From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-10.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 181BDC43219 for ; Fri, 3 May 2019 15:36:48 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 980722075E for ; Fri, 3 May 2019 15:36:47 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 980722075E Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=kernel.crashing.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from lists.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 44wbpP5k6nzDqrW for ; Sat, 4 May 2019 01:36:45 +1000 (AEST) Authentication-Results: lists.ozlabs.org; spf=permerror (mailfrom) smtp.mailfrom=kernel.crashing.org (client-ip=63.228.1.57; helo=gate.crashing.org; envelope-from=segher@kernel.crashing.org; receiver=) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=kernel.crashing.org Received: from gate.crashing.org (gate.crashing.org [63.228.1.57]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 44wbmn6jmNzDqVQ for ; Sat, 4 May 2019 01:35:21 +1000 (AEST) Received: from gate.crashing.org (localhost.localdomain [127.0.0.1]) by gate.crashing.org (8.14.1/8.14.1) with ESMTP id x43FZBDB027504; Fri, 3 May 2019 10:35:11 -0500 Received: (from segher@localhost) by gate.crashing.org (8.14.1/8.14.1/Submit) id x43FZAMT027503; Fri, 3 May 2019 10:35:10 -0500 X-Authentication-Warning: gate.crashing.org: segher set sender to segher@kernel.crashing.org using -f Date: Fri, 3 May 2019 10:35:10 -0500 From: Segher Boessenkool To: Stewart Smith Subject: Re: [PATCH kernel] prom_init: Fetch flatten device tree from the system firmware Message-ID: <20190503153510.GO8599@gate.crashing.org> References: <20190501034221.18437-1-aik@ozlabs.ru> <20190502042702.GH13618@umbus.fritz.box> <87bm0ktn1q.fsf@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87bm0ktn1q.fsf@linux.vnet.ibm.com> User-Agent: Mutt/1.4.2.3i X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Alexey Kardashevskiy , linuxppc-dev@lists.ozlabs.org, Suraj Jitindar Singh , David Gibson Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Fri, May 03, 2019 at 10:10:57AM +1000, Stewart Smith wrote: > David Gibson writes: > > On Wed, May 01, 2019 at 01:42:21PM +1000, Alexey Kardashevskiy wrote: > >> At the moment, on 256CPU + 256 PCI devices guest, it takes the guest > >> about 8.5sec to fetch the entire device tree via the client interface > >> as the DT is traversed twice - for strings blob and for struct blob. > >> Also, "getprop" is quite slow too as SLOF stores properties in a linked > >> list. > >> > >> However, since [1] SLOF builds flattened device tree (FDT) for another > >> purpose. [2] adds a new "fdt-fetch" client interface for the OS to fetch > >> the FDT. > >> > >> This tries the new method; if not supported, this falls back to > >> the old method. > >> > >> There is a change in the FDT layout - the old method produced > >> (reserved map, strings, structs), the new one receives only strings and > >> structs from the firmware and adds the final reserved map to the end, > >> so it is (fw reserved map, strings, structs, reserved map). > >> This still produces the same unflattened device tree. > >> > >> This merges the reserved map from the firmware into the kernel's reserved > >> map. At the moment SLOF generates an empty reserved map so this does not > >> change the existing behaviour in regard of reservations. > >> > >> This supports only v17 onward as only that version provides dt_struct_size > >> which works as "fdt-fetch" only produces v17 blobs. > >> > >> If "fdt-fetch" is not available, the old method of fetching the DT is used. > >> > >> [1] https://git.qemu.org/?p=SLOF.git;a=commitdiff;h=e6fc84652c9c00 > >> [2] https://git.qemu.org/?p=SLOF.git;a=commit;h=ecda95906930b80 > >> > >> Signed-off-by: Alexey Kardashevskiy > > > > Hrm. I've gotta say I'm not terribly convinced that it's worth adding > > a new interface we'll need to maintain to save 8s on a somewhat > > contrived testcase. > > 256CPUs aren't that many anymore though. Although I guess that many PCI > devices is still a little uncommon. > > A 4 socket POWER8 or POWER9 can easily be that large, and a small test > kernel/userspace will boot in ~2.5-4 seconds. So it's possible that > the device tree fetch could be surprisingly non-trivial percentage of boot > time at least on some machines. All client interface calls are really heavy, and you need to do a lot of them if you have a big device tree. This takes time, even if the linked list stuff does not kill you :-) Segher