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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id C2601C35FFA for ; Wed, 19 Mar 2025 10:47:49 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 6129E280002; Wed, 19 Mar 2025 06:47:48 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 5C15B280001; Wed, 19 Mar 2025 06:47:48 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 4661E280002; Wed, 19 Mar 2025 06:47:48 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0013.hostedemail.com [216.40.44.13]) by kanga.kvack.org (Postfix) with ESMTP id 26694280001 for ; Wed, 19 Mar 2025 06:47:48 -0400 (EDT) Received: from smtpin01.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay02.hostedemail.com (Postfix) with ESMTP id 800B1121C60 for ; Wed, 19 Mar 2025 10:47:48 +0000 (UTC) X-FDA: 83237975016.01.EB1339A Received: from mail-wr1-f51.google.com (mail-wr1-f51.google.com [209.85.221.51]) by imf19.hostedemail.com (Postfix) with ESMTP id 905AE1A0004 for ; Wed, 19 Mar 2025 10:47:46 +0000 (UTC) Authentication-Results: imf19.hostedemail.com; dkim=pass header.d=gmail.com header.s=20230601 header.b=Jl6tIc6I; spf=pass (imf19.hostedemail.com: domain of mjguzik@gmail.com designates 209.85.221.51 as permitted sender) smtp.mailfrom=mjguzik@gmail.com; dmarc=pass (policy=none) header.from=gmail.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1742381266; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=W26Wk5z7hiFxOE5qJlj+yFWl9XayBRIq0uAxqiX8N3w=; b=byL/rtN5of2GHB+7q3LeAd4t47ZTPSlfTW/5LnJMIy4LV2dzUjRFOZPap2RHRFnwkTSJia eWB9CmqtUcp7xWBa8ZI9P19k9P0UEDHy7iRJhCoLAPiCjpgjkijPilfGXc/Kb25O1wYJHO adOdurbopqhGeFY4gEPi9Rmjpeq37N0= ARC-Authentication-Results: i=1; imf19.hostedemail.com; dkim=pass header.d=gmail.com header.s=20230601 header.b=Jl6tIc6I; spf=pass (imf19.hostedemail.com: domain of mjguzik@gmail.com designates 209.85.221.51 as permitted sender) smtp.mailfrom=mjguzik@gmail.com; dmarc=pass (policy=none) header.from=gmail.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1742381266; a=rsa-sha256; cv=none; b=GC2vXdzSAppAYiHDng/hXEooILdHDa3TTo9gjT64wNRDW4EcQ5Sxb1jdEGaXM/Yz/K0nfu YtpvjuNfy4vFpifOfrAneiNM/xVkB4ulmuk/EdFKEEWHmjHhhcwiYYaa4Gbm/K6qFkAtyl MdcPWIAc2LYl89diEmTZWo4bSaeMaes= Received: by mail-wr1-f51.google.com with SMTP id ffacd0b85a97d-391342fc1f6so5408892f8f.1 for ; Wed, 19 Mar 2025 03:47:46 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1742381265; x=1742986065; darn=kvack.org; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc:subject:date:message-id:reply-to; bh=W26Wk5z7hiFxOE5qJlj+yFWl9XayBRIq0uAxqiX8N3w=; b=Jl6tIc6IzRQeeUXbuyJmJncqXZht+saSF8bVrFRI+4LgbxzpxnrTfjb8Yx1mtjlbjc EJ1qeL3s5bu/N4tFpCWerQhgEbxJOhcn7OFc4kzTILgNeF4E2Gfj284RN+NEltTK8cmj 16q5qLcl/P9D9vy2mbOE6X1JtUrTPEQ5BWRne5WRksHZ3C3dF2KCbc2rbZWdohD5AFis VH0tEtwoclr96oiBkzRrmw65D/0BBCfQrWX0aKB8ZwvJTt8FfE2wFmsZeK74sL2N6Qt5 Z6SN+0MxKcQ784Kwhivs3C0D3GptFzQ0kKbmexBI2Q/JBNF2GZ35EemazP5h20u98CrH Jfzg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1742381265; x=1742986065; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=W26Wk5z7hiFxOE5qJlj+yFWl9XayBRIq0uAxqiX8N3w=; b=aAet/RXykvXQdjtCH2diP1q/o8O3/iA/qdrvX6/EdiKZGfKKiKRk778W1mekPctcag V6OYh48N8vgN0R7WW68zaPHRl9IgwcR6BPxZeDUSkFugphu3XkD2pcRxH+hw2iLJtYKP eRZ2K0MZV0gmD6jOsigrAzQl9iGNsghViU7QAU/gue7z3mrWLryhMIJvm2/1ra1bQ39c sxtX2WitLkdJc6BOIYNVNIMlWgXPU3XFbANKHE60nQoywZuqkCIhBwA/Xctn9od9IdNl Ur38QK0NatTaIkuK/FVPI8uMIpqiyfp42zhT7b7okht49Qr+4bdBCFfKA338F+Fr/q6q nz9Q== X-Forwarded-Encrypted: i=1; AJvYcCUYPMBCCPEOxHZZ8tvJ7vBw2a2emMjyvrfu0IZYJzhQUz0/LYdkEHhCgjsRkIik5qLYfzwVZ0Or4w==@kvack.org X-Gm-Message-State: AOJu0Yy/XyP05+jg6ANwH4v0+SI6LM/kpQMBbUCqC+8WhVpytGKe6dg0 oLmFgeV5FE2m0AUPL261ZzUnZa1iY/uOa0zNYzCQt2AHlyS8HsC3AUlkKzU9 X-Gm-Gg: ASbGncuz/YENf0ciiBft8vq5cWoDPgMT6B6HImKCOvQAMSX16VvfYHoOCvT/8MH05zt ND+p3qtiyWScwAv61JywEGnInQM5CWYORZPTYEY6I0c5EB0wm5sjhRi3cCo0h9HuCl4DL0gGo2l io3iOczEx51zCDrulPY5tPLt1M2BKu8eDkm+/CR+LGgkt2bJGz/ExQQ9xtpMfWDgk65ztqJIOg8 ZPNNBX0rUpCOiXyrWEw3LKVXhrd6O56tu5YdVwKqKvLJw84u9X1z5fomZNBCR7AJF4t16aN0ChC 7tJgbusX+roL3Bx5xj3JX16lLSr6sQigJLl2qfSjZyIvzPY+5V248ziKYlxnHe3tPRbHHrI= X-Google-Smtp-Source: AGHT+IFeWFBVb117gHRg6qAEPcNELWKw8bczEycMdH3YPjjfnip/JT4VlAY82Ht7iJ8McuMZ7Sag+g== X-Received: by 2002:a05:6000:184d:b0:391:476f:d3b7 with SMTP id ffacd0b85a97d-39973b1d8d3mr1573400f8f.49.1742381264646; Wed, 19 Mar 2025 03:47:44 -0700 (PDT) Received: from f (cst-prg-67-174.cust.vodafone.cz. [46.135.67.174]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-395c8975bdfsm20320478f8f.49.2025.03.19.03.47.40 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 19 Mar 2025 03:47:43 -0700 (PDT) Date: Wed, 19 Mar 2025 11:47:32 +0100 From: Mateusz Guzik To: Greg Thelen Cc: Tejun Heo , Johannes Weiner , Michal =?utf-8?Q?Koutn=C3=BD?= , Andrew Morton , Eric Dumazet , Yosry Ahmed , cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Eric Dumazet Subject: Re: [PATCH] cgroup/rstat: avoid disabling irqs for O(num_cpu) Message-ID: References: <20250319071330.898763-1-gthelen@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20250319071330.898763-1-gthelen@google.com> X-Rspam-User: X-Rspamd-Queue-Id: 905AE1A0004 X-Rspamd-Server: rspam03 X-Stat-Signature: 7puio38anmt3f4g1o14qdh4xft651x8e X-HE-Tag: 1742381266-653519 X-HE-Meta: U2FsdGVkX18+Jr9E2+eb5zx+bnlaCEOAM7aSq/+Gtd6Jhd70QY6tYo7PVEiCLAnGF/5/A0/m+9bSd8O+EKbj4rBJ3a/KizDHVqPenBOwKmCP7zFbleMTVKG/dO3KcSDesZ6Ip5v3R/6T7jarFBXXwRSWuDOJBp6lE85JG9hjw2rclBJtEbc9opceXC28iEHMF+IKAIy9iR3fAANt5bPJeYzLVxKTacvXaiSTPlgPa3OdpYDX3kAobKZvrF6sIJj0a/xeW6Mz4aVg8p/Hx7dEBj4DzSRTmzeZKqC/gk22NkYr4qA/rFUpBzrmj3tUVYC6JV2y+VSlMRrn5S8w/2c7R+k1F+l0CpB+gIg0RTGKu9sKSPVLnAJLesBSmsmUrwtwz23UDMPdg8NKoHIsP1Ahy3fqiJeSJmwWzxm+53TAIOiu8WrPtDOIi6t31hbKtH6xZKkSuyE+FPqaK5p5h5J5iUrGre3a17gAxvoA/M9UHi6RslpzbbIoDT9q2844FpQ1RLSMlq34obFgMuhwE9KI7+jn+A77gOxT+x/LOAS2pQEvJRmnRg1oNRIOX0eCvQ65dZE3yGjuSyF7UCWrTfhjhZvWOh44PuL+IEkzHiS4dKdQvtE+uSZG/pc+DHxQVtC2htr8zrD6QOs6Y7pr9DrX9yJwxRfhqo2D4bD2B0wUk/XEwXzd74a28OGCmcKnXKDZROTeTYakSRZbb/2la1inp0JfeFXjz5/isxobFumZrxlTuAORHvsiJ92tnkwjikHwDSBtHYWZzobDsBErb+H0P3dS0xlG/RvnZUvqck1us1LQPux2Nhslug+CO+z6y47/inZHl0dApZs6LKFfdCYfd/lYI4k1Acnk+T8L7X8imxGkT+ltKtELvd8M19CLBqxJIGxekqNmyivpuN1JiON41npx5gvAu+hpifGzbScOS1p2dfyxcJE4gZOke5GOEofAhqo/viRiz79neP+bT1V HOMzH4Kz 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 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: List-Subscribe: List-Unsubscribe: On Wed, Mar 19, 2025 at 12:13:30AM -0700, Greg Thelen wrote: > From: Eric Dumazet > > cgroup_rstat_flush_locked() grabs the irq safe cgroup_rstat_lock while > iterating all possible cpus. It only drops the lock if there is > scheduler or spin lock contention. If neither, then interrupts can be > disabled for a long time. On large machines this can disable interrupts > for a long enough time to drop network packets. On 400+ CPU machines > I've seen interrupt disabled for over 40 msec. > > Prevent rstat from disabling interrupts while processing all possible > cpus. Instead drop and reacquire cgroup_rstat_lock for each cpu. This > approach was previously discussed in > https://lore.kernel.org/lkml/ZBz%2FV5a7%2F6PZeM7S@slm.duckdns.org/, > though this was in the context of an non-irq rstat spin lock. > > Benchmark this change with: > 1) a single stat_reader process with 400 threads, each reading a test > memcg's memory.stat repeatedly for 10 seconds. > 2) 400 memory hog processes running in the test memcg and repeatedly > charging memory until oom killed. Then they repeat charging and oom > killing. > > v6.14-rc6 with CONFIG_IRQSOFF_TRACER with stat_reader and hogs, finds > interrupts are disabled by rstat for 45341 usec: > # => started at: _raw_spin_lock_irq > # => ended at: cgroup_rstat_flush > # > # > # _------=> CPU# > # / _-----=> irqs-off/BH-disabled > # | / _----=> need-resched > # || / _---=> hardirq/softirq > # ||| / _--=> preempt-depth > # |||| / _-=> migrate-disable > # ||||| / delay > # cmd pid |||||| time | caller > # \ / |||||| \ | / > stat_rea-96532 52d.... 0us*: _raw_spin_lock_irq > stat_rea-96532 52d.... 45342us : cgroup_rstat_flush > stat_rea-96532 52d.... 45342us : tracer_hardirqs_on <-cgroup_rstat_flush > stat_rea-96532 52d.... 45343us : > => memcg1_stat_format > => memory_stat_format > => memory_stat_show > => seq_read_iter > => vfs_read > => ksys_read > => do_syscall_64 > => entry_SYSCALL_64_after_hwframe > > With this patch the CONFIG_IRQSOFF_TRACER doesn't find rstat to be the > longest holder. The longest irqs-off holder has irqs disabled for > 4142 usec, a huge reduction from previous 45341 usec rstat finding. > > Running stat_reader memory.stat reader for 10 seconds: > - without memory hogs: 9.84M accesses => 12.7M accesses > - with memory hogs: 9.46M accesses => 11.1M accesses > The throughput of memory.stat access improves. > > The mode of memory.stat access latency after grouping by of 2 buckets: > - without memory hogs: 64 usec => 16 usec > - with memory hogs: 64 usec => 8 usec > The memory.stat latency improves. > > Signed-off-by: Eric Dumazet > Signed-off-by: Greg Thelen > Tested-by: Greg Thelen > --- > kernel/cgroup/rstat.c | 12 +++++------- > 1 file changed, 5 insertions(+), 7 deletions(-) > > diff --git a/kernel/cgroup/rstat.c b/kernel/cgroup/rstat.c > index aac91466279f..976c24b3671a 100644 > --- a/kernel/cgroup/rstat.c > +++ b/kernel/cgroup/rstat.c > @@ -323,13 +323,11 @@ static void cgroup_rstat_flush_locked(struct cgroup *cgrp) > rcu_read_unlock(); > } > > - /* play nice and yield if necessary */ > - if (need_resched() || spin_needbreak(&cgroup_rstat_lock)) { > - __cgroup_rstat_unlock(cgrp, cpu); > - if (!cond_resched()) > - cpu_relax(); > - __cgroup_rstat_lock(cgrp, cpu); > - } > + /* play nice and avoid disabling interrupts for a long time */ > + __cgroup_rstat_unlock(cgrp, cpu); > + if (!cond_resched()) > + cpu_relax(); > + __cgroup_rstat_lock(cgrp, cpu); > } > } Is not this going a little too far? the lock + irq trip is quite expensive in its own right and now is going to be paid for each cpu, as in the total time spent executing cgroup_rstat_flush_locked is going to go up. Would your problem go away toggling this every -- say -- 8 cpus? Just a suggestion.