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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 E7A63C433E0 for ; Fri, 29 May 2020 05:33:35 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 924852074B for ; Fri, 29 May 2020 05:33:35 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 924852074B Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linutronix.de Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id E361B8001A; Fri, 29 May 2020 01:33:34 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id DE70C80010; Fri, 29 May 2020 01:33:34 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id CFC468001A; Fri, 29 May 2020 01:33:34 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0095.hostedemail.com [216.40.44.95]) by kanga.kvack.org (Postfix) with ESMTP id B85CD80010 for ; Fri, 29 May 2020 01:33:34 -0400 (EDT) Received: from smtpin01.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id 7304A180AD81D for ; Fri, 29 May 2020 05:33:34 +0000 (UTC) X-FDA: 76868639148.01.shake12_3c3764f10f35d Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin01.hostedemail.com (Postfix) with ESMTP id 560B91800E8C3 for ; Fri, 29 May 2020 05:33:34 +0000 (UTC) X-HE-Tag: shake12_3c3764f10f35d X-Filterd-Recvd-Size: 4826 Received: from Galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) by imf48.hostedemail.com (Postfix) with ESMTP for ; Fri, 29 May 2020 05:33:33 +0000 (UTC) Received: from p5de0bf0b.dip0.t-ipconnect.de ([93.224.191.11] helo=nanos.tec.linutronix.de) by Galois.linutronix.de with esmtpsa (TLS1.2:DHE_RSA_AES_256_CBC_SHA256:256) (Exim 4.80) (envelope-from ) id 1jeXcw-0004zn-0U; Fri, 29 May 2020 07:32:18 +0200 Received: by nanos.tec.linutronix.de (Postfix, from userid 1000) id 2A083100C2D; Fri, 29 May 2020 07:32:17 +0200 (CEST) From: Thomas Gleixner To: Axel Rasmussen , Andrew Morton , David Rientjes , Davidlohr Bueso , Ingo Molnar , Ingo Molnar , Jerome Glisse , Laurent Dufour , "Liam R . Howlett" , Matthew Wilcox , Michel Lespinasse , Peter Zijlstra , Vlastimil Babka , Will Deacon Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, AKASHI Takahiro , Aleksa Sarai , Alexander Potapenko , Alexey Dobriyan , Al Viro , Andrei Vagin , Ard Biesheuvel , Brendan Higgins , chenqiwu , Christian Brauner , Christian Kellner , Corentin Labbe , Daniel Jordan , Dan Williams , David Gow , "David S. Miller" , "Dmitry V. Levin" , "Eric W. Biederman" , Eugene Syromiatnikov , Jamie Liu , Jason Gunthorpe , John Garry , John Hubbard , Jonathan Adams , Junaid Shahid , Kees Cook , "Kirill A. Shutemov" , Konstantin Khlebnikov , Krzysztof Kozlowski , Mark Rutland , Masahiro Yamada , Masami Hiramatsu , Mathieu Desnoyers , Michal Hocko , Mikhail Zaslonko , Petr Mladek , Ralph Campbell , Randy Dunlap , Roman Gushchin , Shakeel Butt , Steven Rostedt , Tal Gilboa , Uwe =?utf-8?Q?Kleine-K=C3=B6nig?= , Vincenzo Frascino , Yang Shi , Yu Zhao , Axel Rasmussen Subject: Re: [PATCH v2 0/7] Add histogram measuring mmap_lock contention latency In-Reply-To: <20200528235238.74233-1-axelrasmussen@google.com> References: <20200528235238.74233-1-axelrasmussen@google.com> Date: Fri, 29 May 2020 07:32:17 +0200 Message-ID: <87wo4vmhlq.fsf@nanos.tec.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 X-Rspamd-Queue-Id: 560B91800E8C3 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam03 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Axel, Axel Rasmussen writes: > The overall goal of this patchset is to add a latency histogram which measures > `mmap_lock` acquisition time. This is useful to measure the impact of ongoing > work like maple trees and range locks (https://lwn.net/Articles/787629/), and > it is also useful to debug userspace processes which experience long waits due > to lock contention. > > This patchset is built upon walken@google.com's new `mmap_lock` API > (https://lkml.org/lkml/2020/4/21/1307). In its current form, it should apply > cleanly to a 5.7-rc7 tree to which Michel's patchset has already been applied. > > To summarize the changes being made at a high level: > > - Add a histogram library: a `struct histogram` is effectively an array of > thresholds (i.e., buckets), and an array of per-cpu `u64` counts of the > number of samples in each bucket. this is maybe a redundant question as I did not follow the V1 submission. Why do we need yet another histogram mechanism for instrumentation purposes? ftrace has histogram support already. Why can't this be reused? Thanks, tglx