[linux-audio-dev] Re: Low Latency patches and kernel 2.6.x

[Andrew Morton]

Florian Schmidt <mista.tapas at gmx.net> wrote:
>
> 
> Hi Andrew,
> 
> i'm a user of a 2.4.22 kernel patched with the preemption patches plus
> your Low Latency patches. It works very nicely for audio applications
> [like jackd, ardour, etc...].

Cool.

> Looking into the config menu of the 2.6.0 kernel i only find a
> "preemptible kernel" config option. Your low latency patches seem not to
> be included. Do you have plans of including your patches in the 2.6.x
> kernel? I heard rumors about merging the preemptible and your LL patches
> since they seem to go very nicely together.. Any truth to that?

The objective in 2.6 is that the preemptible kernel achieve similar
worst-case latencies to the low-latency-patched kernel.  So 2.6 should meet
your requirements out of the box.


That being said, last time I instrumented the 2.6 kernel it was not
achieving the targets.  The specific failure was occurring when the machine
had a very large number of inodes in cache and the VM system was reclaiming
those inodes.

It is unlikely that you will strike this problem in real-world usage, so
2.6 should work fine for you.  As ever, testing results would be
appreciated.

(The inode reclaim problem is fairly complex, but I just happen to see a
patch from Dipankar Sarma in my inbox this morning which is designed to fix
it up).