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SubjectRe: [PATCH 0/3] sched: newidle and RT wake-buddy fixes
>>> On Mon, Jun 30, 2008 at  9:15 AM, in message <20080630131511.GA7506@elte.hu>,
Ingo Molnar <mingo@elte.hu> wrote:

> * Gregory Haskins <ghaskins@novell.com> wrote:
>
>> Hi Ingo,
>> The following patches apply to linux-tip/sched/devel and enhance the
>> performance of the kernel (specifically in PREEMPT_RT, though they do
>> not regress mainline performance as far as I can tell). They offer
>> somewhere between 50-100% speedups in netperf performance, depending
>> on the test.
>
> -tip testing found this boot hang:

Ok, I dug in a little bit here. I haven't verified this out yet, but I think the problem is that
your config is PREEMPT_VOLUNTARY which NOPs the preempt_disable() in schedule() that
I rely on to allow the lock to be dropped. (Doh!)

One way I can fix this is to fixup the newidle() code to only play the irq dropping tricks
ifdef CONFIG_PREEMPT == TRUE. Does this sound reasonable, or is there a better way
to address this?

-Greg

>
> Linux version 2.6.26-rc8-tip (mingo@dione) (gcc version 4.2.3) #12917
> SMP Mon Jun 30 15:06:32 CEST 2008
> [...]
> CPU 1/1 -> Node 0
> CPU: Physical Processor ID: 0
> CPU: Processor Core ID: 1
> CPU1: AMD Athlon(tm) 64 X2 Dual Core Processor 3800+ stepping 02
> Brought up 2 CPUs
> Total of 2 processors activated (8041.15 BogoMIPS).
> [ hard hang ]
>
> with this config:
>
> http://redhat.com/~mingo/misc/config-Mon_Jun_30_14_54_19_CEST_2008.bad
>
> full bootlog:
>
> http://redhat.com/~mingo/misc/hang-Mon_Jun_30_14_54_19_CEST_2008.bad
>
> it should continue with this bootup sequence:
>
> calling net_ns_init+0x0/0x1a0
> net_namespace: 376 bytes
> initcall net_ns_init+0x0/0x1a0 returned 0 after 0 msecs
> calling init_smp_flush+0x0/0x60
>
> i've bisected it down to:
>
> --------------
> | commit cc8160c56843201891766660e3816d2e546c1b17
> | Author: Gregory Haskins <ghaskins@novell.com>
> | Date: Fri Jun 27 14:29:50 2008 -0600
> |
> | sched: enable interrupts and drop rq-lock during newidle balancing
> --------------
>
> so i've reverted that change for now.
>
> Ingo




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