From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 0121D38C406 for ; Thu, 15 Oct 2026 15:27:25 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1792078051; cv=none; b=dGOu1w05s0Kq8xt7fl7ztgdPl5PwwGzn6p6ocSOCspxa0JlSZQ5KGy3f2UKT9QXfDmlOhcCdja6MKxrQ2IqLWGmk8s57mby5iO4KOMQGoqMhCvGSDWY60wV7Zw6aHXhxCkirI+NVoMeepNDoxUCWMM6lpgSfJbxDrHoqyvdyiZg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1792078051; c=relaxed/simple; bh=OGlCeNJVFRgwjLjG8L15yHP4bMx4gZHLfYSDqr+cMQI=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=nGvS4TvkzAQlMs7YWvVQD2kH63Sb3aJphWjJ0XSFmGEBzft0x5bvKJxjd6fhYpjJZ+0mWzEJr8cM2X/vPzWZBYfZCQ71cdxo9eqjzhKvEt7YGTlavyQgWb3XJ5ozLhMr2dnIKdsWhcwiK56+3fvACLbP5ag+W7NLIpaYX66NtGc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=MKgwjkGd; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="MKgwjkGd" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 111A61F000C4; Thu, 15 Oct 2026 15:27:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1792078045; bh=xNwVZrCUmYnYbmxcd6KpR2qXRydVQUugSp+/fto1+ss=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=MKgwjkGdxpakNjyfeCeIi3wpnQ99V4nl2dVO+7mkYeZwVpR1z75OJYqK0EjZcrxKF W6ClAY8VtiRqCW5QOPIRNlJq+cst7p5dGq3k39HvS7Rkpbf2L4jLNbSRmBvcS0UTv3 n4iEYbxn42XEQBzc0PG+/o/FKqX/58UhbT+zMCuC03IW7jznV//h5gJWss4PxKzju6 92gnIzi+RHtwqc0dOWVIv5FCalBPYOBNHKjEE2u6TY7FLBEdRDCyAHq8frA+Qoqk+a 3niZevR6aWQgF+umAebw1cqWbUgMmLKK9siLMZwaPEPCh/RcalfbEgbbt7nIPc5z9c yiemVnmP6vVgg== Date: Thu, 15 Oct 2026 10:27:24 -0500 From: Clark Williams To: "Paul E. McKenney" Cc: Sebastian Andrzej Siewior , Steven Rostedt , linux-rt-devel@lists.linux.dev Subject: Re: Possible enhancement to RCU CPU stall warning messages Message-ID: References: Precedence: bulk X-Mailing-List: linux-rt-devel@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Tue, Oct 13, 2026 at 05:41:41PM -0700, Paul E. McKenney wrote: > Hello! > > While chasing an "interesting" bug [1], I modified the RCU CPU > stall-warning code so that when a task (as opposed to a CPU) is > blocking the grace period due to being preempted, the stall-warning > message includes the task that is currently running on the CPU that the > preempted task wants to run on. (In the case of the "interesting" bug, > I kid you not, that CPU was idle.) > > Would this stall-warning addition be useful for PREEMPT_RT users? > > If it is not useful, I am going to keep it out of tree. Something about > it needing a way to dig into scheduler internals. ;-) > > But if you want it, please let me know. > > Thanx, Paul > > [1] https://lore.kernel.org/all/8fa7f795-518c-4507-b684-60b0c1cac2c5@paulmck-laptop/ > Paul, While RCU isn't one of the common reasons for a latency spike, if it *is*, then it's not one that's easily tracked down. For that reason I'm in favor of using your patch. That said, if it's going to be a pain to maintain, I can live without it. Clark