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 C05AA4D7D5E for ; Mon, 19 Oct 2026 13:20:45 +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=1792416046; cv=none; b=SbE9sk9k60AVheRc5UraP/JUqztA+SjT7x0J2PJZ+OBWsZAriqlfHk7s3bY34fSkdCJMzn4Xs+xhifWpJ2cdj6OsbxsZb2ee0BPOUzAF+dvF81wK4eMyeEQEYCWMwFBVty7C0/97ard0KoxXM874EQJNi9IqkbyLJSuFfzsw9UM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1792416046; c=relaxed/simple; bh=Y84iBQWlpHiFtmfpXJElZZ2mZgBlnpwNYTXZe0Fyluc=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=I1kdMp88fSZtLSeV1vFRVLm6tteQP32TsETKcZ9yPNLy2zGj41DUowgYwHsN7/BhnEmP1gIuOECWCq/YsAa8wVbv8dmQn6QHVys2+xFEV5LrAFOUxO8+usS4XXqm9ZlH56RB+JtVy9+rrI17sKlrjxrFFb2HXICGyNk2E84anBk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=hGRFuQmI; 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="hGRFuQmI" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2F0E41F000C4; Mon, 19 Oct 2026 13:20:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1792416045; bh=aFz6tMDneRfAiax81gydkYDdf/QTvsFngF3Ua5uanvw=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=hGRFuQmIUndqJBu5VOqmBOhswg2ATuImrzNeYthILoeSTkYPNzASDT0ZRy3LSrTtm 4TgDnNpZ8MR41xO1eCrTiCsO89Kr/1O0MDb4xSVfye2fEEFYN4vYpPlFYObOKMzwo9 ZItQP4JkpzglGg0Xk7jrgLMs9J7FdP5LLnzhKbLK4bcT/pzsR81eClKOr8pkG/gxGV Feq65vaUB+IjVIrF3xbd37FR61vvLEJ/EYDw3+BRn8qJTerBtKpbc2GbChaSk6kFQW kH4KgRtQJ9Y3hZE8cU/QYMlp0yantjyxiVxJChUPKP5mezmwfn3394dklGDyQLT3Kv VU2mQ4vvHhsnQ== Date: Mon, 19 Oct 2026 08:20:44 -0500 From: Clark Williams To: wen.yang@linux.dev Cc: Sebastian Andrzej Siewior , Steven Rostedt , linux-rt-devel@lists.linux.dev Subject: Re: [PATCH 6.6-rt 0/5] net: Backport backlog-NAPI threads to resolve PREEMPT_RT softirq warning in SMP flush 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 Mon, Oct 19, 2026 at 02:15:22AM +0800, wen.yang@linux.dev wrote: > From: Wen Yang > > Backport backlog-NAPI threads to v6.6-rt-next first, as requested by > Sebastian and Clark, before following up with the v6.1-rt backport. > The base is 4c4970859022 (Linux 6.6.151-rt78-rc1). > > The existing RT workaround, 1f7514c9c75d ("net: Avoid the IPI to free the"), > redirects deferred skb cleanup to a worker but leaves RPS remote-backlog > scheduling on the function-call IPI path. In a fresh RT guest this still > triggers do_softirq_post_smp_call_flush() from idle queue flushing. > > The ten earlier NAPI/RPS prerequisites are already present in v6.6, so this > series reverts the workaround and backports the four upstream changes (all > in upstream v6.10) in dependency order. Backlog-NAPI threads replace the > RPS/defer function-call notifications; ordinary scheduler wakeup IPI traffic > can still occur. Two of the changes were previously backported to ordinary > 6.6.y and reverted (507692c05636, 5a530c8ead06) only because PREEMPT_RT is > absent there, not for a functional defect. > > Backport notes > -------------- > Only 3/5 needs context adaptations; they are listed in that patch's commit > message. The other four apply without context edits. Unlike v6.1, v6.6 keeps > WRITE_ONCE(napi->list_owner, ...) because the field already exists here. > > Verification > ------------ > Each of the five stages was replayed against the base snapshot and compiled > for net/core/dev.o and net/core/skbuff.o. The baseline and final RT/RPS > bzImages were built with byte-identical normalized configs using GCC 9.4.0, > with no compiler warnings or errors. > > Tests use virtme-ng 1.38, x86_64 QEMU/KVM, four vCPUs and 2 GiB memory: > > vng --run --cpus 4 --memory 2G \ > --qemu-opts='-machine accel=kvm' --exec 'bash