Messages in this thread | | | Date | Mon, 18 Jun 2007 12:58:26 +0200 | From | Pierre Peiffer <> | Subject | Re: [PATCH] Futex: Revert the non-functional REQUEUE_PI |
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Thomas Gleixner wrote : > Patch d0aa7a70bf03b9de9e995ab272293be1f7937822 titled > > "futex_requeue_pi optimization" > > introduced user space visible changes to the futex syscall. > > The patch is non-functional and there is no way to fix it proper before > the 2.6.22 release. > > The breakage report ( http://lkml.org/lkml/2007/5/12/17 ) went > unanswered,
Sorry, but I passed lot of time on this last year without any answers or comments from the community when I have sent my patches. Now I'm working on something else and I can't spent more time on this for now... Futexes are so complex that it is always difficult to investigate a problem in only one or two hours...
> and unfortunately it turned out that the concept is not > feasible at all.
Without robust futex, the concept works well, and the performance gain has been proven.
It violates the rtmutex semantics badly by introducing > a virtual owner, which hacks around the coupling of the user-space > pi_futex and the kernel internal rt_mutex representation.
What you call a hack, is for me a design point. And if this is a hack, then I think that we can say that futexes are based on a series of hacks... But, okay, this is not very constructive, so...
Ulrich Drepper wrote : > > Indeed. A lot more discussion is needed to handle this correctly. No > committed code in glibc so far uses the function so removal is no problem.
Once again, it's a pity that people didn't spent time to comment on this when I was working on this. Now, the work will probably just be lost...
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