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 7F8F1D32D75 for ; Tue, 12 Nov 2024 10:31:49 +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=2JQNvIKvzwZQGEHrsZ3sSnuvOwvNsdWPbA2dI8+nQ2E=; b=AyFKn5W4TI3NETUfKDyfRdZrv8 l/cF5JwdP5YcBXKYdZ3ADWH0GHOIAC4jj8QJ6auW7g1TPNRsKxmsqVLI9M+e2VodBNuNU6frl0h1v zU+dSC1aHAu24ygzQM/he3AKIbT1EiJQwjkVHd7RBX4UhnUFLL5JNx7ZhCfK3dhTN66ydV7GjHlsq 5dHgMbpM550QhTDsvrbYQbpuT8WD2ewydpVaqFJNlaaCUirU6BqGwGZ0cXszXNDpIvV1OCft+1gRd yzkIGSfujyojTXEUUxY1wybieP2DnsJytk16mi/akDgRtliG2WlTWzyQcNnmWdkE1m+dE4SVop4pY xYg/fOUQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98 #2 (Red Hat Linux)) id 1tAoBM-000000033S6-06cq; Tue, 12 Nov 2024 10:31:36 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.98 #2 (Red Hat Linux)) id 1tAnzn-0000000313c-2rd3 for linux-arm-kernel@lists.infradead.org; Tue, 12 Nov 2024 10:19:41 +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 5B44C25E4; Tue, 12 Nov 2024 02:20:08 -0800 (PST) Received: from [10.57.89.175] (unknown [10.57.89.175]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id DA9683F66E; Tue, 12 Nov 2024 02:19:35 -0800 (PST) Message-ID: <5a041e51-a43b-4878-ab68-4757d3141889@arm.com> Date: Tue, 12 Nov 2024 10:19:34 +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> From: Ryan Roberts In-Reply-To: <20241112104544.574dd733@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-20241112_021939_810313_51780396 X-CRM114-Status: GOOD ( 17.52 ) 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 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())? > >> You probably also saw the conversation with Catalin about the cost vs benefit of >> this series. Performance regressions will all need to be considered in the cost >> column, of course. So understanding the root cause and trying to reduce the >> regression as much as possible will increase chances of getting it accepted >> upstream. > > Yes. Now that the biggest number is off the table, I'm going to: > > - look into the dup() slowdown > - verify whether VMA split/merge operations are indeed slower > > Petr T