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 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 1348ED41C3E for ; Wed, 13 Nov 2024 12:58:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: Content-Type:In-Reply-To:From:References:Cc:To:Subject:MIME-Version:Date: Message-ID:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=paG34W9RuUFqjynCcqmF9vylDQ8hE8NgKGEWL4OoefM=; b=vNaPU+onuwHvgs+Bj632aH1CfG P8upVyx3PupBWA5BOFIJBg24atqPAvUPiYUzJXwlNld2j7XEA4RQ1Z2Rrgd/WUKd3eHw9Q57BVx2p xTbTZ5IAPrVOs83+X4AhlXfEVfpX7kr+Oc1IepSH3lSF4sevBjq/lnSiTjd92bseQtbFCu+Sur+1z GZRPMzPR5j0OJjhjQ9EBuJD6Ek+hRBOOxnTKvdghdd+1W8PLnS0dYnF0CiOf/ygefJudqG6uVqU1f Ns7maeQa9yFRiMhS7HKalSK5LviYd2oQsVJ5LnB7PIlQDIAHge7LkhqEJ2gqEy4qE/e5ktKGWa/G5 eqKFF6mg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98 #2 (Red Hat Linux)) id 1tBCwy-00000006qYQ-2t82; Wed, 13 Nov 2024 12:58:24 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.98 #2 (Red Hat Linux)) id 1tBCvA-00000006qF7-0Wun for linux-arm-kernel@lists.infradead.org; Wed, 13 Nov 2024 12:56:34 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 738261655; Wed, 13 Nov 2024 04:56:58 -0800 (PST) Received: from [10.1.38.177] (XHFQ2J9959.cambridge.arm.com [10.1.38.177]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id D103C3F66E; Wed, 13 Nov 2024 04:56:25 -0800 (PST) Message-ID: Date: Wed, 13 Nov 2024 12:56:24 +0000 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH v1 00/57] Boot-time page size selection for arm64 Content-Language: en-GB To: Petr Tesarik Cc: Andrew Morton , Anshuman Khandual , Ard Biesheuvel , Catalin Marinas , David Hildenbrand , Greg Marsden , Ivan Ivanov , Kalesh Singh , Marc Zyngier , Mark Rutland , Matthias Brugger , Miroslav Benes , Will Deacon , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <20241014105514.3206191-1-ryan.roberts@arm.com> <20241017142752.17f2c816@mordecai.tesarici.cz> <20241111131442.51738a30@mordecai.tesarici.cz> <046ce0ae-b4d5-4dbd-ad9d-eb8de1bba1b8@arm.com> <20241112104544.574dd733@mordecai.tesarici.cz> <5a041e51-a43b-4878-ab68-4757d3141889@arm.com> <20241112115039.41993e4b@mordecai.tesarici.cz> <20241113134038.5843ab73@mordecai.tesarici.cz> From: Ryan Roberts In-Reply-To: <20241113134038.5843ab73@mordecai.tesarici.cz> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20241113_045632_287179_BD605386 X-CRM114-Status: GOOD ( 25.15 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 13/11/2024 12:40, Petr Tesarik wrote: > On Tue, 12 Nov 2024 11:50:39 +0100 > Petr Tesarik wrote: > >> On Tue, 12 Nov 2024 10:19:34 +0000 >> Ryan Roberts wrote: >> >>> On 12/11/2024 09:45, Petr Tesarik wrote: >>>> On Mon, 11 Nov 2024 12:25:35 +0000 >>>> Ryan Roberts wrote: >>>> >>>>> Hi Petr, >>>>> >>>>> On 11/11/2024 12:14, Petr Tesarik wrote: >>>>>> Hi Ryan, >>>>>> >>>>>> On Thu, 17 Oct 2024 13:32:43 +0100 >>>>>> Ryan Roberts wrote: >>>>> [...] >>>>>> Third, a few micro-benchmarks saw a significant regression. >>>>>> >>>>>> Most notably, getenv and getenvT2 tests from libMicro were 18% and 20% >>>>>> slower with variable page size. I don't know why, but I'm looking into >>>>>> it. The system() library call was also about 18% slower, but that might >>>>>> be related. >>>>> >>>>> OK, ouch. I think there are some things we can try to optimize the >>>>> implementation further. But I'll wait for your analysis before digging myself. >>>> >>>> This turned out to be a false positive. The way this microbenchmark was >>>> invoked did not get enough samples, so it was mostly dependent on >>>> whether caches were hot or cold, and the timing on this specific system >>>> with the specific sequence of bencnmarks in the suite happens to favour >>>> my baseline kernel. >>>> >>>> After increasing the batch count, I'm getting pretty much the same >>>> performance for 6.11 vanilla and patched kernels: >>>> >>>> prc thr usecs/call samples errors cnt/samp >>>> getenv (baseline) 1 1 0.14975 99 0 100000 >>>> getenv (patched) 1 1 0.14981 92 0 100000 >>> >>> Oh that's good news! Does this account for all 3 of the above tests (getenv, >>> getenvT2 and system())? >> >> It does for getenvT2 (a variant of the test with 2 threads), but not >> for system. Thanks for asking, I forgot about that one. >> >> I'm getting substantial difference there (+29% on average over 100 runs): >> >> prc thr usecs/call samples errors cnt/samp command >> system (baseline) 1 1 6937.18016 102 0 100 A=$$ >> system (patched) 1 1 8959.48032 102 0 100 A=$$ >> >> So, yeah, this should in fact be my priority #1. > > Further testing reveals the workload is bimodal, that is to say the > distribution of results has two peaks. The first peak around 3.2 ms > covers 30% runs, the second peak around 15.7 ms covers 11%. Two per > cent are faster than the fast peak, 5% are slower than slow peak, the > rest is distributed almost evenly between them. FWIW, One source of bimodality I've seen on Ampere systems with 2 NUMA nodes is placement of the kernel image vs placement of the running thread. If they are remote from eachother, you'll see a slowdown. I've hacked this source away in the past by effectively using only a single NUMA node (with the help of 'maxcpus' and 'mem' kernel cmdline options). > > 100 samples were not sufficient to see this distribution, and it was > mere bad luck that only the patched kernel originally reported bad > results. I can now see bad results even with the unpatched kernel. > > In short, I don't think there is a difference in system() performance. > > I will still have a look at dup() and VMA performance, but so far it > all looks good to me. Good job! ;-) Thanks for digging into all this! > > I will also try running a more complete set of benchmarks during next > week. That's SUSE Hack Week, and I want to make a PoC for the MM > changes I proposed at LPC24, so I won't need this Ampere system for > interactive use. > > Petr T