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

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Message-ID: <20090804145909.GO7746@elte.hu>
Date:	Tue, 4 Aug 2009 16:59:09 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Jason Wessel <jason.wessel@...driver.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	lkml <linux-kernel@...r.kernel.org>,
	"Deng, Dongdong" <Dongdong.Deng@...driver.com>
Subject: Re: [PATCH] softlockup: fix problem with long kernel pauses
	fromkgdb


* 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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