Subject: Re: [linux-audio-dev] huge latency peaks with 2.4.10-smp kernel
From: Kai Vehmanen (kai.vehmanen_AT_wakkanet.fi)
Date: Fri Oct 19 2001 - 13:31:10 EEST
On Fri, 19 Oct 2001, Takashi Iwai wrote:
[preemptive kernel patch]
> However even PE patched kernel can cause unacceptably high latency.
> PE patch checks context switching with help of spinlock/unlock hacks.
> Thus it cannot overcome the long spinlock itself, which can be seen in
> VM and fs. Consequently PE patch requires also the LL'ish
> preemption/scheduling checks inside the long locked loops to reduce
> the high peaks.
And given that a) PE-patch "just" uses the existing SMP-lock points,
and b) I just reported +3000msec breaks running a SMP-kernel.
But of course, it's clear that if a piece of kernel code halts an
SMP-machine for that long, it's not just a low-latency issue anymore - the
code-path in question needs tuning.
-- http://www.eca.cx Audio software for Linux!
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