Messages in this thread | | | Date | Fri, 30 May 2008 21:38:23 -0700 | From | Ulrich Drepper <> | Subject | Re: [PATCH 0/3] 64-bit futexes: Intro |
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Linus Torvalds wrote: > Is it possible? I dunno.
Once again not without limitations which are too low. The main problem is that there is far more information needed on the reader side. There are two counters and a number of bits for state information. Which means the counters can be at most 14 bits in size.
A counter this low also means I cannot unconditionally increment them (since there can be more than 2^14 threads sharing one page). This means you get in the cache line race I described in the last mail. You first have to load a word and then perform a the write operation while at the same time other threads competing with you for the same cache line.
> I personally suspect it is. I also suspect you > didn't even try.
I have to disappoint you. I thought of that and had to reject it.
- -- ➧ Ulrich Drepper ➧ Red Hat, Inc. ➧ 444 Castro St ➧ Mountain View, CA ❖ -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (GNU/Linux)
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