Messages in this thread | | | Date | Mon, 10 Nov 2008 10:45:20 -0800 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH] rcupdate: move synchronize_sched() back to rcupdate.c V2 |
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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.
Or am I missing something?
Thanx, Paul
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