Messages in this thread | | | Date | Mon, 15 Nov 2010 14:49:46 +1100 | From | Nick Piggin <> | Subject | Re: [patches] seqlock: add barrier-less special cases for seqcounts |
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On Fri, Nov 12, 2010 at 03:52:55PM -0800, Linus Torvalds wrote: > On Fri, Nov 12, 2010 at 3:06 PM, Nick Piggin <npiggin@kernel.dk> wrote: > . ... > > seq2 = read_seqlock_begin(&child->d_seq); > > if (read_seqcount_retry(&dentry->d_seq, seq)) > > /* bail out */ > > So the only issue is that this particular back-to-back sequence with > these kinds of "take one seqlock and release the previous one" where > you currently end up having basically one smp_rmb() at the end of > "read_seqlock_begin()", only to be followed immediately by another one > starting out the "read_seqcount_retry()"?
I think basically yes, I'll have to take another look at the code.
> If so, I think we should make _that_ operation ("move from one seqlock > to another") be the special one, because it smells like in general, > using the special non-locking versions is going to be a very subtle > interface.
OK, that sounds like a good idea. I'll see if that's applicable.
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