From: Hubertus Franke <frankeh@watson.ibm.com>
To: Joel Becker <jlbec@evilplan.org>
Cc: Joel Becker <jlbec@evilplan.org>,
Rusty Russell <rusty@rustcorp.com.au>,
matthew@hairy.beasts.org, linux-kernel@vger.kernel.org,
lse-tech@lists.sourceforge.net
Subject: Re: [PATCH] Re: futex and timeouts
Date: Fri, 15 Mar 2002 13:59:38 -0500 [thread overview]
Message-ID: <20020315185844.8883E3FE06@smtp.linux.ibm.com> (raw)
In-Reply-To: <20020314151846.EDCBF3FE07@smtp.linux.ibm.com> <20020315151507.2370C3FE0C@smtp.linux.ibm.com> <20020315160444.P4836@parcelfarce.linux.theplanet.co.uk>
In-Reply-To: <20020315160444.P4836@parcelfarce.linux.theplanet.co.uk>
On Friday 15 March 2002 11:04 am, Joel Becker wrote:
> 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
No, take for example...
syscall3(int,futex,int,op, struct futex*, futex, int opt_arg);
I will be always forced by the compiler (-Wall) to supply 3 arguments even
as in the case of "no time out desired" I have to push a 3rd meaningless
optional argument on the stack.
--
-- Hubertus Franke (frankeh@watson.ibm.com)
next prev parent reply other threads:[~2002-03-15 18:59 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2002-03-13 18:26 futex and timeouts Hubertus Franke
2002-03-13 18:54 ` Ulrich Drepper
2002-03-14 4:15 ` Rusty Russell
2002-03-14 15:19 ` Hubertus Franke
2002-03-15 5:39 ` [PATCH] " Rusty Russell
2002-03-15 6:08 ` Joel Becker
2002-03-15 6:56 ` H. Peter Anvin
2002-03-15 8:49 ` Rusty Russell
2002-03-15 15:16 ` Hubertus Franke
2002-03-15 16:04 ` Joel Becker
2002-03-15 18:59 ` Hubertus Franke [this message]
2002-03-15 19:28 ` Joel Becker
2002-03-16 1:12 ` [Lse-tech] " george anzinger
2002-03-18 21:35 ` Hubertus Franke
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