Re: [PATCH] "volatile considered harmful", take 3
- From: "H. Peter Anvin" <hpa@xxxxxxxxx>
- Date: Fri, 11 May 2007 22:34:13 -0700
Satyam Sharma wrote:
+ - Pointers to data structures in coherent memory which might be
modified
+ by I/O devices can, sometimes, legitimately be volatile. A ring
buffer
+ used by a network adapter, where that adapter changes pointers to
+ indicate which descriptors have been processed, is an example of
this
+ type of situation.
is a legitimate use case for volatile is still not clear to me (I
agree with Alan's
comment in a previous thread that this seems to be a case where a memory
barrier would be applicable^Wbetter, actually). I could be wrong here, so
would be nice if Peter explains why volatile is legitimate here.
Otherwise, it's fine with me.
I don't see why Alan's way is necessarily better; it should work but is
more heavy-handed as it's disabling *all* optimization such as loop
invariants across the barrier.
-hpa
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