On Tue, 2007-02-27 at 09:33 +0100, Ingo Molnar wrote:

* Michal Piotrowski [off-list ref] wrote:

quoted

Thomas Gleixner napisał(a):

quoted

Adrian,

On Mon, 2007-02-26 at 23:05 +0100, Adrian Bunk wrote:

quoted

Subject    : kernel BUG at kernel/time/tick-sched.c:168  (CONFIG_NO_HZ)
References : http://lkml.org/lkml/2007/2/16/346
Submitter  : Michal Piotrowski [off-list ref]
Handled-By : Thomas Gleixner [off-list ref]
Status     : problem is being debugged

The BUG_ON() was replaced by a warning printk(). The BUG_ON() exposed a
problem with the SMT scheduler. See below.

quoted

Subject    : BUG: soft lockup detected on CPU#0
             NOHZ: local_softirq_pending 20  (SMT scheduler)
References : http://lkml.org/lkml/2007/2/20/257
Submitter  : Michal Piotrowski [off-list ref]
Handled-By : Thomas Gleixner [off-list ref]
             Ingo Molnar [off-list ref]
Status     : problem is being debugged

Patch available, not confirmed yet.

I can confirm that the bug is fixed (over 20 hours of testing should 
be enough).

thanks alot! I think this thing was a long-term performance/latency 
regression in HT scheduling as well.

Agreed.

I was recently looking at that spot because I found that niced tasks
were taking latency hits, and disabled it, which helped a bunch.  I also
can't understand why it would be OK to interleave a normal task with an
RT task sometimes, but not others.. that's meaningless to the RT task.

IMHO, SMT scheduling should be a buyer beware thing.  Maximizing your
core utilization comes at a price, but so does disabling it, so I think
letting the user decide what he wants is the right thing to do.

	-Mike