From: Will Deacon <will.deacon@arm.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Oleg Nesterov <oleg@redhat.com>,
Paul McKenney <paulmck@linux.vnet.ibm.com>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Michael Ellerman <mpe@ellerman.id.au>,
linux-kernel@vger.kernel.org, Nicholas Piggin <npiggin@gmail.com>,
Ingo Molnar <mingo@kernel.org>,
Alan Stern <stern@rowland.harvard.edu>
Subject: Re: Question on smp_mb__before_spinlock
Date: Tue, 6 Sep 2016 18:42:10 +0100 [thread overview]
Message-ID: <20160906174209.GB29382@arm.com> (raw)
In-Reply-To: <20160906111753.GA10121@twins.programming.kicks-ass.net>
On Tue, Sep 06, 2016 at 01:17:53PM +0200, Peter Zijlstra wrote:
> On Mon, Sep 05, 2016 at 11:10:22AM +0100, Will Deacon wrote:
>
> > > The second issue I wondered about is spinlock transitivity. All except
> > > powerpc have RCsc locks, and since Power already does a full mb, would
> > > it not make sense to put it _after_ the spin_lock(), which would provide
> > > the same guarantee, but also upgrades the section to RCsc.
> > >
> > > That would make all schedule() calls fully transitive against one
> > > another.
> >
> > It would also match the way in which the arm64 atomic_*_return ops
> > are implemented, since full barrier semantics are required there.
>
> Hmm, are you sure; the way I read arch/arm64/include/asm/atomic_ll_sc.h
> is that you do ll/sc-rel + mb.
Yes, all I meant was that we put the full barrier at the end, but the
two things are indeed different sequences.
Will
next prev parent reply other threads:[~2016-09-06 17:42 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-09-05 9:37 Question on smp_mb__before_spinlock Peter Zijlstra
2016-09-05 9:56 ` kbuild test robot
2016-09-05 10:19 ` Peter Zijlstra
2016-09-05 11:26 ` Fengguang Wu
2016-09-05 10:10 ` Will Deacon
2016-09-06 11:17 ` Peter Zijlstra
2016-09-06 17:42 ` Will Deacon [this message]
2016-09-05 10:37 ` Paul E. McKenney
2016-09-05 11:34 ` Peter Zijlstra
2016-09-05 13:57 ` Paul E. McKenney
2016-09-05 10:51 ` kbuild test robot
2016-09-07 12:17 ` Nicholas Piggin
2016-09-07 13:23 ` Peter Zijlstra
2016-09-07 13:51 ` Will Deacon
2016-09-12 2:35 ` Nicholas Piggin
2016-09-12 2:27 ` Nicholas Piggin
2016-09-12 12:54 ` Peter Zijlstra
2016-09-13 2:05 ` Nicholas Piggin
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