From: Nick Piggin <npiggin@suse.de>
To: Joel Schopp <jschopp@austin.ibm.com>
Cc: Nick Piggin <npiggin@suse.de>, Linus Torvalds <torvalds@osdl.org>,
Andrew Morton <akpm@osdl.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [patch 2/2] powerpc: native atomic_add_unless
Date: Thu, 19 Jan 2006 15:04:29 +0100 [thread overview]
Message-ID: <20060119140429.GC958@wotan.suse.de> (raw)
In-Reply-To: <43CEAD95.5010601@austin.ibm.com>
On Wed, Jan 18, 2006 at 03:05:25PM -0600, Joel Schopp wrote:
> >>Why use a separate register here? Why not reuse %0 instead of using %1?
> >>Registers are valuable.
> >>
> >You still need to get the output (t) because you need to return
> >whether the operation met with the "unless" case or not. If there is
> >a better way to do this then I'd like to know.
>
> I was thinking something like this would do:
>
> static __inline__ int atomic_add_unless(atomic_t *v, int a, int u)
> {
> int t;
>
> __asm__ __volatile__ (
> LWSYNC_ON_SMP
> "1: lwarx %0,0,%1 # atomic_add_unless\n\
> cmpw %0,%3 \n\
> beq- 2f \n\
> add %0,%2,%0 \n"
> PPC405_ERR77(0,%1)
> " stwcx. %0,0,%1 \n\
> bne- 1b \n"
> ISYNC_ON_SMP
> "subf %0,%2,%0 \n\
> 2:"
> : "=&r" (t)
> : "r" (&v->counter), "r" (a), "r" (u)
> : "cc", "memory");
>
> return likely(t != u);
> }
>
Oh yes, for some reason I thought that wouldn't work in all cases,
but I think that's nice. Thanks!
> Though if I could figure out how to get gcc to do it I'd much rather do
> something like this (which won't compile but I think illustrates the
> concept):
>
> static __inline__ int atomic_add_unless(atomic_t *v, int a, int u)
> {
> int t;
>
> __asm__ __volatile__ (
> LWSYNC_ON_SMP
> "1: lwarx %0,0,%1 # atomic_add_unless\n\
> cmpw %0,%3 \n\
> beq- 3f \n\
> add %0,%2,%0 \n"
> PPC405_ERR77(0,%1)
> " stwcx. %0,0,%1 \n\
> bne- 1b \n"
> ISYNC_ON_SMP
> 2:"
> : "=&r" (t)
> : "r" (&v->counter), "r" (a), "r" (u)
> : "cc", "memory");
>
> return 1;
> 3:
> return 0;
> }
next prev parent reply other threads:[~2006-01-19 14:04 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-01-18 6:36 [patch 1/2] atomic_add_unless sadness Nick Piggin
2006-01-18 6:39 ` [patch 2/2] powerpc: native atomic_add_unless Nick Piggin
2006-01-18 17:11 ` Joel Schopp
2006-01-18 17:28 ` Nick Piggin
2006-01-18 21:05 ` Joel Schopp
2006-01-19 14:04 ` Nick Piggin [this message]
2006-01-18 16:48 ` [patch 1/2] atomic_add_unless sadness Linus Torvalds
2006-01-18 17:10 ` Nick Piggin
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