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 starved by it. Since I cared about determinism more than performance, I killed it. But Gregory brought it back for SCHED_OTHER tasks. - rtmutex rearrange logic (Gregory Haskins) This patch isn't that great of performance, but sets up for adaptive spinlocks, as well as removes an extra xchg (but adds one, see next patch) - rtmutex remove double xchg (Steven Rostedt) This patch removes a double xchg that happens on getting the rt_mutex. as well as getting rid of the unneeded update_current. No real performance benefits here. [root@bxrhel51 c]# cat hack-test-2.6.24.7-rt6-02-rearrange-xchg Time: 7.741 Time: 8.007 Time: 8.061 Time: 8.080 Time: 8.105 Time: 8.223 Time: 8.207 Time: 8.220 Time: 8.230 Time: 8.214 - adaptive spinlocks (Gregory Haskins, Sven Deitrich, Peter Morreale, and Steven Rostedt) I played a bit with different ways to do the adaptive spinlocks, but found that guaranteeing that the highest prio task is a pain, and that I needed to go into the slow path to handle this. Well, the guys at Novell pretty much did that. But unfortunately, they did all sorts of funny things (adding unneeded structures, adding stuff to task_struct, and grabbing tasks in inappropriate places). Since I spent quite a bit of time trying to do this, I had a good idea of what was needed, so I rewrote their patch to what it should have been to begin with. Don't get me wrong, getting this to work was solely at the hands of the Novell guys. I just had to clean it up a bit. Here's the result: [root@bxrhel51 c]# cat hack-test-2.6.24.7-rt6-03-adaptive-locks Time: 4.752 Time: 4.830 Time: 4.896 Time: 4.858 Time: 4.801 Time: 4.885 Time: 4.794 Time: 4.883 Time: 4.852 Time: 4.911 to build a 2.6.24.7-rt7 tree, the following patches should be applied: http://www.kernel.org/pub/linux/kernel/v2.6/linux-2.6.24.tar.bz2 http://kernel.org/pub/linux/kernel/v2.6/patch-2.6.24.7.bz2 http://rt.et.redhat.com/download/patch-2.6.24.7-rt7.bz2 ***** NOTE ****** These patches have already been ported to 2.6.25-rt. But that kernel is still going through some needed testing. ***** NOTE ***** And like always, my RT version of Matt Mackall's ketchup will get this for you nicely: http://people.redhat.com/srostedt/rt/tools/ketchup-0.9.8-rt3 The broken out patches are also available. -- Steve -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
