linux-kernel - Re: [RFC PATCH 4/5] RCU: Add TASK_RCU

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Message-ID: <20110407154737.GF2262@linux.vnet.ibm.com>
Date:	Thu, 7 Apr 2011 08:47:37 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Lai Jiangshan <laijs@...fujitsu.com>
Cc:	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Michal Marek <mmarek@...e.cz>,
	Jan Beulich <JBeulich@...ell.com>, Ingo Molnar <mingo@...e.hu>,
	Alexander van Heukelum <heukelum@...tmail.fm>,
	Dipankar Sarma <dipankar@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Sam Ravnborg <sam@...nborg.org>,
	David Howells <dhowells@...hat.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Roland McGrath <roland@...hat.com>,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [RFC PATCH 4/5] RCU: Add TASK_RCU_OFFSET

On Thu, Apr 07, 2011 at 01:49:51PM +0800, Lai Jiangshan wrote:
> On 04/07/2011 08:30 AM, Paul E. McKenney wrote:
> > On Wed, Apr 06, 2011 at 02:27:39PM -0700, H. Peter Anvin wrote:
> >> On 04/06/2011 02:06 PM, Peter Zijlstra wrote:
> >>> On Wed, 2011-04-06 at 13:13 -0700, Paul E. McKenney wrote:
> >>>> And the following patch builds correctly for defconfig x86 builds,
> >>>> while allowing rcupdate.h to see the sched.h definitions as needed
> >>>> to inline rcu_read_lock() and rcu_read_unlock().
> >>>>
> >>> Looks like an entirely reasonable patch to me ;-)
> >>>
> >>
> >> Quite... a lot better than the original proposal!
> > 
> > Glad you both like it!
> > 
> > When I do an allyesconfig build, I do get errors during the "CHECK"
> > phase, when it is putting things into the usr/include in the build tree.
> > I believe that this is because I am exposing different header files to
> > the library-export scripts.  The following patch silences some of them,
> > but I am really out of my depth here.
> > 
> > Sam, Jan, Michal, help?
> > 
> > 							Thanx, Paul
> > 
> > ------------------------------------------------------------------------
> > 
> 
> Easy to split rcupdate.h, hard to resolve the dependence problem.
> 
> You can apply the next additional patch when you test:

I am sure that you are quite correct.  ;-)

I am moving _rcu_read_lock() and _rcu_read_unlock() into
include/linux/rcutree.h and include/linux/rcutiny.h, and I am sure that
more pain will ensue.

One thing I don't understand...  How does is it helping to group the
task_struct RCU-related fields into a structure?  Is that generating
better code on your platform due to smaller offsets or something?

Also, does your patchset address the CHECK warnings?

							Thanx, Paul

> diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
> index 0b4496a..ccbebeb 100644
> --- a/include/linux/rcupdate.h
> +++ b/include/linux/rcupdate.h
> @@ -788,4 +788,10 @@ static inline void debug_rcu_head_unqueue(struct rcu_head *head)
>  #error "Unknown RCU implementation specified to kernel configuration"
>  #endif
> 
> +#include <linux/sched.h>
> +static inline long test_use_task_struct(void)
> +{
> +	return current->state;
> +}
> +
>  #endif /* __LINUX_RCUPDATE_H */
> --
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