Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754398AbdCTLwX (ORCPT ); Mon, 20 Mar 2017 07:52:23 -0400 Received: from foss.arm.com ([217.140.101.70]:37182 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754217AbdCTLwM (ORCPT ); Mon, 20 Mar 2017 07:52:12 -0400 Date: Mon, 20 Mar 2017 11:52:15 +0000 From: Will Deacon To: Ding Tianhong Cc: Robin Murphy , Catalin Marinas , linux-arm-kernel@lists.infradead.org, "linux-kernel@vger.kernel.org" , alexander.duyck@gmail.com, Mao Wenan Subject: Re: [PATCH] arm64: enable ARCH_WANT_RELAX_ORDER for aarch64 Message-ID: <20170320115214.GG17263@arm.com> References: <35233df0-3406-e66f-d9d2-bf7ed7814386@huawei.com> <5bcff420-2ba7-7f64-9c52-41a5c60e9c31@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5bcff420-2ba7-7f64-9c52-41a5c60e9c31@huawei.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1578 Lines: 37 On Tue, Mar 14, 2017 at 10:06:48PM +0800, Ding Tianhong wrote: > On 2017/3/13 21:31, Robin Murphy wrote: > > On 13/03/17 12:03, Ding Tianhong wrote: > >> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > >> index 8c7c244..36249a3 100644 > >> --- a/arch/arm64/Kconfig > >> +++ b/arch/arm64/Kconfig > >> @@ -115,6 +115,7 @@ config ARM64 > >> select SPARSE_IRQ > >> select SYSCTL_EXCEPTION_TRACE > >> select THREAD_INFO_IN_TASK > >> + select ARCH_WANT_RELAX_ORDER > > > > I'd say the first order of business is to rename this config option to > > IXBGE_82599_WANT_RELAXED_ORDER so that it's not entirely misleading and > > not only for 82599, including 82598, 82576.... > > > ambiguous. At first glance it looks far more like something scary to do > > with memory barriers than a network driver option. Howcome this isn't > > just in drivers/net/intel/Kconfig as a "default y if SPARC" bool anyway? > > didn't see any essential differences, and I still need to get some Acked by arm maintainer. > > > > > Yes, more memory barriers always affect the performance especially for > some architecture not just like sparc, any optimization should be taken seriously > especially for aarch64. If this is a legitimate optimisation to apply (which nobody seems to be sure about), then I'd *much* rather it was handled entirely in the driver and predicated on CONFIG_ARM64. I can't select ARCH_WANT_RELAX_ORDER without some notion of what on Earth that means, and whether or not other drivers can also use that to infer some property about the arm64 ordering model. Will