From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 97BD46088F for ; Wed, 13 Nov 2024 12:56:29 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1731502592; cv=none; b=ovhIFVy9LS/sIWzF9Zzs/NvEhFb8m9rI3KhklzK0/0rFk2ddAt9v712DkffDhNsPWj7pUeydzpoWTO2vmk7wQPkjfZb9aVr6zXoulpKYpEEcDltrkthAX/sULrKi8Ub6d+OtpvOkKv4mKn/aP7HanspDYxOglPRfKvcFR71+RIY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1731502592; c=relaxed/simple; bh=5W3XVCZi0AeqVKhPv2nTx1LkaCHpXgsHjbigdUIU3Pk=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=LGyZPVMFrySpEVDGLxGHYVN8j8MSU+5nZ2hEMv60jZWHGKWgQC86UB8/31H0PP/n5PTIwr0jKa/fZzMic+Wsk3jS3PMxtgtP9UUgNiW8OSFC0n+quvJz+QhK/pei7I5qTsaq2keRymYoG4yDz9pRhduN4dBP0r+I8OFSjZACGgE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com 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 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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 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