From: Brent Cook <bcook@bpointsys•com>
To: Tom Rini <trini@kernel•crashing.org>
Cc: linuxppc-embedded@ozlabs•org
Subject: Re: [PATCH] Export PowerPC atomic operations to userspace
Date: Mon, 15 May 2006 13:18:50 -0500 [thread overview]
Message-ID: <200605151318.50251.bcook@bpointsys.com> (raw)
In-Reply-To: <20060515171629.GC22868@smtp.west.cox.net>
On Monday 15 May 2006 12:16, Tom Rini wrote:
> On Mon, May 15, 2006 at 11:54:52AM -0500, Brent Cook wrote:
> > The atomic operations in asm/atomic.h are really useful from userspace
> > too. Other architectures (i386, x86_64, mips) export these to userspace,
> > but the powerpc versions are guarded by __KERNEL__ for some reason. Can
> > we remove these if there is no good reason to guard them?
> >
> > Signed-off-by: Brent Cook <bcook@bpointsys•com>
>
> NAK. i386, x86_64 and mips are broken in this regard. Please google up
> the previous threads that explain why you can't always get atomic
> operations on all architectures and why exporting this is bad.
OK, I see that possibly the only reason atomic_t is even exported is so that
sem.h works. Hopefully sem.h will get fixed and people like me will not be
even tempted by atomic.h.
What I really want is just a standard way to do atomic inc/dec in userspace;
I'm sure that people are going to continue wanting to have atomic_t
workalikes for their code.
After reading this thread:
http://www.developerweb.net/forum/archive/index.php/t-3294.html
it appears that just wrapping an integer in a pthreads mutex on an NPTL
machine wouldn't be much more overhead than using an atomic_t directly.
Looking at glibc's sources for powerpc nptl:
nptl/sysdeps/unix/sysv/linux/powerpc/lowlevellock.h
confirms that a futex lock is really similar to an atomic_t.
Thanks!
- Brent
prev parent reply other threads:[~2006-05-15 18:18 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-05-15 16:54 [PATCH] Export PowerPC atomic operations to userspace Brent Cook
2006-05-15 17:16 ` Tom Rini
2006-05-15 18:18 ` Brent Cook [this message]
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