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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Peter Zijlstra <peterz@infradead.org>
Cc: linux-kernel@vger.kernel.org, tglx@linutronix.de,
	Ingo Molnar <mingo@redhat.com>,
	Anna-Maria Gleixner <anna-maria@linutronix.de>,
	Richard Henderson <rth@twiddle.net>,
	Ivan Kokshaysky <ink@jurassic.park.msu.ru>,
	Matt Turner <mattst88@gmail.com>,
	linux-alpha@vger.kernel.org
Subject: Re: [PATCH 1.5/5] alpha: atomic: provide asm for the fastpath for _atomic_dec_and_lock_irqsave
Date: Mon, 4 Jun 2018 14:55:20 +0200	[thread overview]
Message-ID: <20180604125520.pkxvwg4sjlws2lrs@linutronix.de> (raw)
In-Reply-To: <20180604114852.GQ12217@hirez.programming.kicks-ass.net>

On 2018-06-04 13:48:52 [+0200], Peter Zijlstra wrote:
> On Mon, Jun 04, 2018 at 12:27:57PM +0200, Sebastian Andrzej Siewior wrote:
> > I just looked at Alpha's atomic_dec_and_lock assembly and did something
> > that should work for atomic_dec_and_lock_irqsave. I think it works but I
> > would prefer for someone from the Alpha-Camp to ack this before it goes
> > in. It is not critical because the non-optimized version should work.
> 
> I would vote to simply delete this entire file and get alpha on the
> generic code.
> 
> Afaict, this asm gets the ordering wrong, and I doubt it is much faster
> than using atomic_add_unless() in any case (+- the ordering of course).

I *think* the Alpha version is slightly wrong here. It does
	load
	dec by one
	cmpeq

while the __atomic_add_unless() implementation does
	load
	cmpeq
	
which is the right thing (unless I can't parse the assembly properly).

Sebastian

  reply	other threads:[~2018-06-04 12:55 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-04 15:45 Introduce atomic_dec_and_lock_irqsave() Sebastian Andrzej Siewior
2018-05-04 15:45 ` [PATCH 1/5] spinlock: atomic_dec_and_lock: Add an irqsave variant Sebastian Andrzej Siewior
2018-06-04 10:25   ` [PATCH 1/5 v2] " Sebastian Andrzej Siewior
2018-06-04 10:27     ` [PATCH 1.5/5] alpha: atomic: provide asm for the fastpath for _atomic_dec_and_lock_irqsave Sebastian Andrzej Siewior
2018-06-04 11:48       ` Peter Zijlstra
2018-06-04 12:55         ` Sebastian Andrzej Siewior [this message]
2018-06-06 11:18         ` [PATCH 0.5/5] alpha: remove custom dec_and_lock() implementation Sebastian Andrzej Siewior
2018-06-06 11:21           ` Sebastian Andrzej Siewior
2018-06-06 11:59           ` Peter Zijlstra
2018-06-12 21:36             ` [tip:locking/urgent] alpha: Remove " tip-bot for Sebastian Andrzej Siewior
2018-05-04 15:45 ` [PATCH 2/5] mm/backing-dev: Use irqsave variant of atomic_dec_and_lock() Sebastian Andrzej Siewior
2018-05-04 15:45 ` [PATCH 3/5] kernel/user: " Sebastian Andrzej Siewior
2018-05-04 15:45 ` [PATCH 4/5] drivers/md/raid5: " Sebastian Andrzej Siewior
2018-05-04 15:45 ` [PATCH 5/5] drivers/md/raid5: Do not disable irq on release_inactive_stripe_list() call Sebastian Andrzej Siewior
2018-05-04 15:54 ` Introduce atomic_dec_and_lock_irqsave() Peter Zijlstra
2018-05-04 16:07   ` Sebastian Andrzej Siewior
2018-05-04 16:21     ` Peter Zijlstra
2018-05-04 16:26       ` Al Viro
2018-05-04 16:38         ` Peter Zijlstra
2018-05-23 13:02 ` Peter Zijlstra
2018-05-30  9:26   ` Sebastian Andrzej Siewior

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