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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 23314C07D5A for ; Mon, 27 Nov 2023 10:27:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232924AbjK0K1r (ORCPT ); Mon, 27 Nov 2023 05:27:47 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46912 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232909AbjK0K1o (ORCPT ); Mon, 27 Nov 2023 05:27:44 -0500 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A31C2E1 for ; Mon, 27 Nov 2023 02:27:50 -0800 (PST) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6F719C433C7; Mon, 27 Nov 2023 10:27:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1701080870; bh=mqtFeeqGki//5Nb3R143+AqRimwbXXJttWageC3NiuU=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=OFFL9zxnJAnhIv2QZsihLuUq6mKSrEU3HutEewWqBmC8wj4Ey9kZH08HHHrY0s6OK zJZxiyeDHaSXmt6RujDPBPT7LJnhuRH9OJliQMqLiUJp4RCXcxAYeyVDXQO0JCd49W 1/eL8pYNWxbPBunN/ikK7aPYUr/nI0d2EHTOaXGxw2yoz6PMFwt1FvDvVsUmkD09L5 u2TWtfr0bZ6oFm5a37f1YH5il4ot9Gs6cja1OS1Y66a9X9mqmQfbz9s3dTyGaD1cz1 MOYYUotox20liwe8wOlhOdEtPTGsk7EHvqPuaSiHrypK3q+f/CrUaOAa1Ia9Vk/I6a nuBmvgv0yHIYQ== Date: Mon, 27 Nov 2023 11:27:43 +0100 From: Christian Brauner To: Linus Torvalds Cc: kernel test robot , oe-lkp@lists.linux.dev, lkp@intel.com, linux-kernel@vger.kernel.org, Jann Horn , linux-doc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, intel-gfx@lists.freedesktop.org, linux-fsdevel@vger.kernel.org, gfs2@lists.linux.dev, bpf@vger.kernel.org, ying.huang@intel.com, feng.tang@intel.com, fengwei.yin@intel.com Subject: Re: [linus:master] [file] 0ede61d858: will-it-scale.per_thread_ops -2.9% regression Message-ID: <20231127-kirschen-dissens-b511900fa85a@brauner> References: <202311201406.2022ca3f-oliver.sang@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > So that nobody else would waste any time on this, attached is a new > attempt. This time actually tested *after* the changes. So I've picked up your patch (vfs.misc). It's clever alright so thanks for the comments in there otherwise I would've stared at this for far too long. It's a little unpleasant because of the cast-orama going on before we check the file pointer but I don't see that it's in any way wrong. And given how focussed people are with __fget_* performance I think it might even be the right thing to do. But the cleverness means we have the same logic slightly differently twice. Not too bad ofc but not too nice either especially because that rcu lookup is pretty complicated already. A few days ago I did just write a long explanatory off-list email to someone who had questions about this and who is fairly experienced so we're not making it easy on people. But performance or simplicity; one can't necessarily always have both.