From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759095Ab0KPBrz (ORCPT ); Mon, 15 Nov 2010 20:47:55 -0500 Received: from wolverine01.qualcomm.com ([199.106.114.254]:24530 "EHLO wolverine01.qualcomm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755442Ab0KPBry (ORCPT ); Mon, 15 Nov 2010 20:47:54 -0500 X-IronPort-AV: E=McAfee;i="5400,1158,6168"; a="62976885" Message-ID: <4CE1E2CA.30001@codeaurora.org> Date: Mon, 15 Nov 2010 17:47:54 -0800 From: Stepan Moskovchenko User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.2.11) Gecko/20101013 Thunderbird/3.1.5 MIME-Version: 1.0 To: Daniel Walker CC: davidb@codeaurora.org, bryanh@codeaurora.org, linux-arm-msm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 09/14] msm: iommu: Kconfig option for cacheable page tables References: <1289619000-13167-1-git-send-email-stepanm@codeaurora.org> <1289619000-13167-10-git-send-email-stepanm@codeaurora.org> <1289765858.24270.240.camel@m0nster> <8bd62d321211c93af883cd2ad404e802.squirrel@www.codeaurora.org> <1289845236.4050.25.camel@c-dwalke-linux.qualcomm.com> In-Reply-To: <1289845236.4050.25.camel@c-dwalke-linux.qualcomm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/15/2010 10:20 AM, Daniel Walker wrote: > On Sun, 2010-11-14 at 18:56 -0800, Stepan Moskovchenko wrote: >>> On Fri, 2010-11-12 at 19:29 -0800, Stepan Moskovchenko wrote: >>>> +config IOMMU_PGTABLES_L2 >>>> + depends on ARCH_MSM8X60 >>>> + depends on MMU >>>> + depends on CPU_DCACHE_DISABLE=n >>>> + depends on SMP >>>> + bool "Cacheable IOMMU page tables" >>>> + default y >>>> + help >>>> + Allows the IOMMU page tables to be brought into the L2 cache. This >>>> + improves the TLB miss latency at the expense of potential pollution >>>> + of the L2 cache. This option has been shown to improve multimedia >>>> + performance in some cases. >>>> + >>>> + If unsure, say Y here. >>> Why would someone want this off? >>> >>> The other thing is that you usually want this included with the code >>> that uses the option. >> The code that uses it had gone in during a previous patch series, but I >> didn't want to meddle in the Kconfig just yet, especially since the option >> only improves performance and does not add new functionality at a high >> level. This patch should be the last of what is needed for this feature. >> >> You would want to turn this off if you wanted more deterministic behavior >> from the multimedia subsystem, such as when trying to run benchmarks for >> the worst-case behavior in terms of memory latency and TLB misses. You >> might also want to turn it off if you are debugging memory problems that >> you suspect might be related to the cache maintenance code, in which case >> turning this off would give an idea as to whether that is the problem. >> Similarly, this needs to be off (and will be, due to the dependencies) if >> certain required things (like the Dcache, MMU, etc) have been disabled. >> Finally, if you are doing things with the MMSS that you know will not >> result in many TLB misses, (or if you know that you can tolerate high miss >> latency) you may as well turn this off to avoid the (small) bit of cache >> pollution. > It sounds like you don't really want it off unless your a developer (or > you turn one of the dependencies) .. I think this might be better as a > hidden option just cause of the developer centric nature of it. > > Daniel Alright. Fixed in v2. Steve --- Sent by an employee of the Qualcomm Innovation Center, Inc. The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.