From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932656AbeCIXDu (ORCPT ); Fri, 9 Mar 2018 18:03:50 -0500 Received: from mail-oi0-f67.google.com ([209.85.218.67]:34944 "EHLO mail-oi0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932373AbeCIXDs (ORCPT ); Fri, 9 Mar 2018 18:03:48 -0500 X-Google-Smtp-Source: AG47ELsd4Hps2NYmCyJkIi6vPn7ez6X4CX7hfecs2zjCvVUnJHVKwOk2ldtHJxKtEWzNIMzXSiN60A== Date: Fri, 9 Mar 2018 17:03:46 -0600 From: Rob Herring To: frowand.list@gmail.com Cc: cpandya@codeaurora.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v5 1/3] of: cache phandle nodes to reduce cost of of_find_node_by_phandle() Message-ID: <20180309230346.7mphnvsdxugpmtmc@rob-hp-laptop> References: <1520208889-3908-1-git-send-email-frowand.list@gmail.com> <1520208889-3908-2-git-send-email-frowand.list@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1520208889-3908-2-git-send-email-frowand.list@gmail.com> User-Agent: NeoMutt/20170609 (1.8.3) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Mar 04, 2018 at 04:14:47PM -0800, frowand.list@gmail.com wrote: > From: Frank Rowand > > Create a cache of the nodes that contain a phandle property. Use this > cache to find the node for a given phandle value instead of scanning > the devicetree to find the node. If the phandle value is not found > in the cache, of_find_node_by_phandle() will fall back to the tree > scan algorithm. > > The cache is initialized in of_core_init(). > > The cache is freed via a late_initcall_sync() if modules are not > enabled. > > If the devicetree is created by the dtc compiler, with all phandle > property values auto generated, then the size required by the cache > could be 4 * (1 + number of phandles) bytes. This results in an O(1) > node lookup cost for a given phandle value. Due to a concern that the > phandle property values might not be consistent with what is generated > by the dtc compiler, a mask has been added to the cache lookup algorithm. > To maintain the O(1) node lookup cost, the size of the cache has been > increased by rounding the number of entries up to the next power of > two. > > The overhead of finding the devicetree node containing a given phandle > value has been noted by several people in the recent past, in some cases > with a patch to add a hashed index of devicetree nodes, based on the > phandle value of the node. One concern with this approach is the extra > space added to each node. This patch takes advantage of the phandle > property values auto generated by the dtc compiler, which begin with > one and monotonically increase by one, resulting in a range of 1..n > for n phandle values. This implementation should also provide a good > reduction of overhead for any range of phandle values that are mostly > in a monotonic range. > > Performance measurements by Chintan Pandya > of several implementations of patches that are similar to this one > suggest an expected reduction of boot time by ~400ms for his test > system. If the cache size was decreased to 64 entries, the boot > time was reduced by ~340 ms. The measurements were on a 4.9.73 kernel > for arch/arm64/boot/dts/qcom/sda670-mtp.dts, contains 2371 nodes and > 814 phandle values. > > Reported-by: Chintan Pandya > Signed-off-by: Frank Rowand > --- I've applied this one, but not the others. Rob