linux-kernel - Re: [PATCH] softlockup: fix problem with long kernel pauses from kgdb

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Date:	Fri, 21 Aug 2009 20:42:21 +0800
From:	DDD <Dongdong.deng@...driver.com>
To:	Jason Wessel <jason.wessel@...driver.com>,
	Ingo Molnar <mingo@...e.hu>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] softlockup: fix problem with long kernel pauses from
	kgdb

Hi Jason & Ingo,

If we apply Peter's patch which was send out just a moment ago,
I believe this issue will gone.  :-) 

Thanks,
Dongdong


[PATCH -rt] timer: delay waking softirqs from the jiffy tick
...
...
Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
---
 kernel/timer.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/kernel/timer.c b/kernel/timer.c
index 8137cce..96ac1b4 100644
--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -1221,10 +1221,10 @@ void update_process_times(int user_tick)

       /* Note: this timer irq context must be accounted for as well. */
       account_process_tick(p, user_tick);
+       scheduler_tick();
       run_local_timers();
       if (rcu_pending(cpu))
               rcu_check_callbacks(cpu, user_tick);
-       scheduler_tick();
       run_posix_cpu_timers(p);
 }



On Tue, 2009-08-04 at 16:59 +0200, Ingo Molnar wrote: 
> * Jason Wessel <jason.wessel@...driver.com> wrote:
> 
> > Ingo Molnar wrote:
> > > * Jason Wessel <jason.wessel@...driver.com> wrote:
> > > 
> > >> -----
> > >> From: Jason Wessel <jason.wessel@...driver.com>
> > >> Subject: [PATCH] softlockup: add sched_clock_tick() to avoid kernel warning on kgdb resume
> > >>
> > >> When CONFIG_HAVE_UNSTABLE_SCHED_CLOCK is set sched_clock() gets the
> > >> time from hardware, such as from TSC.  In this configuration kgdb will
> > >> report a softlock warning messages on resuming or detaching from a
> > >> debug session.
> > >>
> > > 
> > > Hm, this looks quite ugly. Peter, Thomas, can you think of a 
> > > cleaner solution?
> > > 
> > 
> > Below was a more specific test case I received from Dongdong Deng 
> > which did not require kgdb.  The test case is not something to 
> > merge, it is just a simple module to build to demonstrate the 
> > problem outside of kgdb.
> > 
> > The patch I submitted might have been on the "ugly" side, but 
> > there was not an obvious way to solve the problem without making 
> > changes in kernel/sched*.  I opted for something that was entirely 
> > self contained to the softlockup code.
> 
> it's not really the fault of your patch really - all these 
> integrations along dynticks, scheduler time and softlockup feel a 
> bit awkward. Wondering whether there's some nicer way.
> 
> 	Ingo
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