Cover Letter Detail
Show a cover letter.
GET /api/1.2/covers/2235036/?format=api
{ "id": 2235036, "url": "http://patchwork.ozlabs.org/api/1.2/covers/2235036/?format=api", "web_url": "http://patchwork.ozlabs.org/project/linuxppc-dev/cover/20260508131647.43868-1-frederic@kernel.org/", "project": { "id": 2, "url": "http://patchwork.ozlabs.org/api/1.2/projects/2/?format=api", "name": "Linux PPC development", "link_name": "linuxppc-dev", "list_id": "linuxppc-dev.lists.ozlabs.org", "list_email": "linuxppc-dev@lists.ozlabs.org", "web_url": "https://github.com/linuxppc/wiki/wiki", "scm_url": "https://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux.git", "webscm_url": "https://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux.git/", "list_archive_url": "https://lore.kernel.org/linuxppc-dev/", "list_archive_url_format": "https://lore.kernel.org/linuxppc-dev/{}/", "commit_url_format": "https://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux.git/commit/?id={}" }, "msgid": "<20260508131647.43868-1-frederic@kernel.org>", "list_archive_url": "https://lore.kernel.org/linuxppc-dev/20260508131647.43868-1-frederic@kernel.org/", "date": "2026-05-08T13:16:32", "name": "[00/15,v4] tick/sched: Refactor idle cputime accounting", "submitter": { "id": 79411, "url": "http://patchwork.ozlabs.org/api/1.2/people/79411/?format=api", "name": "Frederic Weisbecker", "email": "frederic@kernel.org" }, "mbox": "http://patchwork.ozlabs.org/project/linuxppc-dev/cover/20260508131647.43868-1-frederic@kernel.org/mbox/", "series": [ { "id": 503389, "url": "http://patchwork.ozlabs.org/api/1.2/series/503389/?format=api", "web_url": "http://patchwork.ozlabs.org/project/linuxppc-dev/list/?series=503389", "date": "2026-05-08T13:16:32", "name": "tick/sched: Refactor idle cputime accounting", "version": 4, "mbox": "http://patchwork.ozlabs.org/series/503389/mbox/" } ], "comments": "http://patchwork.ozlabs.org/api/covers/2235036/comments/", "headers": { "Return-Path": "\n <linuxppc-dev+bounces-20610-incoming=patchwork.ozlabs.org@lists.ozlabs.org>", "X-Original-To": [ "incoming@patchwork.ozlabs.org", "linuxppc-dev@lists.ozlabs.org" ], "Delivered-To": "patchwork-incoming@legolas.ozlabs.org", "Authentication-Results": [ "legolas.ozlabs.org;\n\tdkim=fail reason=\"signature verification failed\" (2048-bit key;\n unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256\n header.s=k20201202 header.b=MGP5FK9r;\n\tdkim-atps=neutral", "legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=lists.ozlabs.org\n (client-ip=112.213.38.117; helo=lists.ozlabs.org;\n envelope-from=linuxppc-dev+bounces-20610-incoming=patchwork.ozlabs.org@lists.ozlabs.org;\n receiver=patchwork.ozlabs.org)", "lists.ozlabs.org;\n arc=none smtp.remote-ip=172.234.252.31", "lists.ozlabs.org;\n dmarc=pass (p=quarantine dis=none) header.from=kernel.org", "lists.ozlabs.org;\n\tdkim=pass (2048-bit key;\n unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256\n header.s=k20201202 header.b=MGP5FK9r;\n\tdkim-atps=neutral", "lists.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=kernel.org\n (client-ip=172.234.252.31; helo=sea.source.kernel.org;\n envelope-from=frederic@kernel.org; receiver=lists.ozlabs.org)" ], "Received": [ "from lists.ozlabs.org (lists.ozlabs.org [112.213.38.117])\n\t(using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits)\n\t key-exchange x25519 server-signature ECDSA (secp384r1 raw public key)\n server-digest SHA384)\n\t(No client certificate requested)\n\tby legolas.ozlabs.org (Postfix) with ESMTPS id 4gBqR01y3Xz1yJq\n\tfor <incoming@patchwork.ozlabs.org>; Fri, 08 May 2026 23:17:15 +1000 (AEST)", "from boromir.ozlabs.org (localhost [127.0.0.1])\n\tby lists.ozlabs.org (Postfix) with ESMTP id 4gBqQy2FYCz2xfR;\n\tFri, 08 May 2026 23:17:14 +1000 (AEST)", "from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31])\n\t(using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits)\n\t key-exchange x25519 server-signature RSA-PSS (2048 bits) server-digest\n SHA256)\n\t(No client certificate requested)\n\tby lists.ozlabs.org (Postfix) with ESMTPS id 4gBqQs1gygz2xQC\n\tfor <linuxppc-dev@lists.ozlabs.org>; Fri, 08 May 2026 23:17:09 +1000 (AEST)", "from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58])\n\tby sea.source.kernel.org (Postfix) with ESMTP id DBA24437E8;\n\tFri, 8 May 2026 13:17:06 +0000 (UTC)", "by smtp.kernel.org (Postfix) with ESMTPSA id CB1B3C2BCB0;\n\tFri, 8 May 2026 13:16:58 +0000 (UTC)" ], "ARC-Seal": "i=1; a=rsa-sha256; d=lists.ozlabs.org; s=201707; t=1778246234;\n\tcv=none;\n b=dKuD0bz89ZCIB+EVYCwRfCG8ITH+1A+J8ZvdkAtrUwaPH/o6CjfN73cUyKLHIV7yj7II20ph2lvULeEscz7hQXg/ms7G15CfUoCA2IFL/4zQU34kqRDKiLrlwAszDZyC2Sd6zXQE4BwpC082p2ZLyqa/VDpKI5HESlfzWJi24RHQkMip/fIZlJmPsBREiE60iTEJhrj2xElWjXnqgobdwN0U7iQ1o82xOdAcsBOKIpThzThTK58JcrVqfHbgzYB2m6UWNNAHU2uu2Cctj4XFrf7UyZZdS66Hd5r9CS5AFCV24kowAJm656fxmuc/wE448X6IVh0FSA+TPsOxpHKNlQ==", "ARC-Message-Signature": "i=1; a=rsa-sha256; d=lists.ozlabs.org; s=201707;\n\tt=1778246234; c=relaxed/relaxed;\n\tbh=KSR3buBUoGn7h6QUFUsLNU/EqeWQM09a7paH2USs2Dg=;\n\th=From:To:Cc:Subject:Date:Message-ID:MIME-Version;\n b=FfLLVWFKt9xleLo0U1WKHFmVBkStTYXh+5kpsY/8+aBz0B2Wpo7VFciTMJLKuW5UA4KzjRId32cZ8YUTQtGXwopND0Iplgm5Ov45RAdRmmksBz9hJKYWIwPwQMdW6j3r9KIC5UUm7q2X8q+hukVpTDZ0Y8Gk1FZLYSeSXHf2PTLtw1++nhjDkxp/blIRxUUUOH9bbuZBiCmA48F5/yMW7O/wTsCN0TeiC6/FMPZMBjxWrWUkOzQax9+xmRYPBw0zTnqokCcyQ0enM3juoc0Bh9qZCoksw9on+XUdGLTjcOni31u+CrOAkJ1EfRP2l4bazsiFAvhyPYowMCMQ9aUmSQ==", "ARC-Authentication-Results": "i=1; lists.ozlabs.org;\n dmarc=pass (p=quarantine dis=none) header.from=kernel.org;\n dkim=pass (2048-bit key;\n unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256\n header.s=k20201202 header.b=MGP5FK9r; dkim-atps=neutral;\n spf=pass (client-ip=172.234.252.31; helo=sea.source.kernel.org;\n envelope-from=frederic@kernel.org;\n receiver=lists.ozlabs.org) smtp.mailfrom=kernel.org", "DKIM-Signature": "v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org;\n\ts=k20201202; t=1778246226;\n\tbh=Vta7hllmwFIumsR7obeWKsvWVRLZq990abYtI1WVcNk=;\n\th=From:To:Cc:Subject:Date:From;\n\tb=MGP5FK9r9QEOy860Im4ejrteL4FwEhVVu14vipu9Z+cC0I316uNQwgOy0hPfLaVhY\n\t zQhpMRfoyyqaX7J92xkQ+LLBJPltZMpkOyxK8CW1LDab4vsyBS15jl9dAajLFcYQ+d\n\t kK5YF3Hom2fADVLNDaSgsqvXA0DaQeukbeZ8GVvmIZvU7rBkXPEHxGdUBBENsvirza\n\t ARd5MU8U0tleul+fXPjitjj+XOBfZwXLfuLAE6K8/NWnjBl5m1NH7Ymk0sokSPUqTJ\n\t I2DswfY8YWOGs4TB0lt1eaRgSZBvqBl+VOwwXu2m22zdvgatVVuQ0wwR7N55pFdd2N\n\t d+E2RmzRgmsqQ==", "From": "Frederic Weisbecker <frederic@kernel.org>", "To": "LKML <linux-kernel@vger.kernel.org>", "Cc": "Frederic Weisbecker <frederic@kernel.org>,\n\tMadhavan Srinivasan <maddy@linux.ibm.com>,\n\tPeter Zijlstra <peterz@infradead.org>,\n\tJan Kiszka <jan.kiszka@siemens.com>,\n\tDietmar Eggemann <dietmar.eggemann@arm.com>,\n\tShrikanth Hegde <sshegde@linux.ibm.com>,\n\tNicholas Piggin <npiggin@gmail.com>,\n\tAlexander Gordeev <agordeev@linux.ibm.com>,\n\tBen Segall <bsegall@google.com>,\n\tThomas Gleixner <tglx@linutronix.de>,\n\tVasily Gorbik <gor@linux.ibm.com>,\n\t\"Rafael J. Wysocki\" <rafael@kernel.org>, linux-pm@vger.kernel.org,\n\tSashiko@lists.ozlabs.org, Ingo Molnar <mingo@kernel.org>,\n\tMichael Ellerman <mpe@ellerman.id.au>,\n\tBoqun Feng <boqun.feng@gmail.com>,\n\tValentin Schneider <vschneid@redhat.com>,\n\tlinuxppc-dev@lists.ozlabs.org, Sven Schnelle <svens@linux.ibm.com>,\n\tIngo Molnar <mingo@redhat.com>,\n\tVincent Guittot <vincent.guittot@linaro.org>,\n\tChristian Borntraeger <borntraeger@linux.ibm.com>,\n\tMel Gorman <mgorman@suse.de>, Steven Rostedt <rostedt@goodmis.org>,\n\tJoel Fernandes <joelagnelf@nvidia.com>,\n\t\"Paul E . McKenney\" <paulmck@kernel.org>,\n\tNeeraj Upadhyay <neeraj.upadhyay@kernel.org>,\n\tAnna-Maria Behnsen <anna-maria@linutronix.de>,\n\t\"Christophe Leroy (CS GROUP)\" <chleroy@kernel.org>,\n\tJuri Lelli <juri.lelli@redhat.com>,\n\tUladzislau Rezki <urezki@gmail.com>,\n\tViresh Kumar <viresh.kumar@linaro.org>,\n\tKieran Bingham <kbingham@kernel.org>,\n\tXin Zhao <jackzxcui1989@163.com>, linux-s390@vger.kernel.org,\n\tHeiko Carstens <hca@linux.ibm.com>", "Subject": "[PATCH 00/15 v4] tick/sched: Refactor idle cputime accounting", "Date": "Fri, 8 May 2026 15:16:32 +0200", "Message-ID": "<20260508131647.43868-1-frederic@kernel.org>", "X-Mailer": "git-send-email 2.53.0", "X-Mailing-List": "linuxppc-dev@lists.ozlabs.org", "List-Id": "<linuxppc-dev.lists.ozlabs.org>", "List-Help": "<mailto:linuxppc-dev+help@lists.ozlabs.org>", "List-Owner": "<mailto:linuxppc-dev+owner@lists.ozlabs.org>", "List-Post": "<mailto:linuxppc-dev@lists.ozlabs.org>", "List-Archive": "<https://lore.kernel.org/linuxppc-dev/>,\n <https://lists.ozlabs.org/pipermail/linuxppc-dev/>", "List-Subscribe": "<mailto:linuxppc-dev+subscribe@lists.ozlabs.org>,\n <mailto:linuxppc-dev+subscribe-digest@lists.ozlabs.org>,\n <mailto:linuxppc-dev+subscribe-nomail@lists.ozlabs.org>", "List-Unsubscribe": "<mailto:linuxppc-dev+unsubscribe@lists.ozlabs.org>", "Precedence": "list", "MIME-Version": "1.0", "Content-Transfer-Encoding": "8bit", "X-Spam-Status": "No, score=-0.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED,\n\tDKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,SPF_HELO_NONE,SPF_PASS\n\tautolearn=disabled version=4.0.1 OzLabs 8", "X-Spam-Checker-Version": "SpamAssassin 4.0.1 (2024-03-25) on lists.ozlabs.org" }, "content": "Hi,\n\nAfter the issue reported here:\n\n https://lore.kernel.org/all/20251210083135.3993562-1-jackzxcui1989@163.com/\n\nIt occurs that the idle cputime accounting is a big mess that\naccumulates within two concurrent statistics, each having their own\nshortcomings:\n\n* The accounting for online CPUs which is based on the delta between\n tick_nohz_start_idle() and tick_nohz_stop_idle().\n\n Pros:\n - Works when the tick is off\n\n - Has nsecs granularity\n\n Cons:\n - Account idle steal time but doesn't substract it from idle\n cputime.\n\n - Assumes CONFIG_IRQ_TIME_ACCOUNTING by not accounting IRQs but\n the IRQ time is simply ignored when\n CONFIG_IRQ_TIME_ACCOUNTING=n\n\n - The windows between 1) idle task scheduling and the first call\n to tick_nohz_start_idle() and 2) idle task between the last\n tick_nohz_stop_idle() and the rest of the idle time are\n blindspots wrt. cputime accounting (though mostly insignificant\n amount)\n\n - Relies on private fields outside of kernel stats, with specific\n accessors.\n\n* The accounting for offline CPUs which is based on ticks and the\n jiffies delta during which the tick was stopped.\n\n Pros:\n - Handles steal time correctly\n\n - Handle CONFIG_IRQ_TIME_ACCOUNTING=y and\n CONFIG_IRQ_TIME_ACCOUNTING=n correctly.\n\n - Handles the whole idle task\n\n - Accounts directly to kernel stats, without midlayer accumulator.\n\n Cons:\n - Doesn't elapse when the tick is off, which doesn't make it\n suitable for online CPUs.\n\n - Has TICK_NSEC granularity (jiffies)\n\n - Needs to track the dyntick-idle ticks that were accounted and\n substract them from the total jiffies time spent while the tick\n was stopped. This is an ugly workaround.\n\nHaving two different accounting for a single context is not the only\nproblem: since those accountings are of different natures, it is\npossible to observe the global idle time going backward after a CPU goes\noffline, as reported by Xin Zhao.\n\nClean up the situation with introducing a hybrid approach that stays\ncoherent, fixes the backward jumps and works for both online and offline\nCPUs:\n\n* Tick based or native vtime accounting operate before the tick is\n stopped and resumes once the tick is restarted.\n\n* When the idle loop starts, switch to dynticks-idle accounting as is\n done currently, except that the statistics accumulate directly to the\n relevant kernel stat fields.\n\n* Private dyntick cputime accounting fields are removed.\n\n* Works on both online and offline case.\n\n* Move most of the relevant code to the common sched/cputime subsystem\n\n* Handle CONFIG_IRQ_TIME_ACCOUNTING=n correctly such that the\n dynticks-idle accounting still elapses while on IRQs.\n\n* Correctly substract idle steal cputime from idle time\n\nChanges since v3 (among which a lot of relevant reviews from Sashiko):\n\n- Add new tags\n\n- Rebase on latest -rc1\n\n- Add \"tick/sched: Fix TOCTOU in nohz idle time fetch\" (Sashiko)\n\n- Fix buggy state refetch in kcpustat_cpu_fetch_vtime() (Sashiko)\n\n- Fix build issue on powerpc (Christophe Leroy)\n\n- Fix s390 lost steal time occuring on idle IRQs (call vtime_flush() on\n vtime_account_hardirq() and vtime_account_softirq()) (Sashiko)\n\n- Fix build issue on s390\n\n- Fix uninitialized idle_sleeptime_seq (Sashiko)\n\n- Fix irqtime being disabled or enabled in the middle of an idle IRQ\n (Sashiko)\n \n- Fix tick restart and then restop in the same idle loop (Sashiko)\n\n- Fix \"sched/cputime: Handle idle irqtime gracefully\" changelog (Sashiko)\n\n- Fix idle steal time substracted from the wrong index between idle and\n iowait kcpustat. (Sashiko)\n\ngit://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks.git\n\ttimers/core-v4\n\nHEAD: e64ba052ce04e363ff76d3cb8bedc5f812188acb\nThanks,\n\tFrederic\n---\n\nFrederic Weisbecker (15):\n tick/sched: Fix TOCTOU in nohz idle time fetch\n sched/idle: Handle offlining first in idle loop\n sched/cputime: Remove superfluous and error prone kcpustat_field() parameter\n sched/cputime: Correctly support generic vtime idle time\n powerpc/time: Prepare to stop elapsing in dynticks-idle\n s390/time: Prepare to stop elapsing in dynticks-idle\n tick/sched: Unify idle cputime accounting\n tick/sched: Remove nohz disabled special case in cputime fetch\n tick/sched: Move dyntick-idle cputime accounting to cputime code\n tick/sched: Remove unused fields\n tick/sched: Account tickless idle cputime only when tick is stopped\n tick/sched: Consolidate idle time fetching APIs\n sched/cputime: Provide get_cpu_[idle|iowait]_time_us() off-case\n sched/cputime: Handle idle irqtime gracefully\n sched/cputime: Handle dyntick-idle steal time correctly\n\n arch/powerpc/kernel/time.c | 41 +++++\n arch/s390/include/asm/idle.h | 2 +\n arch/s390/kernel/idle.c | 5 +-\n arch/s390/kernel/vtime.c | 75 ++++++++-\n drivers/cpufreq/cpufreq.c | 29 +---\n drivers/cpufreq/cpufreq_governor.c | 6 +-\n drivers/macintosh/rack-meter.c | 2 +-\n fs/proc/stat.c | 40 +----\n fs/proc/uptime.c | 8 +-\n include/linux/kernel_stat.h | 76 +++++++--\n include/linux/tick.h | 4 -\n include/linux/vtime.h | 22 ++-\n kernel/rcu/tree.c | 9 +-\n kernel/rcu/tree_stall.h | 7 +-\n kernel/sched/core.c | 6 +-\n kernel/sched/cputime.c | 308 +++++++++++++++++++++++++++++++------\n kernel/sched/idle.c | 13 +-\n kernel/time/tick-sched.c | 212 ++++++-------------------\n kernel/time/tick-sched.h | 12 --\n kernel/time/timer_list.c | 6 +-\n scripts/gdb/linux/timerlist.py | 4 -\n 21 files changed, 529 insertions(+), 358 deletions(-)" }