Re: [PATCH] rcupdate: move synchronize_sched() back to rcupdate.c V2

["Paul E. McKenney" <paulmck@linux.vnet.ibm.com>]

On Tue, Nov 11, 2008 at 08:55:00AM +0800, Lai Jiangshan wrote:
> 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.

Sounds good -- and thank you for your much-needed efforts to improve
the RCU implementation!

							Thanx, Paul