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 B3E9A29D26E; Wed, 10 Jun 2026 16:36:04 +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=1781109365; cv=none; b=tUslUKp1eqF9qdgLJnqFRIKAKyMTnjAM3yyPWX9eOwEAvBQrGi7AwwI1sa9V0JEWcdX3DvIX6fx9ibUuvOJgrUVcDAnTqg93LVDC0SQonKKzkK23fNZExqnmAx0j16XTIJ+JIVgqWlSjnrjsk6yFD42CwQY9sZlmxF7BIaKraCQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781109365; c=relaxed/simple; bh=Ub3aJDzQfV3ndDy3RlbrtoMFR4cZS0ws3oiDXOTKo58=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=l1YSoOPv65VP/yjqZGuI7ndP5S6BuJ+kmbmiTbPS8kcT4BWIfU60ToER5wywp/7rNa8+N4uN15iLmvR5Yv8di4JEGiTAjOX6zRRZRlbJwA68KcNn6BhANePT25C2Phsn1ZzhA0MG+kVQJjheW93jEywWawbyBpiyL81W8u7leP8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=dYINVrSZ; 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="dYINVrSZ" 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> Precedence: bulk X-Mailing-List: linux-hyperv@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: 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.