[linux-audio-user] 2.6.13 kernel: which patches for better latency

Eric Dantan Rzewnicki rzewnickie at rfa.org
Mon Sep 12 15:06:14 EDT 2005


On Thu, Sep 08, 2005 at 08:38:02PM -0500, Reuben Martin wrote:
> On 9/7/05, guy <sayhi2guy at tiscali.co.uk> wrote:
> > Hi
> > I'm just about to compile a 2.6.13 kernel for low latency audio work.
> > The docs I have accessed are either confusing (sorry if its just me ;0)
> > ) or rendered out of date by kernel developments.
> > I know that some features such as pre-empt are now in the kernel.  Which
> > patches (if any) would you folks advise that I should apply.  I am also
> > unsure if should enable the 'big kernel lock' feature.
> > Thanks in advance for any help
> realtime-preempt patches are the latest and greatest for latency
> improvements. They are very actively maintained by Ingo Molnar, same
> guy who created the preempt patches for the 2.4 kernel series.

For historical clarification ( and someone correct me if I'm wrong on
any of this ), Ingo did a set of low latency patches for 2.2/2.4 that
basically showed that breaking up long code pathes could improve linux's
latency performance. These were proof of concept patches, in a sense,
but not accepted, nor intended, for the mainline kernel.

Andrew Morton created a smaller and more tightly focused set of
long-code-path-splitting low-latency patches for 2.4 inspired by Ingo's
earlier work. These were intended to find an approach to achieving
low-latency more acceptable to the kernel devs.

Robert Love created a set of Preemption patches for 2.4 that were
commonly applied along with Andrew's LL patches. The preemption patches
were a different approach to achieve low-latency which allowed code
paths which might run for a long time to be marked as pre-emptible.

Much of Andrew and Robert's work on 2.4 was incorporated into the 2.5
development kernel and thus the 2.6 series. However there were still
latency problems with 2.6, so Ingo has again taken the lead in producing
the current series of realtime-preemption patches. A lot of this work is
now present in the mainline 2.6.13.x kernel.

> http://people.redhat.com/mingo/realtime-preempt/
> 
> This patch removes "big kernel lock" option. (You don't want it and
> the patch at the same time)
> 
> The patch is updated every couple of days.
> 
> Good luck.
> -Reuben

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