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

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Message-ID: <CA+55aFy3k_NouhizkAkiZkuTYTqEKQZCnz8yOzrSH8o4+vjKUw@mail.gmail.com>
Date:	Tue, 22 Sep 2015 12:28:45 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Tejun Heo <tj@...nel.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

On Tue, Sep 22, 2015 at 11:53 AM, Tejun Heo <tj@...nel.org> wrote:
>
> 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.

Both acquire and smp_rmb() are equally free on x86.

It appears that we don't do the X86_PPRO_FENCE bug handling for
acquire, but I guess we should.

Or possibly we should start deprecating the insane X86_PPRO_FENCE
entirely. It's very costly, for dubious advantages.

                  Linus
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