linux-kernel - Re: [PATCH] rcupdate: move synchronize

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Date:	Mon, 10 Nov 2008 11:22:15 +0800
From:	Lai Jiangshan <laijs@...fujitsu.com>
To:	paulmck@...ux.vnet.ibm.com
CC:	Ingo Molnar <mingo@...e.hu>, Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] rcupdate: move synchronize_sched() back to rcupdate.c
 V2

Paul E. McKenney wrote:
> On Thu, Nov 06, 2008 at 02:47:44PM +0800, Lai Jiangshan wrote:
>> this fix remove ugly macro, and increase readability for rcupdate codes
>>
>> changed from v1:
>> use HAVE_SPECIAL_RCU_BH/SCHED instead of define duplicate version of
>> synchronize_sched().
> 
> Hello, Jiangshan!
> 
> I very much like getting rid of the ugly macro.  I of course like the
> kernel-doc fixes.  ;-)
> 
> I am not yet convinced of the HAVE_SPECIAL_RCU_BH and
> HAVE_SPECIAL_RCU_SCHED pieces.  It is not clear to me that this approach
> is simpler than the current approach of simply providing the appropriate
> definitions for the symbols in the implementation-specific rcuxxx.h
> file.
> 
> Am I missing something?
> 
> 							Thanx, Paul
> 

I think:

RCU_BH is not required, we can used RCU instead. so HAVE_SPECIAL_RCU_BH
will help for implementation which has not RCU_BH.

HAVE_SPECIAL_RCU_SCHED is a little different, RCU and RCU_SCHED are both
required for the kernel. But I think, in an implementation,
if rcu_read_lock_sched() implies rcu_read_lock(), we may not need implement
RCU_SCHED too(sometimes we may implement RCU_SCHED for performance).
so HAVE_SPECIAL_RCU_SCHED will help.

Thanx, Lai.


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