linux-kernel - Re: [PATCH v2] netlink: Replace rhash

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Message-ID: <20150922185357.GD17659@mtj.duckdns.org>
Date:	Tue, 22 Sep 2015 14:53:57 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Herbert Xu <herbert@...dor.apana.org.au>,
	David Miller <davem@...emloft.net>,
	Cong Wang <cwang@...pensource.com>, tom@...bertland.com,
	kafai@...com, kernel-team@...com,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Network Development <netdev@...r.kernel.org>,
	Jiří Pírko <jiri@...nulli.us>,
	Nicolas Dichtel <nicolas.dichtel@...nd.com>,
	Thomas Graf <tgraf@...g.ch>, Scott Feldman <sfeldma@...il.com>
Subject: Re: [PATCH v2] netlink: Replace rhash_portid with bound

Hello, Linus.

On Tue, Sep 22, 2015 at 11:42:33AM -0700, Linus Torvalds wrote:
...
> smp_rmb() should generally be about the same cost as an acquire. It
> can go either way.
> 
> So *if* the algorithm is amenable to smp_wmb()/smp_rmb() kind of
> barriers, that's actually quite possibly better than acquire/release.

I see.  The write path here is cold so the competition is between rmb
and acquire.  Unless some significant archs completely screwed it up,
acquire still seems like the better option.  It's essentially free on
x86 after all.

Thanks.

-- 
tejun
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