From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from stravinsky.debian.org (stravinsky.debian.org [82.195.75.108]) (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 6B1AE30EF77; Wed, 12 Aug 2026 09:28:22 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=82.195.75.108 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786526904; cv=none; b=AYRHdgoHU+3GY3gtz87biuGYRzBTqHpvbHqN5bWQWLhkZ23jKWPVTYmp4QL6BtKJ7imkqmNMesxk4FWJp/mQ2YSaftzCjOI9EOtB8XzWmd9hNUakhZwugTtifM1+SGbDKSYuh1AgVll/2Y7KdTOd26jAJIAC7zEERv63M5nS3Hs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786526904; c=relaxed/simple; bh=SK4MPPOum5/xEb7ZtlABlunA/xhLveYIyZcRf8TwA7Q=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=crtVHQrC/7K9XdetNxvckpYKyUpseJ5jkRckNXvcO+WdcUIfYZDP/1a/0k4hyK1UjMhLhA7UnERaxgtc6H5QbFumZnmXI//XkF9bmOje8A5HvHOpPMi6RrAMZ8qiOJ8vjp3Nv13er+gRj6FUP+pemGh1s0P1e8JIWrcP4/FmQ/E= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=debian.org; spf=pass smtp.mailfrom=debian.org; dkim=pass (2048-bit key) header.d=debian.org header.i=@debian.org header.b=lOUVxZUP; arc=none smtp.client-ip=82.195.75.108 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=debian.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=debian.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=debian.org header.i=@debian.org header.b="lOUVxZUP" 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=YUU7A/3S+/I5gW+NMIkmvowBgYiANelkV9JSudmJ3AQ=; b=lOUVxZUPZqLdhuVc7oRjr7bMIn dWoVui8YHVsx2e3f/rqm48PK6mDbVUCQRMluULhzTDVDuLWG0uw486P9Dl0zpPjyudSyaHZfoKIG1 KQ3kx7Ngo7h6ULPLQj0n+jNOTdI6TGYCYR1ysgXQOnxoStpWyx47vA84LRwAhWbwQ8IfuO+u4zyZH FjuSGgk09njhita9sp/CsWsLFQPIQBa73r1QLqvx4v5iqdABiOe35h+anicZLiOB7t4XgCwWc2Dof SQLYYfQ7uDON/zyGDExamhX34ykUsFN4EvA06bZOkURETvQcy/Md1bkzXWUnytGJmWkQfCJ+lyIqm oGtQ1E1Q==; 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 1wu5Fu-004F3B-25; Wed, 12 Aug 2026 09:28:14 +0000 Date: Wed, 12 Aug 2026 02:28:10 -0700 From: Breno Leitao To: "Paul E. McKenney" Cc: rcu@vger.kernel.org, linux-kernel@vger.kernel.org, David Dai Subject: Re: [PATCH RFC] rcu-tasks: Disable callback contend/collapse messages by default Message-ID: References: Precedence: bulk X-Mailing-List: linux-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: X-Debian-User: leitao On Tue, Aug 11, 2026 at 07:00:14PM -0700, Paul E. McKenney wrote: > New workloads can do large bursts of call_rcu_tasks() invocations in a > short time period, followed by a quiet time period long enough to drain > all of the callbacks, followed by another burst of call_rcu_tasks() > invocations. This can cause RCU Tasks to switch back and forth between > queuing callbacks only on CPU 0 (during quiet periods) and on all CPUs > (during bursts). > > Which is fine. Except for the fact that each cycle from CPU-0-only to > all-CPUs queuing and back generates three console messages, one announcing > the shift to all-CPUs queuing, another announcing the start of the shift > back to CPU-0-only queuing, and the third announcing completion of this > shift after an RCU grace period. And these console messages can overrun > console-log communications channels and obscure other console-message-based > debugging information. And the only known use for these console messages > is debugging RCU Tasks itself. > > This commit therefore adds a rcupdate.rcu_task_collapse_debug module > parameter that defaults to false (suppressing these console messages). > Those debugging or otherwise playing with RCU Tasks callback queuing > auto-adjustment can set this parameter to the value true. > > Reported-by: Breno Leitao > Reported-by: David Dai > Signed-off-by: Paul E. McKenney Reviewed-by: Breno Leitao Thanks for the patch. I confirm that this is flooding the monitoring systems at Meta, together with [1] Link: https://lore.kernel.org/all/20260810-swap-v1-0-375ef0767206@debian.org/ [0] > +static bool rcu_task_collapse_debug __read_mostly = false; nit: You don't need false here. Checkpatch even raises an error: ERROR: do not initialise statics to false Thanks! --breno