RE: Synchronizing Bit operations V2

From: Christoph Lameter <>
Date: 2006-03-31 12:13:07
On Thu, 30 Mar 2006, Chen, Kenneth W wrote:

> > Arch specific code should make this explicit too and not rely on implied 
> > semantics. Otherwise one has to memorize that functions have to work with 
> > different semantics in arch code and core code which makes the source 
> > code difficult to maintain.
> I don't know whether we are talking about the same thing: I propose for 
> ia64: 
>clear_bit to have release semantic,

Inconsistent with other bit operations.

>smp_mb__before_clear_bit will be a noop,

Then there will no barrier since clear_bit only has acquire semantics. This is a 
bug in bit operations since smb_mb__before_clear_bit does not work as 

>smp_mb_after_clear_bit will be a smp_mb().


> Caller are still required to use smp_mb__before_clear_bit if it requires, on
> ia64, that function will simply be a noop.

Well ultimately I wish we could move away from these 
smb_mb__before/after_xx macros and use explicit synchronization ordering 

If there is agreement on this patch then we can use explicit ordering in 
core kernel code and slowly get rid of smb_mb__xxx.

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Received on Fri Mar 31 12:14:18 2006

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