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From: Will Deacon <will@kernel.org>
To: Herbert Xu <herbert@gondor.apana.org.au>
Cc: linux@armlinux.org.uk, torvalds@linux-foundation.org,
	catalin.marinas@arm.com, vincent.whitchurch@axis.com,
	axboe@kernel.dk, linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org, rabinv@axis.com,
	Richard.Earnshaw@arm.com
Subject: Re: [PATCH v2] buffer: Fix I/O error due to ARM read-after-read hazard
Date: Thu, 21 Nov 2019 16:53:35 +0000	[thread overview]
Message-ID: <20191121165334.GB4905@willie-the-truck> (raw)
In-Reply-To: <20191121012533.3h6akm4oczswj7zr@gondor.apana.org.au>

On Thu, Nov 21, 2019 at 09:25:33AM +0800, Herbert Xu wrote:
> On Wed, Nov 20, 2019 at 07:18:40PM +0000, Will Deacon wrote:
> >
> > > The Alpha barrier matters for pointers, how could it make a
> > > difference for individual bits?
> > 
> > I guess you could use the result of test_bit to index into an array or
> > something?
> 
> Can Alpha Assembly even do this without using a branch?

Don't see why not: you can add the base address to the scaled result
of test_bit and use that as the address register into a load instruction.

Will

WARNING: multiple messages have this Message-ID (diff)
From: Will Deacon <will@kernel.org>
To: Herbert Xu <herbert@gondor.apana.org.au>
Cc: axboe@kernel.dk, Richard.Earnshaw@arm.com, rabinv@axis.com,
	catalin.marinas@arm.com, vincent.whitchurch@axis.com,
	linux@armlinux.org.uk, linux-kernel@vger.kernel.org,
	torvalds@linux-foundation.org,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v2] buffer: Fix I/O error due to ARM read-after-read hazard
Date: Thu, 21 Nov 2019 16:53:35 +0000	[thread overview]
Message-ID: <20191121165334.GB4905@willie-the-truck> (raw)
In-Reply-To: <20191121012533.3h6akm4oczswj7zr@gondor.apana.org.au>

On Thu, Nov 21, 2019 at 09:25:33AM +0800, Herbert Xu wrote:
> On Wed, Nov 20, 2019 at 07:18:40PM +0000, Will Deacon wrote:
> >
> > > The Alpha barrier matters for pointers, how could it make a
> > > difference for individual bits?
> > 
> > I guess you could use the result of test_bit to index into an array or
> > something?
> 
> Can Alpha Assembly even do this without using a branch?

Don't see why not: you can add the base address to the scaled result
of test_bit and use that as the address register into a load instruction.

Will

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http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  reply	other threads:[~2019-11-21 16:53 UTC|newest]

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-12 13:02 [PATCH v2] buffer: Fix I/O error due to ARM read-after-read hazard Vincent Whitchurch
2019-11-12 13:02 ` Vincent Whitchurch
2019-11-12 16:08 ` Catalin Marinas
2019-11-12 16:08   ` Catalin Marinas
2019-11-12 17:54   ` Linus Torvalds
2019-11-12 17:54     ` Linus Torvalds
2019-11-12 18:00   ` Will Deacon
2019-11-12 18:00     ` Will Deacon
2019-11-12 18:22     ` Catalin Marinas
2019-11-12 18:22       ` Catalin Marinas
2019-11-12 18:39       ` Linus Torvalds
2019-11-12 18:39         ` Linus Torvalds
2019-11-13 10:23         ` Will Deacon
2019-11-13 10:23           ` Will Deacon
2019-11-13 10:31           ` Russell King - ARM Linux admin
2019-11-13 10:31             ` Russell King - ARM Linux admin
2019-11-13 10:49             ` Will Deacon
2019-11-13 10:49               ` Will Deacon
2019-11-14 13:28               ` Herbert Xu
2019-11-14 13:28                 ` Herbert Xu
2019-11-20 19:18                 ` Will Deacon
2019-11-20 19:18                   ` Will Deacon
2019-11-21  1:25                   ` Herbert Xu
2019-11-21  1:25                     ` Herbert Xu
2019-11-21 16:53                     ` Will Deacon [this message]
2019-11-21 16:53                       ` Will Deacon
2019-11-13 16:36           ` Linus Torvalds
2019-11-13 16:36             ` Linus Torvalds
2019-11-13 16:40             ` Linus Torvalds
2019-11-13 16:40               ` Linus Torvalds

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