We are pleased to announce the 2.6.24.7-rt7 tree, which can be
downloaded from the location:
http://rt.et.redhat.com/download/
Information on the RT patch can be found at:
http://rt.wiki.kernel.org/index.php/Main_Page
Changes since 2.6.24.7-rt6
**** HUGE PERFORMANCE IMPROVEMENT!!! ****
This is the largest performance improvement to hit the RT patch
since the removal of the global PI lock. On my 4way box
running "hackbench 50" went from 18 seconds down to just under
5 seconds (4.8). Vanilla 2.6.24.7 on this same box runs at 3.9 secs.
This is the first time that the RT patched kernel is less than
a magnitude away from mainline running this hackbench test.
Here's a run of 10 "hackbench 50" on 2.6.24.7-rt6:
[root@bxrhel51 c]# cat hack-test-2.6.24.7-rt6-00-vanilla
Time: 16.651
Time: 16.773
Time: 16.500
Time: 17.437
Time: 16.267
Time: 18.296
Time: 16.524
Time: 17.452
Time: 18.595
Time: 18.357
The following patches are the reason for this great improvement!
- lateral lock stealing (Gregory Haskins)
[root@bxrhel51 c]# cat hack-test-2.6.24.7-rt6-01-lateral-steal
Time: 7.853
Time: 8.219
Time: 7.967
Time: 8.118
Time: 8.195
Time: 8.349
Time: 8.122
Time: 8.146
Time: 8.197
Time: 8.026
This alone brought the times down by almost 60% All this patch was to
do is allow an equal prio task (non-rt) to steal a lock from a pending
owner. This is very much similar to the problem that was recently
discovered with generic semaphores. They forced strict fairness, but
that hurts performance. We only do this with non-rt tasks, because RT
tasks need to be fair otherwise we risk a task being starved, and
even though its being starved by an equal prio RT task, I would not
want to explain that to my customers when they have two high prio
tasks bound to separate CPUS and one is starving the other.
When I first wrote the code to steal lock ownership, I originally had
lateral stealing, but notice that RT tasks were being st...
