From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-oo1-f52.google.com (mail-oo1-f52.google.com [209.85.161.52]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A4FE1249EC for ; Wed, 17 Jan 2024 19:42:33 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.161.52 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1705520555; cv=none; b=fNYGyCXBFMu9PcmNX4Qe4VEDSB8mTLcbJBa2nJ4sfnXP6p4dM/lf60TcYY7eaCF8b4S5JYa7jfEGL7rSLhiQlrl48dZzZorXknMn4N0OgZwBAzlgy2WDJtbXTLiG5RcwPzYCA0L16MUizj2Yf9Ha+1VXZ2qVYTrg1Lnr3TI1AXM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1705520555; c=relaxed/simple; bh=nHukp7ABSGZgox+voQNgZSwLeGnZqG7L9T1fJ25Rnh4=; h=Received:DKIM-Signature:X-Google-DKIM-Signature: X-Gm-Message-State:X-Google-Smtp-Source:X-Received:Received:Sender: Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=BTVrZRnKCXBvYN6q/EqLzclncM2KIzwedOMXGl3ARevTF7PlQnwfekvJDPqLTXd3anT3sHe4oz5rFzijQrBprgVZmpArdpgd9S4Xf182OMCPKu+1PQ0nsNhb9j82yKnGnuzxu3dEr29hGLOegezbm/PrcQ4vsJkGrfxBwWR8kwI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=Gvqs+3t8; arc=none smtp.client-ip=209.85.161.52 Authentication-Results: smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="Gvqs+3t8" Received: by mail-oo1-f52.google.com with SMTP id 006d021491bc7-598a5448ef5so4424332eaf.0 for ; Wed, 17 Jan 2024 11:42:33 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1705520552; x=1706125352; darn=vger.kernel.org; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:sender:from:to:cc:subject:date:message-id :reply-to; bh=ViFOzshsdI0neEHKP5+T/Kud83KXCwEJkLxP8fjCi9Y=; b=Gvqs+3t83Iqq3QEuKfbnRb40FuzSM1nYmFdltCkNUGLD/SHChh8ygtL7eDhGJQC4F0 /V2lp4TnFx3wHqkfNb5uF1fEjPzXJku2LFTfKycPpCA0OkPZY3L1OlN699tRrd5iVsJD ldv5N3RdVPVw4nnuqmdApEqbLcTHxEohRzzPq7RLetFpRQgTZOgODNnkHjNSoj/SclwS sMntLH6qmCGa4nFB7gj+wBm8fT5J6NXGT4KlKR4H6lCRGIjDJOgtkixnVdM/SEfBxj4H KHugDJOpe36vm2zyUL4M22NuwLtma8c37N8RfI0RDNN2oOrltI6T9uFttRkYyAvljGRH t2JA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1705520552; x=1706125352; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:sender:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=ViFOzshsdI0neEHKP5+T/Kud83KXCwEJkLxP8fjCi9Y=; b=gbZlRTGjuzPYifnTw2i7Loxm4HTqORoFdyoEjMQ7NGUQFjMFuvqDhjlBfvzT+KVL4l t0MNX5zXb9mSJ4HD12mQz+QJTEWDobt6YGyCwEojM4uYGFSuVHc/C279y+SUQWNObqIJ QM3nxPzETYRQUwD54Bmw4LQfXQ45jpDXo/OFVEc52/0lQGUlzdH2OU6sORBdf8rRb/PH +B4n7T8kdyIvUuJ4n4S17anS/Q+pLVITdr6pDEkOF3y0TNoYQNb10SPdxE9AnnmpZGR3 +71UrapMHAKXik/o+FR9MlfgArfQJJ59eziHNWJZxdtaqABWLW0dWQsDVrgpovHR2pCK GPFQ== X-Gm-Message-State: AOJu0YxdoABlUFMdjpx3Ow7ECv6gbTlIlXN44Hxz731TOas29mV/qg2r SIroo0Awn6lblKeyFsChFS4= X-Google-Smtp-Source: AGHT+IEkZ6A0SVWHrplsXqg9e1EHz1I2sQTfnYGourX2+NwbKELbeBuu8qDYTs4RHTAymlGeMVEsJA== X-Received: by 2002:a05:6358:9b47:b0:175:bfd4:8d6c with SMTP id k7-20020a0563589b4700b00175bfd48d6cmr11587810rwa.40.1705520552496; Wed, 17 Jan 2024 11:42:32 -0800 (PST) Received: from localhost (dhcp-72-235-13-140.hawaiiantel.net. [72.235.13.140]) by smtp.gmail.com with ESMTPSA id w26-20020aa7859a000000b006dad993d91csm1821882pfn.129.2024.01.17.11.42.31 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 17 Jan 2024 11:42:32 -0800 (PST) Sender: Tejun Heo Date: Wed, 17 Jan 2024 09:42:31 -1000 From: Tejun Heo To: Waiman Long Cc: Juri Lelli , Lai Jiangshan , Aaron Tomlin , Valentin Schneider , linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH 3/4] kernel/workqueue: Distinguish between general unbound and WQ_SYSFS cpumask changes Message-ID: References: <20240116161929.232885-1-juri.lelli@redhat.com> <20240116161929.232885-4-juri.lelli@redhat.com> <72e4a971-96e5-44b7-b348-bbdb68e54b40@redhat.com> 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: <72e4a971-96e5-44b7-b348-bbdb68e54b40@redhat.com> Hello, On Wed, Jan 17, 2024 at 02:32:34PM -0500, Waiman Long wrote: > My impression is that changing the workqueue cpumask of ordered unbound > workqueue may break the ordering guarantee momentarily. I was planning to Ah, you're right. Changing cpumask would require changing the dfl_pwq and that can introduce extra concurrency and break ordering and it's exempt from unbound_cpumask updates. We likely need to add a mechanism for updating ordered wq's so that the new pwq doesn't become until the previous one is drained. Thanks. -- tejun