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=-2.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no 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 6F0F1C43603 for ; Tue, 10 Dec 2019 12:46:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 379AB2073B for ; Tue, 10 Dec 2019 12:46:19 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="AGaM03rJ" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727211AbfLJMqS (ORCPT ); Tue, 10 Dec 2019 07:46:18 -0500 Received: from mail-pg1-f195.google.com ([209.85.215.195]:37250 "EHLO mail-pg1-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727131AbfLJMqS (ORCPT ); Tue, 10 Dec 2019 07:46:18 -0500 Received: by mail-pg1-f195.google.com with SMTP id q127so8866698pga.4 for ; Tue, 10 Dec 2019 04:46:18 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=subject:from:to:cc:references:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=0RJ9gOA6O4Gv2PmI1ZeznCe4B5gXlbgOZ+kRt1JJlWA=; b=AGaM03rJG2HvZgtroua9DONqlW0TCJEGAn0tgzJ1p3K/e6c66dn+mLz1bNWOpnlsNi ield6vWnLrPrMHs6r6xtSTkFNCe8/FdKZzPIL9R4f7upA8GkkhcZ8DqvVb/zE8fkJXRM tXQt97dpECuSIZW1sPWumefp9f4PrPDw/qfYyJcPyLCPprlrP5EfWl2/uQH0luALQlrf J7JLJoqTZmbmwff339HV5oS0dMv3I+GVIWfglx/1yn7H+UMUCsumcSY5FpXbD2wkQeN2 4r8/5j4VbHT0SPjA4aFsZxhp3v/2dE1Wq3jyoeKmwSY2EGKRDaW/FjIlFqJve6UEfFul gKDw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:from:to:cc:references:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=0RJ9gOA6O4Gv2PmI1ZeznCe4B5gXlbgOZ+kRt1JJlWA=; b=FX28eg9E2RHaKv7gAtJvMO2bIBjv5QoEr9OYixmGT3Mop/V8JqjwAoHl9mQI3aDEu6 9I6bT9Oh8acSb84gwB/LohxG0PUFx+T7EUy/Khlj0S7IZP6pduHTGu783tJv78eEAt1o MR0eNeQY7nyP6n+ccfo5cXtNjjj+H5KBsYmvzd2NG5X6eyc0j70E8/OqI2IIlO1TfkBs tOy6ceKUvpgHCgCj03bY+FUTKd98SjiVd3wCJ65SqhOf74yW9JOqQ8iD7+s1Z1/Bb8F0 LFNnIJVyOkLEA5s2kufdFVTAzTF7kX8VEYm3M524G2PeSKwzMFLttIcidvDsDJYeVSzb RD8A== X-Gm-Message-State: APjAAAWlOTCCw39ZbX/RhzozREThGGYlzadsfgwn+2d0LRbzQttKPeLU fS+pKCie+F0TVvOXSXy8b90= X-Google-Smtp-Source: APXvYqyWc0ec2Q8xLT/YvvzRe07Ppkdx7eIhxEjhKuJDc2LYUl4PMRFYdR2r0ioGM2RVNhMyvu8tRg== X-Received: by 2002:a63:604:: with SMTP id 4mr25213550pgg.406.1575981977596; Tue, 10 Dec 2019 04:46:17 -0800 (PST) Received: from [10.231.110.95] ([125.29.25.186]) by smtp.gmail.com with ESMTPSA id s18sm3315511pfh.47.2019.12.10.04.46.14 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 10 Dec 2019 04:46:17 -0800 (PST) Subject: Re: [RFC] Efficiency of the phandle_cache on ppc64/SLOF From: Frank Rowand To: Rob Herring , Sebastian Andrzej Siewior Cc: Michael Ellerman , devicetree@vger.kernel.org, linuxppc-dev , Benjamin Herrenschmidt , Paul Mackerras , Thomas Gleixner References: <20191129151056.o5c44lm5lb4wsr4r@linutronix.de> <87tv6idp37.fsf@mpe.ellerman.id.au> <67e1da87-7f5a-3972-bc16-28bae2350c12@gmail.com> <20191205163538.mzunfrpox7jbrssl@linutronix.de> <084ed924-eaed-5232-a9f6-fe60128fe11a@gmail.com> <20191209133531.ykkknqmeeb36rv7l@linutronix.de> Message-ID: <174936b9-bd2c-8850-aa8f-f4c605b0f1d5@gmail.com> Date: Tue, 10 Dec 2019 06:46:08 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.9.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: devicetree-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: devicetree@vger.kernel.org On 12/10/19 2:17 AM, Frank Rowand wrote: > On 12/9/19 7:51 PM, Rob Herring wrote: >> On Mon, Dec 9, 2019 at 7:35 AM Sebastian Andrzej Siewior >> wrote: >>> >>> On 2019-12-05 20:01:41 [-0600], Frank Rowand wrote: >>>> Is there a memory usage issue for the systems that led to this thread? >>> >>> No, no memory issue led to this thread. I was just testing my patch and >>> I assumed that I did something wrong in the counting/lock drop/lock >>> acquire/allocate path because the array was hardly used. So I started to >>> look deeper… >>> Once I figured out everything was fine, I was curious if everyone is >>> aware of the different phandle creation by dtc vs POWER. And I posted >>> the mail in the thread. >>> Once you confirmed that everything is "known / not an issue" I was ready >>> to take off [0]. >>> >>> Later more replies came in such as one mail [1] from Rob describing the >>> original reason with 814 phandles. _Here_ I was just surprised that 1024 >>> were used over 64 entries for a benefit of 60ms. I understand that this >>> is low concern for you because that memory is released if modules are >>> not enabled. I usually see that module support is left enabled. >>> >>> However, Rob suggested / asked about the fixed size array (this is how I >>> understood it): >>> |And yes, as mentioned earlier I don't like the complexity. I didn't >>> |from the start and I'm I'm still of the opinion we should have a >>> |fixed or 1 time sized true cache (i.e. smaller than total # of >>> |phandles). That would solve the RT memory allocation and locking issue >>> |too. >>> >>> so I attempted to ask if we should have the fixed size array maybe >>> with the hash_32() instead the mask. This would make my other patch >>> obsolete because the fixed size array should not have a RT issue. The >>> hash_32() part here would address the POWER issue where the cache is >>> currently not used efficiently. >>> >>> If you want instead to keep things as-is then this is okay from my side. >>> If you want to keep this cache off on POWER then I could contribute a >>> patch doing so. >> >> It turns out there's actually a bug in the current implementation. If >> we have multiple phandles with the same mask, then we leak node >> references if we miss in the cache and re-assign the cache entry. > > Aaargh. Patch sent. > >> Easily fixed I suppose, but holding a ref count for a cached entry >> seems wrong. That means we never have a ref count of 0 on every node >> with a phandle. > > It will go to zero when the cache is freed. > > My memory is that we free the cache as part of removing an overlay. I'll > verify whether my memory is correct. And I'll look at non-overlay use of dynamic devicetree too. -Frank > > -Frank > > >> >> I've done some more experiments with the performance. I've come to the >> conclusion that just measuring boot time is not a good way at least if >> the time is not a significant percentage of the total. I couldn't get >> any measurable data. I'm using a RK3399 Rock960 board. It has 190 >> phandles. I get about 1500 calls to of_find_node_by_phandle() during >> boot. Note that about the first 300 are before we have any timekeeping >> (the prior measurements also would not account for this). Those calls >> have no cache in the current implementation and are cached in my >> implementation. >> >> no cache: 20124 us >> current cache: 819 us >> >> new cache (64 entry): 4342 us >> new cache (128 entry): 2875 us >> new cache (256 entry): 1235 us >> >> To get some idea on the time spent before timekeeping is up, if we >> take the avg miss time is ~17us (20124/1200), then we're spending >> about ~5ms on lookups before the cache is enabled. I'd estimate the >> new cache takes ~400us before timekeeping is up as there's 11 misses >> early. >> >> >From these numbers, it seems the miss rate has a significant impact on >> performance for the different sizes. But taken from the original 20+ >> ms, they all look like good improvement. >> >> Rob >> > >