linux-kernel - Re: RCU_USER

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Date:	Thu, 4 Oct 2012 08:46:36 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Dave Jones <davej@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: RCU_USER_QS traces.

On Thu, Oct 04, 2012 at 10:41:06AM -0400, Dave Jones wrote:
>  > We have CONFIG_RCU_USER_QS that is a specific case. It's an intermediate state
>  > before we implement a true CONFIG_NO_HZ_FULL. But the option is useless on its
>  > own for users. Worse, it introduces a real overhead. OTOH we want it to be upstream
>  > to make the development of full tickless feature more incremental.
> 
> I couldn't resist trying it.. Did these get reported yet ?

News to me...  Thank you for the testing!

And yes, please do not enable CONFIG_RCU_USER_QS in your distro.  ;-)

							Thanx, Paul

> WARNING: at kernel/rcutree.c:377 rcu_eqs_enter+0x93/0xa0()
> Pid: 0, comm: swapper/1 Not tainted 3.6.0+ #24
> Call Trace:
>  [<ffffffff810678af>] warn_slowpath_common+0x7f/0xc0
>  [<ffffffff8106790a>] warn_slowpath_null+0x1a/0x20
>  [<ffffffff8111a383>] rcu_eqs_enter+0x93/0xa0
>  [<ffffffff8111af0b>] rcu_idle_enter+0x2b/0x70
>  [<ffffffff8102460f>] cpu_idle+0xbf/0x140
>  [<ffffffff816ad18d>] start_secondary+0x252/0x254
> 
> WARNING: at kernel/rcutree.c:352 rcu_eqs_enter_common.isra.37+0x1c6/0x1e0()
> Pid: 0, comm: swapper/1 Tainted: G        W    3.6.0+ #24
> Call Trace:
>  [<ffffffff810678af>] warn_slowpath_common+0x7f/0xc0
>  [<ffffffff8106790a>] warn_slowpath_null+0x1a/0x20
>  [<ffffffff8111a2d6>] rcu_eqs_enter_common.isra.37+0x1c6/0x1e0
>  [<ffffffff8111a355>] rcu_eqs_enter+0x65/0xa0
>  [<ffffffff8111af0b>] rcu_idle_enter+0x2b/0x70
>  [<ffffffff8102460f>] cpu_idle+0xbf/0x140
>  [<ffffffff816ad18d>] start_secondary+0x252/0x254
> 
> WARNING: at kernel/rcutree.c:539 rcu_eqs_exit+0x99/0xb0()
> Pid: 0, comm: swapper/1 Tainted: G        W    3.6.0+ #24
> Call Trace:
>  [<ffffffff810678af>] warn_slowpath_common+0x7f/0xc0
>  [<ffffffff8106790a>] warn_slowpath_null+0x1a/0x20
>  [<ffffffff8111a0f9>] rcu_eqs_exit+0x99/0xb0
>  [<ffffffff8111ae9b>] rcu_idle_exit+0x2b/0x70
>  [<ffffffff8102461e>] cpu_idle+0xce/0x140
>  [<ffffffff816ad18d>] start_secondary+0x252/0x254
> 
> WARNING: at kernel/rcutree.c:513 rcu_eqs_exit_common.isra.35+0xd4/0xe0()
> Pid: 0, comm: swapper/1 Tainted: G        W    3.6.0+ #24
> Call Trace:
>  [<ffffffff810678af>] warn_slowpath_common+0x7f/0xc0
>  [<ffffffff8106790a>] warn_slowpath_null+0x1a/0x20
>  [<ffffffff8111a054>] rcu_eqs_exit_common.isra.35+0xd4/0xe0
>  [<ffffffff8111a0bc>] rcu_eqs_exit+0x5c/0xb0
>  [<ffffffff8111ae9b>] rcu_idle_exit+0x2b/0x70
>  [<ffffffff8102461e>] cpu_idle+0xce/0x140
>  [<ffffffff816ad18d>] start_secondary+0x252/0x254
> 
> 	Dave
> 

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