From: Thomas Gleixner <tglx@linutronix.de>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Guan Xuetao <gxt@mprc.pku.edu.cn>,
Paul Mundt <lethal@linux-sh.org>,
linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org
Subject: Re: [PATCH] unicore32 fix: remove arch-specific futex support
Date: Wed, 30 Mar 2011 14:50:29 +0200 (CEST) [thread overview]
Message-ID: <alpine.LFD.2.00.1103301446110.22418@localhost6.localdomain6> (raw)
In-Reply-To: <201103301440.03479.arnd@arndb.de>
On Wed, 30 Mar 2011, Arnd Bergmann wrote:
> On Wednesday 30 March 2011, Thomas Gleixner wrote:
> > The problem is that you need cmpxchg in user space as well.
> >
> > ARM does this with some syscall magic for machines which do not have
> > cmpxchg.
>
> Ah, right. I wonder how sh does it.
>
> I also remember that the original unicore32 ABI had support for a cmpxchg
> system call, but that was removed with the move to the generic syscall
> table.
>
> It is of course possible to add it back using the __NR_arch_specific_syscall
> entry point.
Either that or you take a trap. None of them is pretty.
If the only purpose is futex support, then we can add an extra flag to
the futex ops and handle it there via asm-generic/futex.h. That would
avoid an extra syscall in the contended case.
Thanks,
tglx
next prev parent reply other threads:[~2011-03-30 12:50 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-03-30 8:48 Guan Xuetao
2011-03-30 12:17 ` Arnd Bergmann
2011-03-30 12:27 ` Thomas Gleixner
2011-03-30 12:40 ` Arnd Bergmann
2011-03-30 12:50 ` Thomas Gleixner [this message]
2011-03-31 10:16 ` Guan Xuetao
2011-04-01 9:09 ` Arnd Bergmann
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