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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 18E32C001DF for ; Fri, 20 Oct 2023 16:46:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1377891AbjJTQp7 (ORCPT ); Fri, 20 Oct 2023 12:45:59 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50888 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1377885AbjJTQp6 (ORCPT ); Fri, 20 Oct 2023 12:45:58 -0400 Received: from mail-qk1-f169.google.com (mail-qk1-f169.google.com [209.85.222.169]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0FDB0197 for ; Fri, 20 Oct 2023 09:45:57 -0700 (PDT) Received: by mail-qk1-f169.google.com with SMTP id af79cd13be357-7789577b53fso59122185a.3 for ; Fri, 20 Oct 2023 09:45:57 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1697820356; x=1698425156; h=content-transfer-encoding:in-reply-to:from:references:cc:to :content-language:subject:user-agent:mime-version:date:message-id :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=T9PuSn2bB2IxGmknw6dB/Si6eiBpR7N2reEFrg6SRRw=; b=TvyXjQegWGkYpxZOUBTEIKc0IbgW0aETBXcecZp8rKOkKtrf8mFM2BkkPX+0vWgnhJ AxdY/pksUW/mcHkQHIApS8fQ9DH0Bzv2u5WMpQdOKL65TQ5RSVmCqHPJXE0KqdQh00ff JzuH7RlYLIWgOysRvW4yNG3S0o16CW1PyYlFYZDmqbjptZiUWTZv1YLiLayYwk+c+0sE Yjk5Y0zkUr2H3QLMMQajh2aPuJsSN5PkRPAaMbHRml/SQxDUx/fwPswoD0gMIIgbY8Z3 U9ajhzloEsYDDoXB4Tq182FqCVCpEcmWGAXJDhGaES88DQToQUJPV5pxnIVg6IJ2Q4GT WlLA== X-Gm-Message-State: AOJu0YyWWRsyRu8sa9fDDrhibB5n4vF60GqH9mhf/bBzUrK1ghnlXYWI qVvmHCPVYieZBz8pXp1lTzQ= X-Google-Smtp-Source: AGHT+IEJInSBruV0jfpzWfofWc1iRCzttLXdkFnZ7iVpoikJ5rWL5wnHg0VUGTK6J4ksoF2BghrPBQ== X-Received: by 2002:a05:620a:2995:b0:76a:ece7:2071 with SMTP id r21-20020a05620a299500b0076aece72071mr2700085qkp.41.1697820355932; Fri, 20 Oct 2023 09:45:55 -0700 (PDT) Received: from [192.168.104.176] ([64.245.0.218]) by smtp.gmail.com with ESMTPSA id o10-20020a05620a22ca00b0076cc4610d0asm738158qki.85.2023.10.20.09.45.54 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 20 Oct 2023 09:45:55 -0700 (PDT) Message-ID: Date: Fri, 20 Oct 2023 09:45:53 -0700 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] block: Improve shared tag set performance Content-Language: en-US To: Keith Busch Cc: Christoph Hellwig , Jens Axboe , linux-block@vger.kernel.org, "Martin K . Petersen" , Ming Lei , Damien Le Moal , Yu Kuai , Ed Tsai References: <20231018180056.2151711-1-bvanassche@acm.org> <20231020044159.GB11984@lst.de> <0d2dce2a-8e01-45d6-b61b-f76493d55863@acm.org> From: Bart Van Assche In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On 10/20/23 09:25, Keith Busch wrote: > The legacy block request layer didn't have a tag resource shared among > multiple request queues. Each queue had their own mempool for allocating > requests. The mempool, I think, would always guarantee everyone could > get at least one request. I think that the above is irrelevant in this context. As an example, SCSI devices have always shared a pool of tags across multiple logical units. This behavior has not been changed by the conversion of the SCSI core from the legacy block layer to blk-mq. For other (hardware) block devices it didn't matter either that there was no upper limit to the number of requests the legacy block layer could allocate. All hardware block devices I know support fixed size queues for queuing requests to the block device. Bart.