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From: David Howells <dhowells@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: dhowells@redhat.com,
	Andrea Parri <andrea.parri@amarulasolutions.com>,
	linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
	Alan Stern <stern@rowland.harvard.edu>,
	Will Deacon <will.deacon@arm.com>,
	Boqun Feng <boqun.feng@gmail.com>,
	Nicholas Piggin <npiggin@gmail.com>,
	Jade Alglave <j.alglave@ucl.ac.uk>,
	Luc Maranget <luc.maranget@inria.fr>,
	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
	Akira Yokosawa <akiyks@gmail.com>,
	Daniel Lustig <dlustig@nvidia.com>,
	Jonathan Corbet <corbet@lwn.net>, Ingo Molnar <mingo@redhat.com>,
	Randy Dunlap <rdunlap@infradead.org>
Subject: Re: [PATCH] doc: Update wake_up() & co. memory-barrier guarantees
Date: Mon, 25 Jun 2018 13:12:45 +0100	[thread overview]
Message-ID: <2779.1529928765@warthog.procyon.org.uk> (raw)
In-Reply-To: <20180625095031.GX2494@hirez.programming.kicks-ass.net>

Peter Zijlstra <peterz@infradead.org> wrote:

> So yes, I suppose we're entirely suck with the full memory barrier
> semantics like that. But I still find it easier to think of it like a
> RELEASE that pairs with the ACQUIRE of waking up, such that the task
> is guaranteed to observe it's own wake condition.
> 
> And maybe that is the thing I'm missing here. These comments only state
> that it does in fact imply a full memory barrier, but do not explain
> why, should it?

I think because RELEASE and ACQUIRE concepts didn't really exist in Linux at
the time I wrote the doc, so the choices were read/readdep, write or full.

Since this document defines the *minimum* you can expect rather than what the
kernel actually gives you, I think it probably makes sense to switch to
RELEASE and ACQUIRE here.

David
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WARNING: multiple messages have this Message-ID (diff)
From: David Howells <dhowells@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: dhowells@redhat.com,
	Andrea Parri <andrea.parri@amarulasolutions.com>,
	linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
	Alan Stern <stern@rowland.harvard.edu>,
	Will Deacon <will.deacon@arm.com>,
	Boqun Feng <boqun.feng@gmail.com>,
	Nicholas Piggin <npiggin@gmail.com>,
	Jade Alglave <j.alglave@ucl.ac.uk>,
	Luc Maranget <luc.maranget@inria.fr>,
	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
	Akira Yokosawa <akiyks@gmail.com>,
	Daniel Lustig <dlustig@nvidia.com>,
	Jonathan Corbet <corbet@lwn.net>, Ingo Molnar <mingo@redhat.com>,
	Randy Dunlap <rdunlap@infradead.org>
Subject: Re: [PATCH] doc: Update wake_up() & co. memory-barrier guarantees
Date: Mon, 25 Jun 2018 13:12:45 +0100	[thread overview]
Message-ID: <2779.1529928765@warthog.procyon.org.uk> (raw)
In-Reply-To: <20180625095031.GX2494@hirez.programming.kicks-ass.net>

Peter Zijlstra <peterz@infradead.org> wrote:

> So yes, I suppose we're entirely suck with the full memory barrier
> semantics like that. But I still find it easier to think of it like a
> RELEASE that pairs with the ACQUIRE of waking up, such that the task
> is guaranteed to observe it's own wake condition.
> 
> And maybe that is the thing I'm missing here. These comments only state
> that it does in fact imply a full memory barrier, but do not explain
> why, should it?

I think because RELEASE and ACQUIRE concepts didn't really exist in Linux at
the time I wrote the doc, so the choices were read/readdep, write or full.

Since this document defines the *minimum* you can expect rather than what the
kernel actually gives you, I think it probably makes sense to switch to
RELEASE and ACQUIRE here.

David

  parent reply	other threads:[~2018-06-25 12:12 UTC|newest]

Thread overview: 38+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-06-25  9:17 [PATCH] doc: Update wake_up() & co. memory-barrier guarantees Andrea Parri
2018-06-25  9:17 ` Andrea Parri
2018-06-25  9:50 ` Peter Zijlstra
2018-06-25  9:50   ` Peter Zijlstra
2018-06-25 10:56   ` Andrea Parri
2018-06-25 10:56     ` Andrea Parri
2018-06-25 12:31     ` Peter Zijlstra
2018-06-25 12:31       ` Peter Zijlstra
2018-06-25 13:16       ` Andrea Parri
2018-06-25 13:16         ` Andrea Parri
2018-06-25 14:18         ` Peter Zijlstra
2018-06-25 14:18           ` Peter Zijlstra
2018-06-25 14:56           ` Andrea Parri
2018-06-25 14:56             ` Andrea Parri
2018-06-25 15:44             ` Daniel Lustig
2018-06-25 15:44               ` Daniel Lustig
2018-06-25 16:38               ` Peter Zijlstra
2018-06-25 16:38                 ` Peter Zijlstra
2018-06-25 16:37             ` Peter Zijlstra
2018-06-25 16:37               ` Peter Zijlstra
2018-06-26 10:09               ` Andrea Parri
2018-06-26 10:09                 ` Andrea Parri
2018-06-26 15:30                 ` Peter Zijlstra
2018-06-26 15:30                   ` Peter Zijlstra
2018-06-27 14:15       ` Andrea Parri
2018-06-27 14:15         ` Andrea Parri
2018-06-25 12:12   ` David Howells [this message]
2018-06-25 12:12     ` David Howells
2018-06-25 12:28     ` Andrea Parri
2018-06-25 12:28       ` Andrea Parri
2018-06-25 13:00       ` Peter Zijlstra
2018-06-25 13:00         ` Peter Zijlstra
2018-06-25 16:56 ` Alan Stern
2018-06-25 16:56   ` Alan Stern
2018-06-26 10:11   ` Andrea Parri
2018-06-26 10:11     ` Andrea Parri
2018-06-26 13:49     ` Alan Stern
2018-06-26 13:49       ` Alan Stern

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