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=-7.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 98CD6C433DF for ; Wed, 5 Aug 2020 08:41:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7ADD022B40 for ; Wed, 5 Aug 2020 08:41:06 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="YpfDa2hQ" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728094AbgHEIlF (ORCPT ); Wed, 5 Aug 2020 04:41:05 -0400 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:43279 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726841AbgHEIk7 (ORCPT ); Wed, 5 Aug 2020 04:40:59 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1596616857; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=vCqdC0QayVIHiEIjRosykAcabVSJOwH5cXt4Ri7q9RA=; b=YpfDa2hQ+5zfc8qcE5yHRIOyPrUS97cj+JxuqFIfblUzMEo1jZRhjEJASo6hHxVcc/4dqK QmXOkZwiesartzHFsOSBfvJ7T1aG11ME3e57tbJRlQe/QFUKlb/y3+5wb/Dlx579BwIFo6 LlUC8aVN3+g0GvDlgkcj+TskFd7WJq4= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-18-JLox6VvKNkWfmobMcNlDaQ-1; Wed, 05 Aug 2020 04:40:52 -0400 X-MC-Unique: JLox6VvKNkWfmobMcNlDaQ-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 943A8106B243; Wed, 5 Aug 2020 08:40:50 +0000 (UTC) Received: from T590 (ovpn-13-169.pek2.redhat.com [10.72.13.169]) by smtp.corp.redhat.com (Postfix) with ESMTPS id C82655DA6A; Wed, 5 Aug 2020 08:40:37 +0000 (UTC) Date: Wed, 5 Aug 2020 16:40:31 +0800 From: Ming Lei To: Kashyap Desai Cc: John Garry , axboe@kernel.dk, jejb@linux.ibm.com, martin.petersen@oracle.com, don.brace@microsemi.com, Sumit Saxena , bvanassche@acm.org, hare@suse.com, hch@lst.de, Shivasharan Srikanteshwara , linux-block@vger.kernel.org, linux-scsi@vger.kernel.org, esc.storagedev@microsemi.com, chenxiang66@hisilicon.com, "PDL,MEGARAIDLINUX" Subject: Re: [PATCH RFC v7 10/12] megaraid_sas: switch fusion adapters to MQ Message-ID: <20200805084031.GA1995289@T590> References: <20200723140758.GA957464@T590> <20200724024704.GB957464@T590> <6531e06c-9ce2-73e6-46fc-8e97400f07b2@huawei.com> <20200728084511.GA1326626@T590> <965cf22eea98c00618570da8424d0d94@mail.gmail.com> <20200729153648.GA1698748@T590> <7f94eaf2318cc26ceb64bde88d59d5e2@mail.gmail.com> <20200804083625.GA1958244@T590> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Sender: linux-scsi-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-scsi@vger.kernel.org On Tue, Aug 04, 2020 at 02:57:52PM +0530, Kashyap Desai wrote: > > > > > > > However, it looks a bit > > > > complicated, and I was thinking if one simpler approach can be > > > > figured > > > out. > > > > > > I was thinking your original approach is simple, but if you think some > > > other simple approach I can test as part of these series. > > > BTW, I am still not getting why you think your original approach is > > > not good design. > > > > It is still not straightforward enough or simple enough for proving its > > correctness, even though the implementation isn't complicated. > > Ming - > > I noted your comments. > > I have completed testing and this particular latest performance issue on > Volume is outstanding. > Currently it is 20-25% performance drop in IOPs and we want that to be > closed before shared host tag is enabled for driver. > Just for my understanding - What will be the next steps on this ? > > I can validate any new approach/patch for this issue. > Hello, What do you think of the following patch? diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c index c866a4f33871..49f0fc5c7a63 100644 --- a/drivers/scsi/scsi_lib.c +++ b/drivers/scsi/scsi_lib.c @@ -552,8 +552,24 @@ static void scsi_run_queue_async(struct scsi_device *sdev) if (scsi_target(sdev)->single_lun || !list_empty(&sdev->host->starved_list)) kblockd_schedule_work(&sdev->requeue_work); - else - blk_mq_run_hw_queues(sdev->request_queue, true); + else { + /* + * smp_mb() implied in either rq->end_io or blk_mq_free_request + * is for ordering writing .device_busy in scsi_device_unbusy() + * and reading sdev->restarts. + */ + int old = atomic_read(&sdev->restarts); + + if (old) { + blk_mq_run_hw_queues(sdev->request_queue, true); + + /* + * ->restarts has to be kept as non-zero if there is + * new budget contention comes. + */ + atomic_cmpxchg(&sdev->restarts, old, 0); + } + } } /* Returns false when no more bytes to process, true if there are more */ @@ -1612,8 +1628,34 @@ static void scsi_mq_put_budget(struct request_queue *q) static bool scsi_mq_get_budget(struct request_queue *q) { struct scsi_device *sdev = q->queuedata; + int ret = scsi_dev_queue_ready(q, sdev); - return scsi_dev_queue_ready(q, sdev); + if (ret) + return true; + + /* + * If all in-flight requests originated from this LUN are completed + * before setting .restarts, sdev->device_busy will be observed as + * zero, then blk_mq_delay_run_hw_queue() will dispatch this request + * soon. Otherwise, completion of one of these request will observe + * the .restarts flag, and the request queue will be run for handling + * this request, see scsi_end_request(). + */ + atomic_inc(&sdev->restarts); + + /* + * Order writing .restarts and reading .device_busy, and make sure + * .restarts is visible to scsi_end_request(). Its pair is implied by + * __blk_mq_end_request() in scsi_end_request() for ordering + * writing .device_busy in scsi_device_unbusy() and reading .restarts. + * + */ + smp_mb__after_atomic(); + + if (unlikely(atomic_read(&sdev->device_busy) == 0 && + !scsi_device_blocked(sdev))) + blk_mq_delay_run_hw_queues(sdev->request_queue, SCSI_QUEUE_DELAY); + return false; } static blk_status_t scsi_queue_rq(struct blk_mq_hw_ctx *hctx, diff --git a/include/scsi/scsi_device.h b/include/scsi/scsi_device.h index bc5909033d13..1a5c9a3df6d6 100644 --- a/include/scsi/scsi_device.h +++ b/include/scsi/scsi_device.h @@ -109,6 +109,7 @@ struct scsi_device { atomic_t device_busy; /* commands actually active on LLDD */ atomic_t device_blocked; /* Device returned QUEUE_FULL. */ + atomic_t restarts; spinlock_t list_lock; struct list_head starved_entry; unsigned short queue_depth; /* How deep of a queue we want */ Thanks, Ming