Re: [PATCH 0/2] jump label: 2.6.38 updates

[Mathieu Desnoyers]

* H. Peter Anvin (hpa@xxxxxxxxx) wrote:
> On 02/16/2011 05:55 PM, Masami Hiramatsu wrote:
> > 
> > Hmm, I think that is miss-coding ll/sc.
> > If I understand correctly, usually cache invalidation should be done
> > right before storing value, as MSI protocol does.
> > (or, sc should atomically invalidate the cache line)
> > 
> 
> I suspect in this case one should flush the cache line before ll (a
> cache flush will typically invalidate the ll/sc link.)

hrm, but if you have:

  invalidate
  -> interrupt
     read (fetch the invalidated cacheline)
  ll
  sc

you basically end up in a situation similar to not having any
invalidate, no ? AFAIU, disabling interrupts around the whole
ll-sc-invalidate (or invalidate-ll-sc) seems required for this specific
architecture, so the invalidation is made "atomic" with the ll-sc pair
from the point of view of one hardware thread.

Mathieu

> 
> 	-hpa
> 
> -- 
> H. Peter Anvin, Intel Open Source Technology Center
> I work for Intel.  I don't speak on their behalf.
> 

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com
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