>
> There does not seem to be a lot of hope if you do have one of these
> broken machines. But we can at least identify the problematic laptops,
> complain to the manufacturers, and warn people not to buy them.
>

My laptop, a Compaq Presario 2516EA, probably suffers from this ACPI disease.

However, this has been mitigated by just disabling it; just booting with
acpi=off the xrun rate is almost negligible (e.g.running 2.6.9-rc3-mm3-T3
UP).

Don't know if the SMM issue is deadly hidden and commanded somewhere from
BIOS, then making life a pain, even though apci is off. How can I check
this?

For the record, I'm quite used for acpi being a real pita, but the lack of
it doesn't seem to be much important to me. OK, with acpi=off, I miss
battery status, temparature monitoring, whatever, just to name a few
goodies, but I buy that for cheap, just about when I get to do low-latency
audio.

For example, I can do along with jackd -p128 -n2 using the onboard audio
(ali5451) without much trouble, iif acpi=off, otherwise a xrun breakbeat
is featured ;)

Take care.

-- 
rncbc aka Rui Nuno Capela
rncbc_AT_rncbc.org


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