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 B860E3A7DF1; Tue, 20 Jan 2026 09:22:01 +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=1768900921; cv=none; b=O+RK+CwTu8VpFIPZ+BSEWJSmPUzZCfQlhYuRe+mfs9wbX/9AVPdTVwiBFBApP+f6w+NZUM/DRbqyDulXgluz9+FmpsEfYG2ZnGDPXU92iAtyxyAS/anWCKsFJw+Qn/lp4OjXxR6CVFRehg5iKbN7NGv/q+5iZE4lL6PizxBuYMk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768900921; c=relaxed/simple; bh=iAPNhBYIJLjx2YruUVpL11H29gOTfYcqJyhaw35nnAw=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=ThRZBqJR8fZ8IS9tcM+bMelb52BU0l1KOBjdTgj/SLVnoFsRRzBkkfyxOC4aXdXmQknKAYuCsgQg0awayqSTskrrwlxUaforlxVuHu/0T7KN5fFG0/VSOlS4xzud6SsLXBR1KnDMZzHOkDUkCfoJH6Xn8D9ula91ZPzfi9FM+9c= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=bcCKGA9D; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="bcCKGA9D" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 182EFC19424; Tue, 20 Jan 2026 09:22:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1768900921; bh=iAPNhBYIJLjx2YruUVpL11H29gOTfYcqJyhaw35nnAw=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=bcCKGA9DnHkK+CmpE5wssc9BlGWJBwiJ0vW3cJzeDYwLzfoG4UW9yQ4BgLlkakq9H ZV4DQ8H/YO54QHkFTtbmw5YSeJ2kzJvxkhkQaswgQlNX7c2PJvpsYhG6Aa4JdQH4Kg a5k851d0DyCu10L6rNwVRM9key34uHR28Bf+K/HI= Date: Tue, 20 Jan 2026 10:21:58 +0100 From: Greg Kroah-Hartman To: Sebastian Andrzej Siewior Cc: Jakub Kicinski , wen.yang@linux.dev, stable@vger.kernel.org, linux-kernel@vger.kernel.org, Paolo Abeni Subject: Re: [PATCH 6.6 3/3] net: Allow to use SMP threads for backlog NAPI. Message-ID: <2026012039-shuffle-apple-43ec@gregkh> References: <997bc0de4746100bb69e1bd2ccfb25315d8f62e4.1768751557.git.wen.yang@linux.dev> <20260119082534.1f705011@kernel.org> <20260119163026.aA1PeSmP@linutronix.de> <2026012040-unmolded-dreaded-6e06@gregkh> <20260120080104.0yYtfQR7@linutronix.de> 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: <20260120080104.0yYtfQR7@linutronix.de> On Tue, Jan 20, 2026 at 09:01:04AM +0100, Sebastian Andrzej Siewior wrote: > On 2026-01-20 07:03:58 [+0100], Greg Kroah-Hartman wrote: > > On Mon, Jan 19, 2026 at 05:30:26PM +0100, Sebastian Andrzej Siewior wrote: > > > On 2026-01-19 08:25:34 [-0800], Jakub Kicinski wrote: > > > > On Mon, 19 Jan 2026 00:15:46 +0800 wen.yang@linux.dev wrote: > > > > > From: Sebastian Andrzej Siewior > > > > > > > > > > commit dad6b97702639fba27a2bd3e986982ad6f0db3a7 upstream. > > > > > > > > > > Backlog NAPI is a per-CPU NAPI struct only (with no device behind it) > > > > > used by drivers which don't do NAPI them self, RPS and parts of the > > > > > stack which need to avoid recursive deadlocks while processing a packet. > > > > > > > > This is a rather large change to backport into LTS. > > > > > > I agree. While I saw these patches flying by, I don't remember a mail > > > where it was justified why it was needed. Did I miss it? > > > > Please see patch 0/3 in this series: > > https://lore.kernel.org/all/cover.1768751557.git.wen.yang@linux.dev/ > > The reasoning why this is needed is due to PREEMPT_RT. This targets v6.6 > and PREEMPT_RT is officially supported upstream since v6.12. For v6.6 > you still need the out-of-tree patch. This means not only select the > Kconfig symbol but also a bit futex, ptrace or printk. This queue does > not include the three patches here but has another workaround having > more or less the same effect. > > If this is needed only for PREEMPT_RT's sake I would suggest to route it > via the stable-rt instead and replace what is currently there. It's already merged, should this be reverted? I forgot RT was only for 6.12 and newer, sorry. greg k-h