Re: [PATCH] Document Linux's memory barriers

[Robert Hancock <hancockr@shaw.ca>]

Jesse Barnes wrote:
> On Tuesday, March 7, 2006 10:30 am, David Howells wrote:
>> True, I suppose. I should make it clear that these accessor functions
>> imply memory barriers, if indeed they do, and that you should use them
>> rather than accessing I/O registers directly (at least, outside the
>> arch you should).
> 
> But they don't, that's why we have mmiowb().

I don't think that is why that function exists.. It's a no-op on most 
architectures, even where you would need to be able to do write barriers 
on IO accesses (i.e. x86_64 using CONFIG_UNORDERED_IO). I believe that 
function is intended for a more limited special case.

I think any complete memory barrier description should document that 
function as well as EXPLICITLY specifying whether or not the 
readX/writeX, etc. functions imply barriers or not.

> Btw, thanks for putting together this documentation, it's desperately 
> needed.

Seconded.. The fact that there's debate over what the rules even are 
shows why this is needed so badly.

-- 
Robert Hancock      Saskatoon, SK, Canada
To email, remove "nospam" from hancockr@nospamshaw.ca
Home Page: http://www.roberthancock.com/