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Date: Fri, 15 Mar 2002 16:04:44 +0000
From: Joel Becker <jlbec@evilplan.org>
To: Hubertus Franke <frankeh@watson.ibm.com>
Cc: Joel Becker <jlbec@evilplan.org>, Rusty Russell <rusty@rustcorp.com.au>,
        matthew@hairy.beasts.org, linux-kernel@vger.kernel.org,
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Subject: Re: [PATCH] Re: futex and timeouts
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On Fri, Mar 15, 2002 at 10:16:02AM -0500, Hubertus Franke wrote:
> > 	Why waste a syscall?  The user is going to be using a library
> > wrapper.  They don't have to know that futex_up() calls sys_futex(futex,
> > FUTEX_UP, NULL);
> 
> I agree with that, only for the reason that we are getting scarce on 
> syscall nubmers. Is 256-delta the max ?

	This was my impression, and why I called it "wasting" a syscall.
On architectures where syscall numbers or handles are unlimited, of
course there is no reason to keep it to one syscall.

> One thing to consider is that many don't want to use libraries.
> They want to inline, which would result only in a few instruction.

	Inlined you only take the penalty from the argument pushes.  You
still have to go through the motions of checking whether you can
get/release the lock in userspace.

> What I would like to see is an interface that lets me pass optional 
> parameters to the syscall interface, so I can call with different number
> of parameters.

	Is this to lock multiple futexes "atomically"?  If we are
looking for a fast path stack-wise, this seems extra work.

Joel

-- 

"Friends may come and go, but enemies accumulate." 
        - Thomas Jones

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