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 9E1C5325714; Tue, 3 Mar 2026 13:59:44 +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=1772546386; cv=none; b=aGEkTPcwGfYUkdOteDl5UVgivyQVGugQtjed2LyJgESPFEGClU00gDAWa3U9kTDR4hhwSpS1aJABRG3zr//iB5S75R8JxQzcABlmk0QLg3Idxm147PI4AtOQBw4UNVS368/hdPG3SVE0joaodQnvDfW5Mt5oVJJ0Se+ZE30Ka+w= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772546386; c=relaxed/simple; bh=jKaus7JILQepyWCXwKnvhBQxb+z701P4h/Do5wnO/M8=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=Vu98RTElnaIvlPSGDnGzYDC71tni7zYQJXPXJg1B64vYfkraYK+1JfDi/vQC9aUylIl/mjfkeDMdiwPMHm1ZJAbu7L8xcrCCL0SCQQHdXGOllQhUzdQ4nVts9VQRq+JlA3DanmIALnDeqFQiOLgE5v2DdACnmvCZPCsvrF2SLDg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=debian.org; spf=none smtp.mailfrom=debian.org; dkim=pass (2048-bit key) header.d=debian.org header.i=@debian.org header.b=O4vH8Htb; arc=none smtp.client-ip=82.195.75.108 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=debian.org Authentication-Results: smtp.subspace.kernel.org; spf=none 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="O4vH8Htb" 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-Transfer-Encoding: Content-Type:MIME-Version:References:Message-ID:Subject:Cc:To:From:Date: Reply-To:Content-ID:Content-Description; bh=ySs4CGpikBsJKutl/8s682ix5maGPGGOdKHXq1NQ/FY=; b=O4vH8HtbMvu9hyCi4MYtaIDLRT 4sZXEW12ZY4FGrG5H+rZJZITXbipiu7XwcRhQzFykr6QPh8+YPXhJ9AT8CInC3ryEZxZwd7OdoY7g q87PeNe/2CKNQDF8IqS5JRMsLjKHbSHuGsrhe8l4N6bB5/ZJjRHD8x+Y0fuD13YP9dC0ytqorCPMO /y9UUHs37fQUj17csz3YnLzMG04ro+UNWAc6BNh99tga3I7yijTAGk+DaRZZKgZap7LVp65gYZ400 5njipZW4Ow081sjxIV5ZfImxLnFcFp+G/MrKz5cYUMiGdY8Xplh0RLD5IDIPpGNiAbwr/iup34lLw 3Qz8BQWA==; Received: from authenticated user by stravinsky.debian.org with esmtpsa (TLS1.3:ECDHE_X25519__RSA_PSS_RSAE_SHA256__AES_256_GCM:256) (Exim 4.94.2) (envelope-from ) id 1vxQHj-00FEMf-5D; Tue, 03 Mar 2026 13:59:39 +0000 Date: Tue, 3 Mar 2026 05:59:29 -0800 From: Breno Leitao To: Michal =?utf-8?Q?Koutn=C3=BD?= Cc: Jens Axboe , Tejun Heo , Josef Bacik , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, thevlad@meta.com, kernel-team@meta.com Subject: Re: [PATCH] blk-cgroup: add CONFIG_BLK_CGROUP_DEBUG_STATS option Message-ID: References: <20260204-blk_cgroup_debug_stats-v1-1-09c0754b4242@debian.org> 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=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Debian-User: leitao hello Michal, First of all, sorry for being late here, I had some days off. On Thu, Feb 12, 2026 at 11:26:29AM +0100, Michal Koutný wrote: > On Wed, Feb 04, 2026 at 08:15:12AM -0800, Breno Leitao wrote: > > Add a Kconfig option to enable blkcg_debug_stats by default at compile > > time. When CONFIG_BLK_CGROUP_DEBUG_STATS is enabled, additional debugging > > information is shown in the cgroup io.stat file, including cost.wait, > > cost.indebt, and cost.indelay for iocost, as well as latency statistics > > for iolatency. > > This seems to be toggleable quite easily anytime at runtime (not sysctl > but modprobe config), not a boot cmdline where CONFIG_ default could > step in. > > This only guards printing of already collected stats (sometimes even > without kernel consumers), not sure if it's that useful. > > blk-cgroup isn't modularized since 32e380aedc3de ("blkcg: make > CONFIG_BLK_CGROUP bool") v3.5-rc1~42^2~92 exposing it like a module > parameter is historical artifact. > > So I'd dare to propose removing it altogether and print those stats > everytime. Readers of the nested-keys format should survive that. > (I don't even see the param documented.) > > And if there were eager readers that'd be affected performance-wise, > more conventional would be to make this only boot cmdline parameter that > could static-branch also the stat collection spots (for some more > benefit). And then would also a CONFIG_urable default make sense. > > WDYT? That seems to make sense and it also simplify kernel management. I am sending a V2 with it, let's see if there is any other concern.