From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr1-f71.google.com (mail-wr1-f71.google.com [209.85.221.71]) by kanga.kvack.org (Postfix) with ESMTP id BF3B68E0001 for ; Tue, 18 Dec 2018 15:29:36 -0500 (EST) Received: by mail-wr1-f71.google.com with SMTP id l16so5668037wre.6 for ; Tue, 18 Dec 2018 12:29:36 -0800 (PST) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id b125sor2388697wmd.19.2018.12.18.12.29.35 for (Google Transport Security); Tue, 18 Dec 2018 12:29:35 -0800 (PST) MIME-Version: 1.0 References: <20181214171508.7791-1-surenb@google.com> <20181214171508.7791-7-surenb@google.com> <20181217162223.GD2218@hirez.programming.kicks-ass.net> <20181218104622.GB15430@hirez.programming.kicks-ass.net> <20181218173000.GA4733@cmpxchg.org> In-Reply-To: From: Suren Baghdasaryan Date: Tue, 18 Dec 2018 12:29:23 -0800 Message-ID: Subject: Re: [PATCH 6/6] psi: introduce psi monitor Content-Type: text/plain; charset="UTF-8" Sender: owner-linux-mm@kvack.org List-ID: To: Joel Fernandes Cc: Johannes Weiner , Peter Zijlstra , Greg Kroah-Hartman , Tejun Heo , lizefan@huawei.com, axboe@kernel.dk, dennis@kernel.org, Dennis Zhou , Ingo Molnar , Andrew Morton , Jonathan Corbet , cgroups@vger.kernel.org, linux-mm , linux-doc@vger.kernel.org, LKML , kernel-team@android.com On Tue, Dec 18, 2018 at 11:18 AM Joel Fernandes wrote: > > On Tue, Dec 18, 2018 at 9:58 AM 'Suren Baghdasaryan' via kernel-team > wrote: > > > > Current design supports only whole percentages and if userspace needs > > more granularity then it has to use usecs. > > I agree that usecs cover % usecase and "threshold * win / 100" is > > simple enough for userspace to calculate. I'm fine with changing to > > usecs only. > > Suren, please avoid top-posting to LKML. Sorry, did that by accident. > Also I was going to say the same thing, just usecs only is better. Thanks for the input. > thanks, > > - Joel > > On Tue, Dec 18, 2018 at 9:30 AM Johannes Weiner wrote: > > > > > > On Tue, Dec 18, 2018 at 11:46:22AM +0100, Peter Zijlstra wrote: > > > > On Mon, Dec 17, 2018 at 05:21:05PM -0800, Suren Baghdasaryan wrote: > > > > > On Mon, Dec 17, 2018 at 8:22 AM Peter Zijlstra wrote: > > > > > > > > > > How well has this thing been fuzzed? Custom string parser, yay! > > > > > > > > > > Honestly, not much. Normal cases and some obvious corner cases. Will > > > > > check if I can use some fuzzer to get more coverage or will write a > > > > > script. > > > > > I'm not thrilled about writing a custom parser, so if there is a > > > > > better way to handle this please advise. > > > > > > > > The grammar seems fairly simple, something like: > > > > > > > > some-full = "some" | "full" ; > > > > threshold-abs = integer ; > > > > threshold-pct = integer, { "%" } ; > > > > threshold = threshold-abs | threshold-pct ; > > > > window = integer ; > > > > trigger = some-full, space, threshold, space, window ; > > > > > > > > And that could even be expressed as two scanf formats: > > > > > > > > "%4s %u%% %u" , "%4s %u %u" > > > > > > > > which then gets your something like: > > > > > > > > char type[5]; > > > > > > > > if (sscanf(input, "%4s %u%% %u", &type, &pct, &window) == 3) { > > > > // do pct thing > > > > } else if (sscanf(intput, "%4s %u %u", &type, &thres, &window) == 3) { > > > > // do abs thing > > > > } else return -EFAIL; > > > > > > > > if (!strcmp(type, "some")) { > > > > // some > > > > } else if (!strcmp(type, "full")) { > > > > // full > > > > } else return -EFAIL; > > > > > > > > // do more > > > > > > We might want to drop the percentage notation. > > > > > > While it's somewhat convenient, it's also not unreasonable to ask > > > userspace to do a simple "threshold * win / 100" themselves, and it > > > would simplify the interface spec and the parser. > > > > > > Sure, psi outputs percentages, but only for fixed window sizes, so > > > that actually saves us something, whereas this parser here needs to > > > take a fractional anyway. The output is also in decimal notation, > > > which is necessary for granularity. And I really don't think we want > > > to add float parsing on top of this interface spec. > > > > > > So neither the convenience nor the symmetry argument are very > > > compelling IMO. It might be better to just not go there. > > > > -- > > You received this message because you are subscribed to the Google Groups "kernel-team" group. > > To unsubscribe from this group and stop receiving emails from it, send an email to kernel-team+unsubscribe@android.com. > >