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From: Will Deacon <>
To: "Paul E. McKenney" <>
Cc: Alan Stern <>,
	Marco Elver <>, Boqun Feng <>,
	Andrea Parri <>,
	Mark Rutland <>,
	Dmitry Vyukov <>,,
Subject: Re: LKMM: Read dependencies of writes ordered by dma_wmb()?
Date: Tue, 17 Aug 2021 13:28:16 +0100	[thread overview]
Message-ID: <20210817122816.GA12746@willie-the-truck> (raw)
In-Reply-To: <20210816205057.GN4126399@paulmck-ThinkPad-P17-Gen-1>

Just on this bit...

On Mon, Aug 16, 2021 at 01:50:57PM -0700, Paul E. McKenney wrote:
> 5.	The dma_mb(), dma_rmb(), and dma_wmb() appear to be specific
> 	to ARMv8.

These are useful on other architectures too! IIRC, they were added by x86 in
the first place. They're designed to be used with dma_alloc_coherent()
allocations where you're sharing something like a ring buffer with a device
and they guarantee accesses won't be reordered before they become visible
to the device. They _also_ provide the same ordering to other CPUs.

I gave a talk at LPC about some of this, which might help (or might make
things worse...):

Ignore the bits about mmiowb() as we got rid of that.


  parent reply	other threads:[~2021-08-17 12:28 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-16 10:12 Marco Elver
2021-08-16 14:59 ` Alan Stern
2021-08-16 17:23   ` Marco Elver
2021-08-16 19:21     ` Alan Stern
2021-08-16 20:50       ` Paul E. McKenney
2021-08-17 12:14         ` Marco Elver
2021-08-17 12:28         ` Will Deacon [this message]
2021-08-17 13:27           ` Marco Elver
2021-08-17 13:53           ` Paul E. McKenney
2021-08-18 11:39             ` Will Deacon
2021-08-18 23:17               ` Paul E. McKenney

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