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=-17.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 E1525C4332F for ; Fri, 24 Sep 2021 10:23:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CAC0D61164 for ; Fri, 24 Sep 2021 10:23:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241405AbhIXKZa (ORCPT ); Fri, 24 Sep 2021 06:25:30 -0400 Received: from smtp-out1.suse.de ([195.135.220.28]:35968 "EHLO smtp-out1.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S240310AbhIXKZ3 (ORCPT ); Fri, 24 Sep 2021 06:25:29 -0400 Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out1.suse.de (Postfix) with ESMTPS id 3117222428; Fri, 24 Sep 2021 10:23:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_rsa; t=1632479035; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=cdj+MChX4WpMa83LUp1k/Esc7Eco7Cg2FeFEGab5+Ek=; b=pv2YhabYU/ytTd6fBQH7+j4RkgAtmgFmNovZGGs/+P36zRZwVqjrJBktgV4POBQ12oYZzx 4N/jiMGIKPNCunjG3Nk6BDfd/loRPqRDo9ei426Xx0CU+R24/ABucJ3RcR5DGCw+Czb9Zw OzXRkMwb3kOD6neRWn7EyfiL5gaVQ4E= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1632479035; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=cdj+MChX4WpMa83LUp1k/Esc7Eco7Cg2FeFEGab5+Ek=; b=6NUJqaIS7y8JdVBp6wmwnzYXCVi5O0aNUJB644YMQLY/T+EtDHvwzLAXLTbQ1RaMhmEAxb XwSscH6gaWUH6tBw== Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id 06D4313AB5; Fri, 24 Sep 2021 10:23:55 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id 0xGDADunTWEGTwAAMHmgww (envelope-from ); Fri, 24 Sep 2021 10:23:55 +0000 Subject: Re: [PATCH v4 12/13] blk-mq: Use shared tags for shared sbitmap support To: John Garry , axboe@kernel.dk Cc: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-scsi@vger.kernel.org, ming.lei@redhat.com References: <1632472110-244938-1-git-send-email-john.garry@huawei.com> <1632472110-244938-13-git-send-email-john.garry@huawei.com> From: Hannes Reinecke Message-ID: <9dd771bb-9e45-ecd2-d8e4-93c6e9cb9b59@suse.de> Date: Fri, 24 Sep 2021 12:23:54 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.12.0 MIME-Version: 1.0 In-Reply-To: <1632472110-244938-13-git-send-email-john.garry@huawei.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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'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. But even if there is a performance impact this patchset might be worthwhile, seeing that it'll reduce the memory footprint massively. Cheers, Hannes -- Dr. Hannes Reinecke Kernel Storage Architect hare@suse.de +49 911 74053 688 SUSE Software Solutions GmbH, Maxfeldstr. 5, 90409 Nürnberg HRB 36809 (AG Nürnberg), Geschäftsführer: Felix Imendörffer