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=-2.4 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,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 CB4B9C33CAF for ; Thu, 16 Jan 2020 04:06:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9BF9F20723 for ; Thu, 16 Jan 2020 04:06:01 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=joelfernandes.org header.i=@joelfernandes.org header.b="UWtMAmok" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729850AbgAPEGB (ORCPT ); Wed, 15 Jan 2020 23:06:01 -0500 Received: from mail-pf1-f193.google.com ([209.85.210.193]:41486 "EHLO mail-pf1-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729758AbgAPEGB (ORCPT ); Wed, 15 Jan 2020 23:06:01 -0500 Received: by mail-pf1-f193.google.com with SMTP id w62so9549317pfw.8 for ; Wed, 15 Jan 2020 20:06:00 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=joelfernandes.org; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=R3OaHJ/NoHo97qXRlJsk6XbKoJmXhoMLhGPLnTVZhRI=; b=UWtMAmokJ/P3d7sD2bmYBARu+1sTAP0qHRJ+jyvjczeS0igyZpJ7Pt1ZW27HzvPEtC Qo4e08NcyYbEKQ1o6NW+RInhKWixcbZ0JWw+ToAOCkjpbsioshu+xNiq3jDCiyc0k+0v V68XXLdKiWKW0S+JUsOTO8tFBazj8S9TUPpkA= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=R3OaHJ/NoHo97qXRlJsk6XbKoJmXhoMLhGPLnTVZhRI=; b=Q7731BSkTjNXFNZpdGflI/3t8OUJRyY00AJt1SIdNga33G6W5cJrHuDiVgPUPq4ZJ0 KbVc9sk0mfUTHljNza8I1BePNn9z8Im4RtNKr0qJboZWBBTAOoMIFIXVyJkohwex+a9S CIlO55mvP4tbcMidJ2M0f2Q2Y9xUz4jAMAMvkhxBG2TCwKfn4qnETEHZFpkrMYN9nDdV IlekvblYVygxrq1bTTE48HWAKcMuzoM5kYG0nnprAKyKPGgNdIqE+AoZ980W9awDfiiL Lgx5nKTugg0P99C/VmkdQnh3ant0XD9GLJpnfZbjl95nZKQQJakDuMTyevbjL2cDmyhk 05oA== X-Gm-Message-State: APjAAAVyhRcx+AEyJy5KD8vra7397zjaV0+v02AK9gbxqEcCFOFZb+NN YSEJewzia1RZTLpsTw1VM0MXtg== X-Google-Smtp-Source: APXvYqzbpu+zEroh1lCJNK2RswLPoOkrbl0hdO0L1TFDlTlzeRdWYeqQT/qEldakCQJ9/tQN5n8TmA== X-Received: by 2002:a63:a555:: with SMTP id r21mr36221700pgu.158.1579147560046; Wed, 15 Jan 2020 20:06:00 -0800 (PST) Received: from localhost ([2620:15c:6:12:9c46:e0da:efbf:69cc]) by smtp.gmail.com with ESMTPSA id e15sm785798pja.13.2020.01.15.20.05.59 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 15 Jan 2020 20:05:59 -0800 (PST) Date: Wed, 15 Jan 2020 23:05:58 -0500 From: Joel Fernandes To: "Paul E. McKenney" Cc: linux-kernel@vger.kernel.org, bristot@redhat.com, frextrite@gmail.com, madhuparnabhowmik04@gmail.com, urezki@gmail.com, Davidlohr Bueso , Josh Triplett , Lai Jiangshan , Mathieu Desnoyers , rcu@vger.kernel.org, Steven Rostedt Subject: Re: [PATCH v3 rcu-dev] rcuperf: Measure memory footprint during kfree_rcu() test Message-ID: <20200116040558.GD246464@google.com> References: <20191219211349.235877-1-joel@joelfernandes.org> <20191221000729.GH2889@paulmck-ThinkPad-P72> <20191221033714.GB156579@google.com> <20200106195200.GS13449@paulmck-ThinkPad-P72> <20200115220300.GA94036@google.com> <20200115224251.GK2935@paulmck-ThinkPad-P72> <20200115224542.GB94036@google.com> <20200116000104.GO2935@paulmck-ThinkPad-P72> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200116000104.GO2935@paulmck-ThinkPad-P72> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: rcu-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org On Wed, Jan 15, 2020 at 04:01:04PM -0800, Paul E. McKenney wrote: > On Wed, Jan 15, 2020 at 05:45:42PM -0500, Joel Fernandes wrote: > > On Wed, Jan 15, 2020 at 02:42:51PM -0800, Paul E. McKenney wrote: > > > > [snip] > > > > > > We can certainly refine it further but at this time I am thinking of spending > > > > > > my time reviewing Lai's patches and learning some other RCU things I need to > > > > > > catch up on. If you hate this patch too much, we can also defer this patch > > > > > > review for a bit and I can carry it in my tree for now as it is only a patch > > > > > > to test code. But honestly, in its current form I am sort of happy with it. > > > > > > > > > > OK, I will keep it as is for now and let's look again later on. It is not > > > > > in the bucket for the upcoming merge window in any case, so we do have > > > > > quite a bit of time. > > > > > > > > > > It is not that I hate it, but rather that I want to be able to give > > > > > good answers to questions that might come up. And given that I have > > > > > occasionally given certain people a hard time about their statistics, > > > > > it is only reasonable to expect them to return the favor. I wouldn't > > > > > want you to be caught in the crossfire. ;-) > > > > > > > > Since the weights were concerning, I was thinking of just using a weight of > > > > (1 / N) where N is the number of samples. Essentially taking the average. > > > > That could be simple enough and does not cause your concerns with weight > > > > tuning. I tested it and looks good, I'll post it shortly. > > > > > > YES!!! ;-) > > > > > > Snapshot mem_begin before entering the loop. For the mean value to > > > be solid, you need at least 20-30 samples, which might mean upping the > > > default for kfree_loops. Have an "unsigned long long" to accumulate the > > > sum, which should avoid any possibility of overflow for current systems > > > and for all systems for kfree_loops less than PAGE_SIZE. At which point, > > > forget the "%" stuff and just sum up the si_mem_available() on each pass > > > through the loop. > > > > > > Do the division on exit from the loop, preferably checking for divide > > > by zero. > > > > > > Straightforward, fast, reasonably reliable, and easy to defend. > > > > I mostly did it along these lines. Hopefully the latest posting is reasonable > > enough ;-) I sent it twice because I messed up the authorship (sorry). > > No problem with the authorship-fix resend! > > But let's get this patch consistent with basic statistics! > > You really do need 20-30 samples for an average to mean much. > > Of course, right now you default kfree_loops to 10. You are doing > 8000 kmalloc()/kfree_rcu() loops on each pass. This is large enough > that just dropping the "% 4" should be just fine from the viewpoint of > si_mem_available() overhead. But 8000 allocations and frees should get > done in way less than one second, so kicking the default kfree_loops up > to 30 should be a non-problem. > > Then the patch would be both simpler and statistically valid. > > So could you please stop using me as the middleman in your fight with > the laws of mathematics and get this patch to a defensible state? ;-) The thing is the signal doesn't vary much. I could very well just take one out of the 4 samples and report that. But I still took the average since there are 4 samples. I don't see much point in taking more samples here since I am not concerned that the signal will fluctuate much (and if it really does, then I can easily catch that kind of variation with multiple rcuperf runs). But if you really want though, I can increase the sampling to 20 samples or a number like that and resend it. thanks, - Joel