linux-kernel - Re: frequent lockups in 3.18rc4

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Date:	Fri, 19 Dec 2014 10:14:29 -0500
From:	Chris Mason <clm@...com>
To:	Dave Jones <davej@...hat.com>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Mike Galbraith <umgwanakikbuti@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Dâniel Fraga <fragabr@...il.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Suresh Siddha <sbsiddha@...il.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Peter Anvin <hpa@...ux.intel.com>
Subject: Re: frequent lockups in 3.18rc4



On Fri, Dec 19, 2014 at 9:55 AM, Dave Jones <davej@...hat.com> wrote:
> On Thu, Dec 18, 2014 at 08:48:24PM -0800, Linus Torvalds wrote:
>  > On Thu, Dec 18, 2014 at 8:03 PM, Dave Jones <davej@...hat.com> 
> wrote:
>  > >
>  > > So the only thing that was on that could cause spinlock overhead
>  > > was DEBUG_SPINLOCK (and LOCK_STAT, though iirc that's not huge 
> either)
>  >
>  > So DEBUG_SPINLOCK does have one big downside if I recall correctly 
> -
>  > the debugging spinlocks are very much not fair. So they don't work
>  > like the real ticket spinlocks. That might have serious effects on 
> the
>  > contention case, with some thread not making any progress due to 
> just
>  > the implementation of the debug spinlocks.
> 
> Wish DEBUG_SPINLOCK disabled, I see the same behaviour.
> Lots of traces spewed, but it seems to run and run (at least so far).

Not quite the same, the spinlocks are gone.

-chris



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