From: will.deacon@arm•com (Will Deacon)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH 2/4] ARM: atomic ops: reduce critical region in atomic64_cmpxchg
Date: Thu, 8 Jul 2010 10:43:31 +0100 [thread overview]
Message-ID: <004c01cb1e82$070aa130$151fe390$@deacon@arm.com> (raw)
In-Reply-To: <alpine.LFD.2.00.1007080045450.6020@xanadu.home>
Hello,
> > diff --git a/arch/arm/include/asm/atomic.h b/arch/arm/include/asm/atomic.h
> > index e9e56c0..4f0f282 100644
> > --- a/arch/arm/include/asm/atomic.h
> > +++ b/arch/arm/include/asm/atomic.h
> > @@ -358,8 +358,8 @@ static inline u64 atomic64_cmpxchg(atomic64_t *ptr, u64 old, u64 new)
> >
> > do {
> > __asm__ __volatile__("@ atomic64_cmpxchg\n"
> > - "ldrexd %1, %H1, [%2]\n"
> > "mov %0, #0\n"
> > + "ldrexd %1, %H1, [%2]\n"
> > "teq %1, %3\n"
> > "teqeq %H1, %H3\n"
> > "strexdeq %0, %4, %H4, [%2]"
>
> I'm not sure you gain anything here. The ldrexd probably requires at
> least one result delay cycle which is filled by the mov instruction.
> By moving the mov insn before the ldrexd you are probably making the
> whole sequence one cycle longer.
You're right. In fact, thinking about it, this patch is largely
superficial because if the core can do exclusive load/stores then
the mov will be issued down a separate pipeline anyway.
I'll drop this one from the patch series and submit the other three.
Thanks,
Will
next prev parent reply other threads:[~2010-07-08 9:43 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-06-30 14:04 [PATCH 0/4] Fix atomic operations so that atomic64_test passes on ARM [V2] Will Deacon
2010-06-30 14:04 ` [PATCH 1/4] ARM: atomic ops: fix register constraints for atomic64_add_unless Will Deacon
2010-06-30 14:04 ` [PATCH 2/4] ARM: atomic ops: reduce critical region in atomic64_cmpxchg Will Deacon
2010-06-30 14:04 ` [PATCH 3/4] ARM: atomic ops: add memory constraints to inline asm Will Deacon
2010-06-30 14:04 ` [PATCH 4/4] ARM: atomic64_test: add ARM as supported architecture Will Deacon
2010-07-08 5:50 ` Nicolas Pitre
2010-07-07 16:42 ` [PATCH 3/4] ARM: atomic ops: add memory constraints to inline asm Will Deacon
2010-07-08 5:49 ` Nicolas Pitre
2010-07-08 9:36 ` Will Deacon
[not found] ` <004b01cb1e81$0b745960$225d0c20$%deacon@arm.com>
2010-07-08 12:42 ` Nicolas Pitre
[not found] ` <004101cb1df3$5825ecd0$0871c670$%deacon@arm.com>
2010-07-08 5:58 ` Nicolas Pitre
2010-07-08 10:03 ` Will Deacon
2010-07-08 4:49 ` [PATCH 2/4] ARM: atomic ops: reduce critical region in atomic64_cmpxchg Nicolas Pitre
2010-07-08 9:43 ` Will Deacon [this message]
2010-07-08 4:37 ` [PATCH 1/4] ARM: atomic ops: fix register constraints for atomic64_add_unless Nicolas Pitre
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