Re: [PATCH 0/3] 64-bit futexes: Intro

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To: Linus Torvalds <torvalds@...>
Cc: <linux-kernel@...>, <akpm@...>, <mtk.manpages@...>
Date: Saturday, May 31, 2008 - 12:38 am

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Linus Torvalds wrote:

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 have to disappoint you.  I thought of that and had to reject it.

- --
➧ Ulrich Drepper ➧ Red Hat, Inc. ➧ 444 Castro St ➧ Mountain View, CA ❖
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Messages in current thread:
[PATCH 0/3] 64-bit futexes: Intro, Ulrich Drepper, (Fri May 30, 9:27 pm)
Re: [PATCH 0/3] 64-bit futexes: Intro, Linus Torvalds, (Fri May 30, 10:13 pm)
Re: [PATCH 0/3] 64-bit futexes: Intro, Ulrich Drepper, (Fri May 30, 11:14 pm)
Re: [PATCH 0/3] 64-bit futexes: Intro, Linus Torvalds, (Fri May 30, 11:44 pm)
Re: [PATCH 0/3] 64-bit futexes: Intro, Ulrich Drepper, (Sat May 31, 12:04 am)
Re: [PATCH 0/3] 64-bit futexes: Intro, Linus Torvalds, (Sat May 31, 12:16 am)
Re: [PATCH 0/3] 64-bit futexes: Intro, Linus Torvalds, (Sat May 31, 12:23 am)
Re: [PATCH 0/3] 64-bit futexes: Intro, Ulrich Drepper, (Sat May 31, 12:38 am)
Re: [PATCH 0/3] 64-bit futexes: Intro, Linus Torvalds, (Sat May 31, 6:25 pm)
Re: [PATCH 0/3] 64-bit futexes: Intro, Ingo Molnar, (Mon Jun 2, 2:54 pm)
Re: [PATCH 0/3] 64-bit futexes: Intro, Linus Torvalds, (Mon Jun 2, 4:22 pm)
Re: [PATCH 0/3] 64-bit futexes: Intro, Nick Piggin, (Thu Jun 5, 9:27 pm)
Re: [PATCH 0/3] 64-bit futexes: Intro, Linus Torvalds, (Thu Jun 5, 11:37 pm)
Re: [PATCH 0/3] 64-bit futexes: Intro, Nick Piggin, (Fri Jun 6, 7:53 am)
Re: [PATCH 0/3] 64-bit futexes: Intro, Linus Torvalds, (Fri Jun 6, 11:01 am)
Re: [PATCH 0/3] 64-bit futexes: Intro, Ingo Molnar, (Mon Jun 2, 7:03 pm)
Re: [PATCH 0/3] 64-bit futexes: Intro, Nick Piggin, (Mon Jun 2, 11:24 pm)
Re: [PATCH 0/3] 64-bit futexes: Intro, Linus Torvalds, (Wed Jun 4, 3:57 pm)
Re: [PATCH 0/3] 64-bit futexes: Intro, Nick Piggin, (Wed Jun 4, 9:45 pm)
Re: [PATCH 0/3] 64-bit futexes: Intro, Linus Torvalds, (Wed Jun 4, 4:38 pm)
Re: [PATCH 0/3] 64-bit futexes: Intro, Nick Piggin, (Wed Jun 4, 9:56 pm)
Re: [PATCH 0/3] 64-bit futexes: Intro, Linus Torvalds, (Wed Jun 4, 11:08 pm)
Re: [PATCH 0/3] 64-bit futexes: Intro, Nick Piggin, (Thu Jun 5, 12:29 am)
Re: [PATCH 0/3] 64-bit futexes: Intro, Nick Piggin, (Wed Jun 4, 9:58 pm)
Re: [PATCH 0/3] 64-bit futexes: Intro, Linus Torvalds, (Sat May 31, 6:32 pm)
Re: [PATCH 0/3] 64-bit futexes: Intro, Linus Torvalds, (Sat May 31, 12:58 am)