linux-kernel - Re: [PATCH 01/02] remove set_wmb

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Date:	Fri, 14 Jul 2006 22:35:03 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Matthew Wilcox <matthew@....cx>
Cc:	Andrew Morton <akpm@...l.org>, Linus Torvalds <torvalds@...l.org>,
	mingo@...e.hu, linux-arch@...r.kernel.org,
	David Howells <dhowells@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 01/02] remove set_wmb - doc update

On Fri, 2006-07-14 at 20:22 -0600, Matthew Wilcox wrote:
> On Fri, Jul 14, 2006 at 04:05:01PM -0400, Steven Rostedt wrote:
> >  There are some more advanced barrier functions:
> >  
> >   (*) set_mb(var, value)
> > - (*) set_wmb(var, value)
> >  
> > -     These assign the value to the variable and then insert at least a write
> > -     barrier after it, depending on the function.  They aren't guaranteed to
> > +     This assigns the value to the variable and then inserts at least a write
> > +     barrier after it, depending on the function.  It isn't guaranteed to
> >       insert anything more than a compiler barrier in a UP compilation.
> 
> "There is one more advanced barrier function"?  ;-)  Or did you want to
> remove set_mb()?

Actually below the patch area we still have:

 (*) smp_mb__before_atomic_dec();
 (*) smp_mb__after_atomic_dec();
 (*) smp_mb__before_atomic_inc();
 (*) smp_mb__after_atomic_inc();

So that "There are" references them too :)

> 
> Plus, the "depending on the function" bit means "respectively".  So what
> you really want as help is something like:
> 
> 	This assigns the value to the variable and then inserts a
> 	barrier after the assignment.  It isn't guaranteed to insert
> 	anything more than a compiler barrier in a UP compilation.

OK, you're right here, that "depending on the function" needs to go.
Here's a better version:

Thanks,

-- Steve

Signed-off-by: Steven Rostedt <rostedt@...dmis.org>

Index: linux-2.6.18-rc1/Documentation/memory-barriers.txt
===================================================================
--- linux-2.6.18-rc1.orig/Documentation/memory-barriers.txt	2006-07-14 15:38:23.000000000 -0400
+++ linux-2.6.18-rc1/Documentation/memory-barriers.txt	2006-07-14 22:31:01.000000000 -0400
@@ -1015,11 +1015,10 @@ CPU from reordering them.
 There are some more advanced barrier functions:
 
  (*) set_mb(var, value)
- (*) set_wmb(var, value)
 
-     These assign the value to the variable and then insert at least a write
-     barrier after it, depending on the function.  They aren't guaranteed to
-     insert anything more than a compiler barrier in a UP compilation.
+     This assigns the value to the variable and then inserts a memory barrier
+     after it.  It isn't guaranteed to insert anything more than a compiler
+     barrier in a UP compilation.
 
 
  (*) smp_mb__before_atomic_dec();


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