From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.ozlabs.org (lists.ozlabs.org [112.213.38.117]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 752A1CD8CB2 for ; Wed, 10 Jun 2026 16:36:09 +0000 (UTC) Received: from boromir.ozlabs.org (localhost [127.0.0.1]) by lists.ozlabs.org (Postfix) with ESMTP id 4gbBHC6xGQz2yv2; Thu, 11 Jun 2026 02:36:07 +1000 (AEST) Authentication-Results: lists.ozlabs.org; arc=none smtp.remote-ip=172.234.252.31 ARC-Seal: i=1; a=rsa-sha256; d=lists.ozlabs.org; s=201707; t=1781109367; cv=none; b=CRds8efDW0F6oIhcJs8Fm++10tP7d1n0roUD/Nx5i6aWJVQ8llqEqwg1Incc1anyF/P3jlEseCWQnN8Fa+TIooqICRj3YAvnlgC6E5UhfrLFLug6RY0MLtd2d/4+NXeR9iYU09ivRTLpqpqbvaPvUXbPdgLjGcKB8VnT0jq5E2/86EEewX80C6ZNn5U/t1P5+WAGQfgYQVxyILoB2mLHHsl6qv1XWVLD93VGSxuSSEwl5WZcile+Ljsb4wQTFbU+0wtMtVbqcuur132zRP23tbVkt7FhFa9Lh0k9crpLoMNU4cJrhxP1LXEy7xo/k7KPQuKRaxHyAyoQTnSr9Pa3gA== ARC-Message-Signature: i=1; a=rsa-sha256; d=lists.ozlabs.org; s=201707; t=1781109367; c=relaxed/relaxed; bh=nh8wY943fEj9O68DsnnpwY2/V+toQvePmwkX7p5hMSw=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=i91mdnAP/YVgR/vY8II6DbGAQNeUL635Me2GLtUjSQCHzV6LD18yatrLnvtNNrUKaw1xTlFFtyzT371sPBt0pQYuL+aNglRmUaRjRNbhnL+EvXB36x6whIxEyGNV3HhCFjL5gwU4Tyl1bDhp0bCT9YGjiVVK68RIYZHpwdzOKQ8YiUV4kcMjIuYPEjONrdst4OhWnnMrcmRv8QIoCGRLyifItLgJieuUCyxiEyth3ZwqEpy87ndc9pLsMJ8rK+SBPAwZ9T3DjOlfpcMRUw9jGBJWi0e8ryoa9uqAoh5lsAKnSAafRrxFK0q7IRBp1FXUc/44XTildB3Vjy3xHyN9+g== ARC-Authentication-Results: i=1; lists.ozlabs.org; dmarc=pass (p=quarantine dis=none) header.from=kernel.org; dkim=pass (2048-bit key; unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=dYINVrSZ; dkim-atps=neutral; spf=pass (client-ip=172.234.252.31; helo=sea.source.kernel.org; envelope-from=kbusch@kernel.org; receiver=lists.ozlabs.org) smtp.mailfrom=kernel.org Authentication-Results: lists.ozlabs.org; dmarc=pass (p=quarantine dis=none) header.from=kernel.org Authentication-Results: lists.ozlabs.org; dkim=pass (2048-bit key; unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=dYINVrSZ; dkim-atps=neutral Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=kernel.org (client-ip=172.234.252.31; helo=sea.source.kernel.org; envelope-from=kbusch@kernel.org; receiver=lists.ozlabs.org) Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange x25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4gbBHB5bCvz2ysW for ; Thu, 11 Jun 2026 02:36:06 +1000 (AEST) Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id 6EF3743DF2; Wed, 10 Jun 2026 16:36:04 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id E40111F00893; Wed, 10 Jun 2026 16:36:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1781109364; bh=nh8wY943fEj9O68DsnnpwY2/V+toQvePmwkX7p5hMSw=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=dYINVrSZftHL1+14yqMRRxzqdHQ5Aru2hX4Xj5usxEkwHzPmZX+0xwOsW6Dztp5wP buvP2PuA+QV5xPj78OletWBvmwhb43jqvV5GFsrZnuZuAMghgSwQoh0S8sgN+S9BTm ixgW2hKOY1IFxC79EBrsQJFmBJhTgHzktayoDV1vYQ6PUatVZ8z/Tcr6XFUKU/a9/Z pheURjB4DZFygToELeoT3p6Kl+8pJ6zz/rbZLD4ZtWjHEo3RFM2sDUxPLErYC7D1UE E752J6xO3yZ8ppjwDDHNoD60M4V39r80G3RPynl7+S0nx3QFq8NW+mgS9cg+pAi3HA Rq8MlrT88sswQ== Date: Wed, 10 Jun 2026 10:35:59 -0600 From: Keith Busch To: Sumit Saxena Cc: Christoph Hellwig , "Martin K . Petersen" , Jens Axboe , "James E . J . Bottomley" , linux-scsi@vger.kernel.org, linux-block@vger.kernel.org, Adam Radford , Khalid Aziz , Adaptec OEM Raid Solutions , Matthew Wilcox , Hannes Reinecke , "Juergen E . Fischer" , Russell King , linux-arm-kernel@lists.infradead.org, Finn Thain , Michael Schmitz , Anil Gurumurthy , Sudarsana Kalluru , Oliver Neukum , Ali Akcaagac , Jamie Lenehan , Ram Vegesna , target-devel@vger.kernel.org, Bradley Grove , Satish Kharat , Sesidhar Baddela , Karan Tilak Kumar , Yihang Li , Don Brace , storagedev@microchip.com, HighPoint Linux Team , Tyrel Datwyler , Madhavan Srinivasan , Michael Ellerman , Nicholas Piggin , Christophe Leroy , linuxppc-dev@lists.ozlabs.org, Brian King , Lee Duncan , Chris Leech , Mike Christie , open-iscsi@googlegroups.com, Justin Tee , Paul Ely , Kashyap Desai , Shivasharan S , Chandrakanth Patil , megaraidlinux.pdl@broadcom.com, Sathya Prakash Veerichetty , Sreekanth Reddy , mpi3mr-linuxdrv.pdl@broadcom.com, Suganath Prabu Subramani , Ranjan Kumar , MPT-FusionLinux.pdl@broadcom.com, Daniel Palmer , GOTO Masanori , YOKOTA Hiroshi , Jack Wang , Geoff Levand , Michael Reed , Nilesh Javali , GR-QLogic-Storage-Upstream@marvell.com, Narsimhulu Musini , "K . Y . Srinivasan" , Haiyang Zhang , Wei Liu , Dexuan Cui , Long Li , linux-hyperv@vger.kernel.org, "Michael S . Tsirkin" , Jason Wang , Paolo Bonzini , Stefan Hajnoczi , Eugenio Perez , virtualization@lists.linux.dev, Vishal Bhakta , bcm-kernel-feedback-list@broadcom.com, Juergen Gross , Stefano Stabellini , Oleksandr Tyshchenko , xen-devel@lists.xenproject.org, Bart Van Assche Subject: Re: [PATCH v3 3/4] block: drop shared-tag fairness throttling Message-ID: References: <20260609121806.2121755-1-sumit.saxena@broadcom.com> <20260609121806.2121755-4-sumit.saxena@broadcom.com> X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , List-Unsubscribe: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Wed, Jun 10, 2026 at 09:16:11PM +0530, Sumit Saxena wrote: > The motivation for this change stems from performance issue we > encountered due to false sharing of the 'nr_active_requests_shared_tags' > counter > on certain CPU architectures. I initially submitted a patch to move that > counter to > its own cache line to avoid conflicts with 'nr_requests' and other hot > fields > (see: > https://patchwork.kernel.org/project/linux-scsi/patch/20260402074637.92417-3-sumit.saxena@broadcom.com/ > ). > > During the review, Bart shared his work, which eliminates the > counter entirely by removing the fairness throttling. My testing confirmed > that > this approach resolved the performance issues and improved IOPS. > This patch is part of a larger set, and I have reported the cumulative > performance > improvements in the cover letter. So the problem is just the atomic operation accounting overhead? I previously thought the device just really needed to consume all the tags to hit performance.