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 X-Spam-Level: X-Spam-Status: No, score=-15.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8E22EC433F5 for ; Fri, 24 Sep 2021 10:36:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6188A610CB for ; Fri, 24 Sep 2021 10:36:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240648AbhIXKhw (ORCPT ); Fri, 24 Sep 2021 06:37:52 -0400 Received: from frasgout.his.huawei.com ([185.176.79.56]:3874 "EHLO frasgout.his.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229495AbhIXKhw (ORCPT ); Fri, 24 Sep 2021 06:37:52 -0400 Received: from fraeml743-chm.china.huawei.com (unknown [172.18.147.206]) by frasgout.his.huawei.com (SkyGuard) with ESMTP id 4HG7g160XVz67NKf; Fri, 24 Sep 2021 18:33:49 +0800 (CST) Received: from lhreml724-chm.china.huawei.com (10.201.108.75) by fraeml743-chm.china.huawei.com (10.206.15.224) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2308.8; Fri, 24 Sep 2021 12:36:17 +0200 Received: from [10.47.86.252] (10.47.86.252) by lhreml724-chm.china.huawei.com (10.201.108.75) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256) id 15.1.2308.8; Fri, 24 Sep 2021 11:36:16 +0100 Subject: Re: [PATCH v4 12/13] blk-mq: Use shared tags for shared sbitmap support To: Hannes Reinecke , CC: , , , , Kashyap Desai References: <1632472110-244938-1-git-send-email-john.garry@huawei.com> <1632472110-244938-13-git-send-email-john.garry@huawei.com> <9dd771bb-9e45-ecd2-d8e4-93c6e9cb9b59@suse.de> From: John Garry Message-ID: <49947654-591f-c686-5908-7938ab653e6d@huawei.com> Date: Fri, 24 Sep 2021 11:39:28 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.12.1 MIME-Version: 1.0 In-Reply-To: <9dd771bb-9e45-ecd2-d8e4-93c6e9cb9b59@suse.de> Content-Type: text/plain; charset="utf-8"; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit X-Originating-IP: [10.47.86.252] X-ClientProxiedBy: lhreml701-chm.china.huawei.com (10.201.108.50) To lhreml724-chm.china.huawei.com (10.201.108.75) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org + Kashyap On 24/09/2021 11:23, Hannes Reinecke wrote: > On 9/24/21 10:28 AM, John Garry wrote: >> Currently we use separate sbitmap pairs and active_queues atomic_t for >> shared sbitmap support. >> >> However a full sets of static requests are used per HW queue, which is >> quite wasteful, considering that the total number of requests usable at >> any given time across all HW queues is limited by the shared sbitmap >> depth. >> >> As such, it is considerably more memory efficient in the case of shared >> sbitmap to allocate a set of static rqs per tag set or request queue, and >> not per HW queue. >> >> So replace the sbitmap pairs and active_queues atomic_t with a shared >> tags per tagset and request queue, which will hold a set of shared static >> rqs. >> >> Since there is now no valid HW queue index to be passed to the blk_mq_ops >> .init and .exit_request callbacks, pass an invalid index token. This >> changes the semantics of the APIs, such that the callback would need to >> validate the HW queue index before using it. Currently no user of shared >> sbitmap actually uses the HW queue index (as would be expected). >> >> Continue to use term "shared sbitmap" for now, as the meaning is known. >> >> Signed-off-by: John Garry >> --- >>   block/blk-mq-sched.c   | 82 ++++++++++++++++++------------------- >>   block/blk-mq-tag.c     | 61 ++++++++++------------------ >>   block/blk-mq-tag.h     |  6 +-- >>   block/blk-mq.c         | 91 +++++++++++++++++++++++------------------- >>   block/blk-mq.h         |  5 ++- >>   include/linux/blk-mq.h | 15 ++++--- >>   include/linux/blkdev.h |  3 +- >>   7 files changed, 125 insertions(+), 138 deletions(-) >> > The overall idea to keep the full request allocation per queue was to > ensure memory locality for the requests themselves. > When moving to a shared request structure we obviously loose that feature. > > But I'm not sure if that matters here; the performance impact might be > too small to be measurable, seeing that we'll be most likely bound by > hardware latencies anyway. > > Nevertheless: have you tested for performance regressions with this > patchset? I have tested relatively lower rates, like ~450K IOPS, without any noticeable regression. > I'm especially thinking of Kashyaps high-IOPS megaraid setup; if there > is a performance impact that'll be likely scenario where we can measure it. > I can test higher rates, like 2M IOPS, when I get access to the HW. @Kashyap, Any chance you can help test performance here? > But even if there is a performance impact this patchset might be > worthwhile, seeing that it'll reduce the memory footprint massively. Sure, I don't think that minor performance improvements can justify the excessive memory. Thanks, John