From: "Michael S. Tsirkin" <mst@redhat•com>
To: Peter Zijlstra <peterz@infradead•org>
Cc: "Paul E. McKenney" <paulmck@linux•vnet.ibm.com>,
linux-kernel@vger•kernel.org, mingo@kernel•org,
jiangshanlai@gmail•com, dipankar@in•ibm.com,
akpm@linux-foundation•org, mathieu.desnoyers@efficios•com,
josh@joshtriplett•org, tglx@linutronix•de, rostedt@goodmis•org,
dhowells@redhat•com, edumazet@google•com, fweisbec@gmail•com,
oleg@redhat•com, Jason Wang <jasowang@redhat•com>,
kvm@vger•kernel.org, virtualization@lists•linux-foundation.org,
netdev@vger•kernel.org
Subject: Re: [PATCH tip/core/rcu 21/21] drivers/vhost: Remove now-redundant read_barrier_depends()
Date: Tue, 5 Dec 2017 23:42:44 +0200 [thread overview]
Message-ID: <20171205232516-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <20171205211735.GT3165@worktop.lehotels.local>
On Tue, Dec 05, 2017 at 10:17:35PM +0100, Peter Zijlstra wrote:
> On Tue, Dec 05, 2017 at 10:28:38PM +0200, Michael S. Tsirkin wrote:
> > On Tue, Dec 05, 2017 at 08:57:52PM +0100, Peter Zijlstra wrote:
> > > On Tue, Dec 05, 2017 at 09:51:48PM +0200, Michael S. Tsirkin wrote:
> > > > > > WRITE_ONCE(obj->val, 1);
> > > > > > smp_wmb();
> > > > > > WRITE_ONCE(*foo, obj);
> > > > >
> > > > > I believe Peter was instead suggesting:
> > > > >
> > > > > WRITE_ONCE(obj->val, 1);
> > > > > smp_store_release(foo, obj);
> > > >
> > > > Isn't that more expensive though?
> > >
> > > Depends on the architecture. The only architecture where it is more
> > > expensive and people actually still care about is ARM I think.
> >
> > Right. Why should I use the more expensive smp_store_release then?
>
> Because it makes more sense. Memory ordering is hard enough, don't make
> it harder still if you don't have to.
I suspect I have to - ptr_ring is a very low level construct used by
netowrking on data path so making it a bit more complicated for
a bit of performance is probably justified.
--
MST
next prev parent reply other threads:[~2017-12-05 21:42 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20171201195053.GA23494@linux.vnet.ibm.com>
2017-12-01 19:50 ` [PATCH tip/core/rcu 03/21] drivers/net/ethernet/qlogic/qed: Fix __qed_spq_block() ordering Paul E. McKenney
2017-12-01 19:51 ` [PATCH tip/core/rcu 14/21] netfilter: Remove now-redundant smp_read_barrier_depends() Paul E. McKenney
2017-12-01 19:51 ` [PATCH tip/core/rcu 21/21] drivers/vhost: Remove now-redundant read_barrier_depends() Paul E. McKenney
2017-12-05 18:31 ` Michael S. Tsirkin
2017-12-05 18:39 ` Peter Zijlstra
2017-12-05 18:57 ` Michael S. Tsirkin
2017-12-05 19:17 ` Peter Zijlstra
2017-12-05 19:24 ` Michael S. Tsirkin
2017-12-05 19:33 ` Paul E. McKenney
2017-12-05 19:51 ` Michael S. Tsirkin
2017-12-05 19:57 ` Peter Zijlstra
2017-12-05 20:28 ` Michael S. Tsirkin
2017-12-05 21:17 ` Peter Zijlstra
2017-12-05 21:42 ` Michael S. Tsirkin [this message]
2017-12-05 20:08 ` Paul E. McKenney
2017-12-05 21:24 ` Michael S. Tsirkin
2017-12-05 21:36 ` Paul E. McKenney
2017-12-05 21:43 ` Michael S. Tsirkin
2017-12-05 22:02 ` Paul E. McKenney
2017-12-05 22:09 ` Peter Zijlstra
2017-12-05 21:57 ` Peter Zijlstra
2017-12-05 22:09 ` Michael S. Tsirkin
2017-12-05 23:39 ` Paul E. McKenney
2017-12-05 19:55 ` Peter Zijlstra
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