We are pleased to announce the next update to our new preempt-rt
series.
- port forward to 2.6.29-rc8
- disable -rt conflicting config options
- hotplug cpu fixes (peterz)
- slab/pagealloc lock breaks (peterz / tglx)
- sigqueue caching for -rt tasks
- posixtimer thread avoid useless wakeups
- various build fixes (mingo, frank ....)
- lots of tracer updates from -tip (check the tip git logs)
The outstanding improvement is the slab/pagealloc change which breaks
and splits locking and brought down worst case latencies in
problematic use cases from >500us to <100us.
As a side note:
There seems to be a wide spread underestimation of the problem spots
exposed by preempt-rt. The usual shrug off answer is:
"I don't care about -rt. Come back if you can expose the same
problem in the mainline kernel."
This is a fundamentally wrong answer.
preempt-rt mostly exposes existing latency spots and magnifies
them
Reducing latencies in -rt by a factor 5 will be not that
prominent in a non-rt setup, but the problematic code area
will still produce measureable latency problems.
I'm well aware of the tradeoff between determinitic behaviour and
throughput, but problematic spots (e.g. lock contentions) hurt
both.
So can we please put down the stupid "I don't care about -rt"
attitudes and accept that we have to think about the mutual
benefits of deterministic and throughput aspects without hurting
each other ?
Download locations:
http://rt.et.redhat.com/download/
http://www.kernel.org/pub/linux/kernel/projects/rt/
Information on the RT patch can be found at:
http://rt.wiki.kernel.org/index.php/Main_Page
to build the 2.6.29-rc8-rt1 tree, the following patches should be
applied:
http://www.kernel.org/pub/linux/kernel/v2.6/testing/linux-2.6.29-rc8.tar.bz2
http://www.kernel.org/pub/linux/kernel/projects/rt/patch-2.6.29-rc8-rt1.bz2
The broken out patches are also available at the same download
locations.
Enjoy !
tglx
P.S.: ARM/PowerPC support is in the pipeline and will be available
with -rt2 (hopefully :)
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