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]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 088BFCD4F26 for ; Tue, 12 May 2026 07:49:10 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 6A8416B009B; Tue, 12 May 2026 03:49:09 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 67FEF6B009D; Tue, 12 May 2026 03:49:09 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 5BC536B009E; Tue, 12 May 2026 03:49:09 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0012.hostedemail.com [216.40.44.12]) by kanga.kvack.org (Postfix) with ESMTP id 4B4616B009B for ; Tue, 12 May 2026 03:49:09 -0400 (EDT) Received: from smtpin06.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay05.hostedemail.com (Postfix) with ESMTP id 10BC3403F8 for ; Tue, 12 May 2026 07:49:09 +0000 (UTC) X-FDA: 84757992018.06.AB76D9B Received: from stravinsky.debian.org (stravinsky.debian.org [82.195.75.108]) by imf04.hostedemail.com (Postfix) with ESMTP id 2B3DB40007 for ; Tue, 12 May 2026 07:49:06 +0000 (UTC) Authentication-Results: imf04.hostedemail.com; dkim=pass header.d=debian.org header.s=smtpauto.stravinsky header.b=e76ZAj6c; dmarc=pass (policy=none) header.from=debian.org; spf=pass (imf04.hostedemail.com: domain of leitao@debian.org designates 82.195.75.108 as permitted sender) smtp.mailfrom=leitao@debian.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1778572147; a=rsa-sha256; cv=none; b=lEJ3YQk9/Y9PbV2PBVngkXKde47GEm3ZBl6DU0b/0eQMdMyzSUM63LLIzMlVFUMT9blg2F miUqu0mM4Q9ljwct7o/7jmr6Ag6Sp65Pj/xrlPYX2QFB3oOk3y4avBCZmD39HNx5WXMHif ePWu3qoUtdu5IoNGRRpVE5phKt6WCC8= ARC-Authentication-Results: i=1; imf04.hostedemail.com; dkim=pass header.d=debian.org header.s=smtpauto.stravinsky header.b=e76ZAj6c; dmarc=pass (policy=none) header.from=debian.org; spf=pass (imf04.hostedemail.com: domain of leitao@debian.org designates 82.195.75.108 as permitted sender) smtp.mailfrom=leitao@debian.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1778572147; 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=L9Je9p6iKz0LhJs2B2OBOVnKx7GVs/d3t4vLkYEhSok=; b=V2EaFEiEa4YSuTOhy8c8Soy8kEPm7uG6V5TZoQiE86VqJgND6S3694uGmcTkmoz1URV+Dp rllS48+sFAeWtZQhzLgQheyYIic1voNllPT3C1TpKrjbOcFqXfHRIj1loDosUuUUULlM36 UjWiMqHFQUAz4p4je7LDe4anydvLR2g= DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=debian.org; s=smtpauto.stravinsky; h=X-Debian-User:In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=L9Je9p6iKz0LhJs2B2OBOVnKx7GVs/d3t4vLkYEhSok=; b=e76ZAj6cq9wK8LolMqLtOiipXB N0kHt9swwcOBhSpr0VVJrOWwxxqVm7oztBxdbf5Dyl2AFH547HkdGDAGZCPc3J30LVvCj08AZ7QBs KlqhGZwml1BBrGa/JaEsnm0D0MVsH+wh7W+kiW8E+O1mUQ1W1wwj40xAvCRQJTbQBF3QLKXxrpgym Mj3VB02DVvDanDw11w9pDBKvlqTCdeNlZ6T8KBTyrQST1YypIKh6zJA3g9DKZOsQMEUkSml0D7g/v 0QKsdOFS3rwVMNXRnL3auGlrkBeSRarMwPSAb1CsgHW8eVZ12SYOIpo93dOFdDVrKGbjGuI6sJZ/i S0N3VYIg==; Received: from authenticated user by stravinsky.debian.org with esmtpsa (TLS1.3:ECDHE_X25519__RSA_PSS_RSAE_SHA256__AES_256_GCM:256) (Exim 4.96) (envelope-from ) id 1wMhrD-002E10-01; Tue, 12 May 2026 07:48:47 +0000 Date: Tue, 12 May 2026 00:48:39 -0700 From: Breno Leitao To: Gustavo Luiz Duarte Cc: Joel Fernandes , "Paul E. McKenney" , Frederic Weisbecker , Neeraj Upadhyay , Josh Triplett , Boqun Feng , Uladzislau Rezki , Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , Zqiang , Vlastimil Babka , Harry Yoo , Andrew Morton , Hao Li , Christoph Lameter , David Rientjes , Roman Gushchin , rcu@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH RFC 0/2] rcu: Add debugfs interface for pending callback monitoring Message-ID: References: <20260507-rcu-pending-cbs-stats-v1-0-8f4eb3553bc9@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Debian-User: leitao X-Stat-Signature: az7t4bwmi3ip1wa6fdj13xqh1jxana3t X-Rspam-User: X-Rspamd-Queue-Id: 2B3DB40007 X-Rspamd-Server: rspam07 X-HE-Tag: 1778572146-127521 X-HE-Meta: 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 xrSkRgIi tY2yVJj3dmBvQCADvwK9Sjs9aLpwOtTDgNC+TiduKMUN2oRAo7cJbZBK2DCqVHhHZq0dpCl/5L7QlXEZ7SWQabicKopKP0ZTEkwqkzkVDydnFgie9xRM5ZYhKK/BUcrPDURumPQZyTyiDA8WUBh2FrOYdNA9Dxnijs0xfQaEjSI+q3bu6pBixd6oViHsTHq+gHw8b4K8Fqt3aDfG3kUSeg8agQ2Ev9V1tZNSxPVxaM25++2RI+kN/9dOeRwAtxtA5Qrzt Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, May 11, 2026 at 06:08:53PM +0100, Gustavo Luiz Duarte wrote: > > You actually don't need debugfs for this. You can just use bpftrace and > > instrument trace_rcu_ (with other RCU tracing Kconfig options enabled?). I had > > something like that working sometime ago. > > My initial attempt to do this using tracepoints was probing > trace_rcu_segcb_stats, but this would add significant overhead to > every callback enqueue/dequeue event which is too expensive for a > production environment An additional benefit of this debugfs-based approach is that it eliminates the dependency on bpftrace and custom scripts. While instrumenting tracepoints with bpftrace is certainly feasible for a limited number of servers, deploying it fleet-wide becomes problematic. It requires distributing and maintaining additional binaries on every host, just to collect metrics that a few lines of kernel code can expose more efficiently. So while bpftrace can technically accomplish this, it may not be the most appropriate solution for this particular use case.