From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2D8FE35963; Thu, 17 Jul 2025 16:04:01 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1752768241; cv=none; b=neSb9vWmOEaQwHilHnOKng9OjBzOdEPDxFpnYPfV+uQBBB6cLznVrTnluiqGIDue7nNp8m9sv/yIAXVnR5qRRNmRMjd4KsyCclcF1U5bCR0MnGHZQ7iQVKbAKZxXdd9+RlxF3witGfZDqeNaT4kIqlRDBgrWd1wgxtvz7ipgbzU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1752768241; c=relaxed/simple; bh=Ql40KFJ+kQuxrg56fLq03oBwJa9AGIhjbEY6BnbzsmM=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=KJXPxDhDqjLP9w4HKw60TQkS1cG40UmeDTxTl4jnTaw0HJipUjHB5EKez2qsTOzwTQX5l1x9NOfPGJMTnPQioDrJW2mZmgubpVZTSnkkqGkeHP5Y2KRZF18U6SNMPNVNIc9RdHg7kpbHpksmact7ERt14erGK801owWHbHcOmCU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=nq6hYFFp; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="nq6hYFFp" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 01E3BC4CEE3; Thu, 17 Jul 2025 16:04:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1752768241; bh=Ql40KFJ+kQuxrg56fLq03oBwJa9AGIhjbEY6BnbzsmM=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=nq6hYFFpb9OoQom7Cb+ncofeV9J9HsZCbcL0aFBxDsahigGVsxH8XsUpt4OpVTwfb zj8hS/YHHyIDccK8EdRzJd6kWgnw+HzrGv2t+s+dViKj2snN2XIZHBcYOSneZMvYPB kfOm17WiNFFlnDIG4kzFY52IdESZX2dF76eGx/Ot20eSlBPM4qM+QHmkfRdu4jWmLZ Do6hEbET0QkQWElbK8RPiNX4kbvgU5YTNr/JR5lnBjQcBEqw2i72BHyBoqq3NEPsAB IUtO8g+gGzYt2Mm0zgbw7tvj0rts7imau4rBrFl426pdzUHdQjKa6deR7xZlrF9Uva hXgvkGUVazB+A== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id 94553CE09F5; Thu, 17 Jul 2025 09:04:00 -0700 (PDT) Date: Thu, 17 Jul 2025 09:04:00 -0700 From: "Paul E. McKenney" To: Steven Rostedt Cc: Alexei Starovoitov , Mathieu Desnoyers , Sebastian Andrzej Siewior , Boqun Feng , linux-rt-devel@lists.linux.dev, rcu@vger.kernel.org, linux-trace-kernel , Frederic Weisbecker , Joel Fernandes , Josh Triplett , Lai Jiangshan , Masami Hiramatsu , Neeraj Upadhyay , Thomas Gleixner , Uladzislau Rezki , Zqiang , bpf Subject: Re: [RFC PATCH 1/2] rcu: Add rcu_read_lock_notrace() Message-ID: <9fc968c0-214a-44eb-9f1c-06af4bbbb815@paulmck-laptop> Reply-To: paulmck@kernel.org References: <16dd7f3c-1c0f-4dfd-bfee-4c07ec844b72@paulmck-laptop> <20250716110922.0dadc4ec@batman.local.home> <895b48bd-d51e-4439-b5e0-0cddcc17a142@paulmck-laptop> <20250717111216.4949063d@batman.local.home> <20250717114028.77ea7745@batman.local.home> <20250717115510.7717f839@batman.local.home> Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250717115510.7717f839@batman.local.home> On Thu, Jul 17, 2025 at 11:55:10AM -0400, Steven Rostedt wrote: > On Thu, 17 Jul 2025 11:40:28 -0400 > Steven Rostedt wrote: > > > Yes, it is a tracepoint infra problem that we are trying to solve. The > > reason we are trying to solve it is because BPF programs can extend the > > time a tracepoint takes. If anything else extended the time, this would > > need to be solved as well. But currently it's only BPF programs that > > cause the issue. > > BTW, if we can't solve this issue and something else came along and > attached to tracepoints that caused unbounded latency, I would also > argue that whatever came along would need to be prevented from being > configured with PREEMPT_RT. My comment wasn't a strike against BPF > programs; It was a strike against something adding unbounded latency > into a critical section that has preemption disabled. I would imagine that many PREEMPT_RT installations would have a severe and heavy-weight review, test, and approval process for BPF programs intended for use in production systems... Thanx, Paul