From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from 013.lax.mailroute.net (013.lax.mailroute.net [199.89.1.16]) (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 7601E21767A; Fri, 19 Dec 2025 17:35:20 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=199.89.1.16 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1766165722; cv=none; b=DhYAiMC9CEX0OfReq0eGu0Ja8lBltquwRTFI87BIakzXz9vWN2sb5n2EWMp+z/o2JP3AWT4zapbT7Rqg/0/N8SM42p/KTs4VN8zvvelubsGhhqX8IggkO9UL2zKh3p/7Uz7bLfUzhYgDCrFH9Dw7sojrSvI4dke/1gxVy3a9ksg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1766165722; c=relaxed/simple; bh=/UM1x9gOOEfFuA2M3GO2QtAGlimQ9fJx3lIfkmsUh6c=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=GzjKRFFMwyWLQDzX9x+gCX+Yl7QW2Ncj03UQ76dYB/v+Vm2xhOSw0eEROXVhiGx29ON2yCWRm+umV9xBLOLKxT8KQMF/Mx7XZu655MarRpyOCLwR+0MATr4lnkpdANnvOKY5q0LWb2x8hfv8x2R31SEGuJipMmmHvdBJDDRcuAQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=acm.org; spf=pass smtp.mailfrom=acm.org; dkim=pass (2048-bit key) header.d=acm.org header.i=@acm.org header.b=33yMuV2e; arc=none smtp.client-ip=199.89.1.16 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=acm.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=acm.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=acm.org header.i=@acm.org header.b="33yMuV2e" Received: from localhost (localhost [127.0.0.1]) by 013.lax.mailroute.net (Postfix) with ESMTP id 4dXvnN0Knpzlw8Yd; Fri, 19 Dec 2025 17:35:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=acm.org; h= content-transfer-encoding:content-type:content-type:in-reply-to :from:from:content-language:references:subject:subject :user-agent:mime-version:date:date:message-id:received:received; s=mr01; t=1766165718; x=1768757719; bh=Ed2pB4/DgHi2VX769DnyeGvx zCzvF9nTLPvZD+WqVp0=; b=33yMuV2ea1/x9ToTPu7YufGkqrV4byBGNiMInSf4 lD5HvKYJJxyh1NagcBJLtY6qDJe4egBDl+JjiYKnAZPLy0Qcj1yOYtSQaXlnpnhQ xxAf08nDqjfVxiik0taHT3xl3258L556z7nvIRzj6va0Z5Ny/tQhXmy5sIP4WkY9 lpAE3m0wTlSJ11pgtwHrSxPudN0eykDkFSi/A+pigUXNjbRR1/YjfPeoBvboXXBM VYmHIm0l8MWzOh2p4CiE7e0eXe+OC/59ky/iI6jcw5/CQnXMRuoyxyUlHgVSNrAF dGC1DsleoPAe/uISsIBSlRs/x/wGBw1tfTvAyc1aY3VUNA== X-Virus-Scanned: by MailRoute Received: from 013.lax.mailroute.net ([127.0.0.1]) by localhost (013.lax [127.0.0.1]) (mroute_mailscanner, port 10029) with LMTP id bOWTkcfrI2ef; Fri, 19 Dec 2025 17:35:18 +0000 (UTC) Received: from [100.119.48.131] (unknown [104.135.180.219]) (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) (Authenticated sender: bvanassche@acm.org) by 013.lax.mailroute.net (Postfix) with ESMTPSA id 4dXvnH4QTlzlvwpy; Fri, 19 Dec 2025 17:35:14 +0000 (UTC) Message-ID: Date: Fri, 19 Dec 2025 09:35:13 -0800 Precedence: bulk X-Mailing-List: linux-scsi@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 6/6] scsi: core: Improve IOPS in case of host-wide tags To: Damien Le Moal , "Martin K . Petersen" Cc: linux-scsi@vger.kernel.org, linux-block@vger.kernel.org, John Garry , Hannes Reinecke , Christoph Hellwig , Jens Axboe , Ming Lei , "James E.J. Bottomley" References: <20251216223052.350366-1-bvanassche@acm.org> <20251216223052.350366-7-bvanassche@acm.org> Content-Language: en-US From: Bart Van Assche In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 12/16/25 7:24 PM, Damien Le Moal wrote: > On 12/17/25 07:30, Bart Van Assche wrote: >> The SCSI core uses the budget map to restrict the number of commands >> that are in flight per logical unit. That limit check can be left out if >> host->cmd_per_lun >= host->can_queue and if the host tag set is shared >> across all hardware queues or if there is only one hardware queue Since > > Missing a period at the end of the sentence (before Since). But more > importantly, this does not explain why the above is true, and frankly, I do not > see it... Hi Damien, The purpose of the SCSI device budget map is to prevent that the queue depth limit for that SCSI device is exceeded. If there is only a single hardware queue or there is a host-wide tag set and host->cmd_per_lun is identical to host->can_queue, it is not possible that the queue depth for a single SCSI device is exceeded and hence the SCSI device budget map is not needed. Please help with reviewing the ATA patch in this series. Thanks, Bart.