From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wr1-f41.google.com (mail-wr1-f41.google.com [209.85.221.41]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8F6001FDE14 for ; Fri, 5 Sep 2025 08:53:21 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.221.41 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1757062403; cv=none; b=EHekIdOWxXVFhwzu5CwxXt4CDZqKkr+6XDKQJJ49GswMpyIPn9fbG+f1i0izzQ0SmxR8dl6nlwEEuOxd1Z6KoxxXvDC63umqJSdjqI3dn7jjJ0Muqs/fkhFubyY+b6pAViME327Ybrpt/npkaMRtgVlYqyJUf6pOXflE8dhgz2g= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1757062403; c=relaxed/simple; bh=PetPyduZIpB/oPcqQW6IpqKbYzqz/tqiYuaPOWMx4vM=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version:Content-Type; b=jwl69ENghl9IrGT3NLb5Ag0NhwPIa21IEPtjjTQWVH06JzpSASRk/ufKaJ6LLD5yBR5pX5jpIlpt7eOhsY3tEvABKy9yyWKO82TasKLdMZhKRozAXZ0B+gvpPT4fY1GmRd9+MZ3KL2KROCl8BV/cqHHWq8E7XzY0L+CM12ZXWig= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=suse.com; spf=pass smtp.mailfrom=suse.com; dkim=pass (2048-bit key) header.d=suse.com header.i=@suse.com header.b=axQEgHSr; arc=none smtp.client-ip=209.85.221.41 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=suse.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=suse.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=suse.com header.i=@suse.com header.b="axQEgHSr" Received: by mail-wr1-f41.google.com with SMTP id ffacd0b85a97d-3c68ac7e18aso1252976f8f.2 for ; Fri, 05 Sep 2025 01:53:21 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=google; t=1757062400; x=1757667200; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:from:to:cc:subject:date:message-id:reply-to; bh=/NgQ8QPnuRQit7aGJLu142RMrYg/y2W1c0W+2cPMojw=; b=axQEgHSr24ZBiwhpTR7ma8FFwvZxBgfFClVXgXwGORXews9Kdy4cQPvYMjdyeApy5A kjgUAa5WIS4svLsLLLLOsgcWsiMUlYlh7QgDAjrObpH3R5pHfb2w0JQ1QoAdzBlWLO6e K5Ug6FZFJMt4JfNzFcYPmcQccU/4S3Az3IelTm7ra9rbK4nRiUBQhkeiAvjC/4EBLCe+ Rt1xNuTOH4zZwhMnTow7xSHchCv5z/gwZeONQ6sSJZzI5MpvpuB/gzczVEv3OFcCdtuY yM361br6/Msz1Sc6Y2y40gek93nWL8pvxom/UsW+W+6hgXmT+M6GW/Q6vKsXvgU5DqXy J/dQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1757062400; x=1757667200; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=/NgQ8QPnuRQit7aGJLu142RMrYg/y2W1c0W+2cPMojw=; b=MLFUd9Weh4kEfg+fvRQAUWa3bYt2/On4MfIltNFN0oDNkSWRPI3FlCUw9mgRk2tEV9 QJo4kBokb4uEi2vIuz2HEBXeFUJB0iLEMIigJ+M950shjFxBkrSFlXZOAa//uBuSia3s bruEDMSkE6xW3N9Lu21ER3Yr4YR9+CXFBedem61fXS7+rPww2zEM4AN0eDWWdhnjzPZn NKi9ziaJDX9Z07yaJvSr4OfriRtectxlLfIB8mDx04pZD8hvIKiuWzZC7RL2UJplYSN7 vOpufASI5hEVC9da5gxTJwVhyRBZr3EzXy2xZQhtzVpZhPJJ4YhECkljxoMw7s7RC2ek BQFQ== X-Forwarded-Encrypted: i=1; AJvYcCVDnAOJNl8rdR/0McPblJuFpphA67BwfIWSq81ceH0enbM0vSlJJIeRuwq1zuiN56J7Yro=@vger.kernel.org X-Gm-Message-State: AOJu0YxgIViCXwRg9L7R44lCPOVbEUKIEKCa1IxOVufqZU0uQhNopCLA OMx0OoYU53U6cwe7VOtH45ofqShuioKmrYIrIt4hr9KdHkcsTjhoMxbsmapfM1qLd8E= X-Gm-Gg: ASbGncsQ8G482Gzl0WjN8JnwcIa03M2e1dGi2M1Mrq3HtXpJ6Ym3Yo7l2wGYoeU7jRK YHhPp2PqyA0yFBZtuC+h4WlpMSUHv4ba9xmhdMtkLoKJeaJdlj8WNvmFhxt2oABV2TKPReOJlYw jL0TSnBppsq/fTJmwSrbxZNiJsM18rK7aRfL9nbRWFchbzkpY580wN606bWl77PGcryVjAmMfjQ 1wzAuE4OOj2gICPLb7J7RLgqjKdfGcqn9ea5aq8hWmAVqyQLDx5edMw6LpcM0DrHMen3yJ8w0rX MNxRO5s5v+rZz8T8Ab9fdlgps7WNkSGv9jDoLjIN5Q1a2yoeNIcHro2H+108GZBQYZwH4xQA9zj vTXnhqKgvT6cTsEIeHv/tRUue6Ytljn64sUTTr9/SuWQLGvDNYCxVNANTbQ== X-Google-Smtp-Source: AGHT+IHQl9jksdiN442oocqmuwM+Cn7y2/9wJITXpvg1zDy2P0is4gUPdRpKYpRdOz1I/pmegtbqGQ== X-Received: by 2002:a05:6000:4022:b0:3d8:1f1b:9c9f with SMTP id ffacd0b85a97d-3d81f1b9fcemr12241560f8f.55.1757062399707; Fri, 05 Sep 2025 01:53:19 -0700 (PDT) Received: from localhost.localdomain ([2a00:6d43:105:c401:e307:1a37:2e76:ce91]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3d729a96912sm18487293f8f.8.2025.09.05.01.53.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 05 Sep 2025 01:53:19 -0700 (PDT) From: Marco Crivellari To: linux-kernel@vger.kernel.org, bpf@vger.kernel.org Cc: Tejun Heo , Lai Jiangshan , Frederic Weisbecker , Sebastian Andrzej Siewior , Marco Crivellari , Michal Hocko , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko Subject: [PATCH 0/3] bpf: replace wq users and add WQ_PERCPU to alloc_workqueue() users Date: Fri, 5 Sep 2025 10:53:06 +0200 Message-ID: <20250905085309.94596-1-marco.crivellari@suse.com> X-Mailer: git-send-email 2.51.0 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Hi! Below is a summary of a discussion about the Workqueue API and cpu isolation considerations. Details and more information are available here: "workqueue: Always use wq_select_unbound_cpu() for WORK_CPU_UNBOUND." https://lore.kernel.org/all/20250221112003.1dSuoGyc@linutronix.de/ === Current situation: problems === Let's consider a nohz_full system with isolated CPUs: wq_unbound_cpumask is set to the housekeeping CPUs, for !WQ_UNBOUND the local CPU is selected. This leads to different scenarios if a work item is scheduled on an isolated CPU where "delay" value is 0 or greater then 0: schedule_delayed_work(, 0); This will be handled by __queue_work() that will queue the work item on the current local (isolated) CPU, while: schedule_delayed_work(, 1); Will move the timer on an housekeeping CPU, and schedule the work there. Currently if a user enqueue a work item using schedule_delayed_work() the used wq is "system_wq" (per-cpu wq) while queue_delayed_work() use WORK_CPU_UNBOUND (used when a cpu is not specified). The same applies to schedule_work() that is using system_wq and queue_work(), that makes use again of WORK_CPU_UNBOUND. This lack of consistentcy cannot be addressed without refactoring the API. === Plan and future plans === This patchset is the first stone on a refactoring needed in order to address the points aforementioned; it will have a positive impact also on the cpu isolation, in the long term, moving away percpu workqueue in favor to an unbound model. These are the main steps: 1) API refactoring (that this patch is introducing) - Make more clear and uniform the system wq names, both per-cpu and unbound. This to avoid any possible confusion on what should be used. - Introduction of WQ_PERCPU: this flag is the complement of WQ_UNBOUND, introduced in this patchset and used on all the callers that are not currently using WQ_UNBOUND. WQ_UNBOUND will be removed in a future release cycle. Most users don't need to be per-cpu, because they don't have locality requirements, because of that, a next future step will be make "unbound" the default behavior. 2) Check who really needs to be per-cpu - Remove the WQ_PERCPU flag when is not strictly required. 3) Add a new API (prefer local cpu) - There are users that don't require a local execution, like mentioned above; despite that, local execution yeld to performance gain. This new API will prefer the local execution, without requiring it. === Introduced Changes by this series === 1) [P 1-2] Replace use of system_wq and system_unbound_wq system_wq is a per-CPU workqueue, but his name is not clear. system_unbound_wq is to be used when locality is not required. Because of that, system_wq has been renamed in system_percpu_wq, and system_unbound_wq has been renamed in system_dfl_wq. 2) [P 3] add WQ_PERCPU to remaining alloc_workqueue() users Every alloc_workqueue() caller should use one among WQ_PERCPU or WQ_UNBOUND. This is actually enforced warning if both or none of them are present at the same time. WQ_UNBOUND will be removed in a next release cycle. === For Maintainers === There are prerequisites for this series, already merged in the master branch. The commits are: 128ea9f6ccfb6960293ae4212f4f97165e42222d ("workqueue: Add system_percpu_wq and system_dfl_wq") 930c2ea566aff59e962c50b2421d5fcc3b98b8be ("workqueue: Add new WQ_PERCPU flag") Thanks! Marco Crivellari (3): bpf: replace use of system_wq with system_percpu_wq bpf: replace use of system_unbound_wq with system_dfl_wq bpf: WQ_PERCPU added to alloc_workqueue users kernel/bpf/cgroup.c | 5 +++-- kernel/bpf/cpumap.c | 2 +- kernel/bpf/helpers.c | 4 ++-- kernel/bpf/memalloc.c | 2 +- kernel/bpf/syscall.c | 2 +- 5 files changed, 8 insertions(+), 7 deletions(-) -- 2.51.0