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Date: Tue, 11 Nov 2008 08:55:00 +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 Mon, Nov 10, 2008 at 11:22:15AM +0800, Lai Jiangshan wrote: >> 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. > > If I understand correctly, this is the "old way": > > ------------------------------------------------------------------------ > > rcupdate.h: > > #define rcu_read_lock_bh() __rcu_read_lock_bh() > #define rcu_read_unlock_bh() __rcu_read_unlock_bh() > > rcupreempt.h: > > #define __rcu_read_lock_bh() { rcu_read_lock(); local_bh_disable(); } > #define __rcu_read_unlock_bh() { local_bh_enable(); rcu_read_unlock(); } > > ------------------------------------------------------------------------ > > And then this is the "new way": > > ------------------------------------------------------------------------ > > rcupdate.h: > > #ifdef HAVE_SPECIAL_RCU_BH > #define rcu_read_lock_bh() __rcu_read_lock_bh() > #define rcu_read_unlock_bh() __rcu_read_unlock_bh() > #else > #define __rcu_read_lock_bh() { rcu_read_lock(); local_bh_disable(); } > #define __rcu_read_unlock_bh() { local_bh_enable(); rcu_read_unlock(); } > #endif /* HAVE_SPECIAL_RCU_BH */ > > rcupreempt.h: > > #define HAVE_SPECIAL_RCU_BH > > ------------------------------------------------------------------------ > > If we had ten different RCU implementations, then the "new way" would save > a little bit of code. But the "old way" is a bit easier to figure out. > > So I am in favor of getting rid of the ugly macro, and also in favor > of fixing the kerneldoc, but opposed to the HAVE_SPECIAL_RCU_BH and > HAVE_SPECIAL_RCU_SCHED changes. I apprehended and agree with you. Thanx. Lai. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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