From: Peter Zijlstra <peterz@infradead.org>
To: Chris Metcalf <cmetcalf@mellanox.com>
Cc: linux-kernel@vger.kernel.org, torvalds@linux-foundation.org,
manfred@colorfullife.com, dave@stgolabs.net,
paulmck@linux.vnet.ibm.com, will.deacon@arm.com,
boqun.feng@gmail.com, Waiman.Long@hpe.com, tj@kernel.org,
pablo@netfilter.org, kaber@trash.net, davem@davemloft.net,
oleg@redhat.com, netfilter-devel@vger.kernel.org,
sasha.levin@oracle.com, hofrat@osadl.org, rth@twiddle.net,
vgupta@synopsys.com, linux@armlinux.org.uk, realmz6@gmail.com,
rkuo@codeaurora.org, tony.luck@intel.com, james.hogan@imgtec.com,
ralf@linux-mips.org, dhowells@redhat.com, jejb@parisc-linux.org,
mpe@ellerman.id.au, schwidefsky@de.ibm.com,
ysato@users.sourceforge.jp, chris@zankel.net
Subject: Re: [PATCH -v2 4/6] locking, arch: Update spin_unlock_wait()
Date: Mon, 30 May 2016 11:25:20 +0200 [thread overview]
Message-ID: <20160530092520.GQ3192@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <903f2076-9e24-afb7-0b17-e41457854907@mellanox.com>
On Fri, May 27, 2016 at 03:34:13PM -0400, Chris Metcalf wrote:
> >Does TILE never speculate reads? Because in that case the control
> >dependency already provides a full load->load,store barrier and you'd
> >want smp_acquire__after_ctrl_dep() to be a barrier() instead of
> >smp_rmb().
>
> Yes, that's a good point. I didn't look at the definition of smp_acquire__after_ctrl_dep(),
> but it certainly sounds like that's exactly a compiler barrier for tile. There is no load
> speculation performed. The only out-of-order stuff that happens is in the memory
> subsystem: stores will become visible in arbitrary order, and loads will arrive in
> arbitrary order, but as soon as the result of a load is used in any other kind of
> instruction, the instruction issue will halt until the pending load(s) for the instruction
> operands are available.
OK; for now I'll just put in barrier() and a big comment, I'll look at
making smp_acquire__after_ctrl_dep() a proper (per arch) barrier later.
There's a little header head-ache involved.
next prev parent reply other threads:[~2016-05-30 9:26 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-05-26 14:19 [PATCH -v2 0/6] spin_unlock_wait borkage Peter Zijlstra
2016-05-26 14:19 ` [PATCH -v2 1/6] locking: Replace smp_cond_acquire with smp_cond_load_acquire Peter Zijlstra
2016-05-26 14:19 ` [PATCH -v2 2/6] locking: Introduce cmpwait() Peter Zijlstra
2016-05-26 14:19 ` [PATCH -v2 3/6] locking: Introduce smp_acquire__after_ctrl_dep Peter Zijlstra
2016-05-26 14:19 ` [PATCH -v2 4/6] locking, arch: Update spin_unlock_wait() Peter Zijlstra
2016-05-26 21:10 ` Chris Metcalf
2016-05-27 9:05 ` Peter Zijlstra
2016-05-27 19:34 ` Chris Metcalf
2016-05-30 9:25 ` Peter Zijlstra [this message]
2016-05-27 6:46 ` Martin Schwidefsky
2016-05-27 9:02 ` Peter Zijlstra
2016-05-26 14:19 ` [PATCH -v2 5/6] locking: Update spin_unlock_wait users Peter Zijlstra
2016-05-26 14:19 ` [PATCH -v2 6/6] locking,netfilter: Fix nf_conntrack_lock() Peter Zijlstra
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