Subject: [linux-audio-dev] (not so low) low latency - acpi, dri, proc
From: Fernando Pablo Lopez-Lezcano (nando_AT_ccrma.Stanford.EDU)
Date: Wed Aug 21 2002 - 23:13:31 EEST
Hi... anybody out there testing latency on an ACPI patched
kernel? I have two kernels I'm testing:
2.4.19-x:
2.4.19
2.4.20-pre4
low latency for 2.4.19 (w/a couple of tweaks to patch pre4)
acpi-20020815 for 2.4.20-pre4
2.4.18-x:
2.4.18
low latency for 2.4.18-pre10
acpi-20020726 for 2.4.18
On both 2.4.18-x and 2.4.19-x I get quite high periodic
latency peaks that hover around 170mSecs.
I suspect acpi might be the culprit but I cannot try to
disable it because on this particular laptop you need acpi to
make sound work (probably something to do with routing of
interrupts,, also tried pci=biosirq on a non-acpi kernel
without success). Any suggestions?
DRI: I was about to write something about this and then
checked and yes, the latest lowlat patch (for 2.4.19) is
missing the dri reschedules (from Jussi Lako's patch set) so
that DRI is unusable if you don't add them (at least on a
Radeon based laptop). I'm recompiling with them to do more
tests.
Proc: something has changed from the 2.4.18 to the 2.4.19
kernels (maybe the acpi proc interface is to blame?). Big
mess of latency spikes in the proc latency test.
I'll post latency graphs later... this is all using
latencytest 0.42
-- Fernando
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