From patchwork Fri Sep 14 14:23:07 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Paolo Valente X-Patchwork-Id: 10600813 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id E93C513AD for ; Fri, 14 Sep 2018 14:23:31 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id C8E1F2B7E4 for ; Fri, 14 Sep 2018 14:23:31 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id BD4572B7E7; Fri, 14 Sep 2018 14:23:31 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.0 required=2.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,RCVD_IN_DNSWL_HI autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 401E42B7E4 for ; Fri, 14 Sep 2018 14:23:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728236AbeINTiJ (ORCPT ); Fri, 14 Sep 2018 15:38:09 -0400 Received: from mail-wr1-f65.google.com ([209.85.221.65]:39937 "EHLO mail-wr1-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727013AbeINTiF (ORCPT ); Fri, 14 Sep 2018 15:38:05 -0400 Received: by mail-wr1-f65.google.com with SMTP id n2-v6so10827085wrw.7 for ; Fri, 14 Sep 2018 07:23:20 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=from:to:cc:subject:date:message-id:in-reply-to:references; bh=rd8R49tSHe6GNNdxrka86f7ThsGMCBdbsdSM4u5ch9U=; b=BTmY+DOv8DiEIzGEBJX4RYWfTk/ZOXAwxG1eXFr6KPaJviJ3QBqi3DStYle0FMgmrL r7Ng47lpJf0ENMgzgGhvvVGCn3wy5zudPNNvoFs9PCymWb340uzsaMV6UN1y2JIakczL T7mbwvShfpS27whef0OAcbAhlzy+NF4PCSlJ0= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references; bh=rd8R49tSHe6GNNdxrka86f7ThsGMCBdbsdSM4u5ch9U=; b=SbubAOzgErZU0U2iPiJaunT/RAi41qlqxKPaDFoWi0OT7TmvAYWLM1KZD6BjBlafJa hn4SsCw+AmbFKNktp84E1Br2ob0181+b0w4Tjsxo1v4bp0W4QoTQJaJVKrQ2R6SWyHgy s5FXAlERl9KCU9C9HxiT22UoeHCGfiSH0dd8UYGL1Y1j61SDQXxY3CTcQmAw/UTkgCQv U1DBF/Q0a0okULp+rKxqtYtPbJTSAOTZNc4DLB3varwV70rFA8oWMkuH0g+k83amWhGd tsO2kYWB9kS/8pzJKxAsFKpcl/RIxputEHsyTWBv54uUYJ8p/guR3BGxw61fhGo3VrQb 6IOw== X-Gm-Message-State: APzg51AFA0BkXX7ctUmtwj0opqmtHCrIy6ZqD2Xox9YKc5gPOLxSfall W8nNXB+DnY8s29uxdU3tES+VaA== X-Google-Smtp-Source: ANB0VdbdvCYfqVSOb/n095syJgDLiAb80BBu3l5VK+nz6XsDsdv+qNW0FGKL0q6HbdONu2+kbhuwFg== X-Received: by 2002:a5d:448d:: with SMTP id j13-v6mr10052504wrq.236.1536934999666; Fri, 14 Sep 2018 07:23:19 -0700 (PDT) Received: from wifi-122_dhcprange-84.wifi.unimo.it (wifi-122_dhcprange-84.wifi.unimo.it. [155.185.122.84]) by smtp.gmail.com with ESMTPSA id k35-v6sm17084888wrc.14.2018.09.14.07.23.18 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 14 Sep 2018 07:23:18 -0700 (PDT) From: Paolo Valente To: Jens Axboe Cc: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, ulf.hansson@linaro.org, linus.walleij@linaro.org, broonie@kernel.org, bfq-iosched@googlegroups.com, oleksandr@natalenko.name, Paolo Valente Subject: [PATCH BUGFIX/IMPROVEMENT 1/3] block, bfq: correctly charge and reset entity service in all cases Date: Fri, 14 Sep 2018 16:23:07 +0200 Message-Id: <20180914142309.6789-2-paolo.valente@linaro.org> X-Mailer: git-send-email 2.16.1 In-Reply-To: <20180914142309.6789-1-paolo.valente@linaro.org> References: <20180914142309.6789-1-paolo.valente@linaro.org> Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP BFQ schedules entities (which represent either per-process queues or groups of queues) as a function of their timestamps. In particular, as a function of their (virtual) finish times. The finish time of an entity is computed as a function of the budget assigned to the entity, assuming, tentatively, that the entity, once in service, will receive an amount of service equal to its budget. Then, when the entity is expired because it finishes to be served, this finish time is updated as a function of the actual service received by the entity. This allows the entity to be correctly charged with only the service received, and then to be correctly re-scheduled. Yet an entity may receive service also while not being the entity in service (in the scheduling environment of its parent entity), for several reasons. If the entity remains with no backlog while receiving this 'unofficial' service, then it is expired. Also on such an expiration, the finish time of the entity should be updated to account for only the service actually received by the entity. Unfortunately, such an update is not performed for an entity expiring without being the entity in service. In a similar vein, the service counter of the entity in service is reset when the entity is expired, to be ready to be used for next service cycle. This reset too should be performed also in case an entity is expired because it remains empty after receiving service while not being the entity in service. But in this case the reset is not performed. This commit performs the above update of the finish time and reset of the service received, also for an entity expiring while not being the entity in service. Signed-off-by: Paolo Valente --- block/bfq-wf2q.c | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-) diff --git a/block/bfq-wf2q.c b/block/bfq-wf2q.c index ae52bff43ce4..ff7c2d470bb8 100644 --- a/block/bfq-wf2q.c +++ b/block/bfq-wf2q.c @@ -1181,10 +1181,17 @@ bool __bfq_deactivate_entity(struct bfq_entity *entity, bool ins_into_idle_tree) st = bfq_entity_service_tree(entity); is_in_service = entity == sd->in_service_entity; - if (is_in_service) { - bfq_calc_finish(entity, entity->service); + bfq_calc_finish(entity, entity->service); + + if (is_in_service) sd->in_service_entity = NULL; - } + else + /* + * Non in-service entity: nobody will take care of + * resetting its service counter on expiration. Do it + * now. + */ + entity->service = 0; if (entity->tree == &st->active) bfq_active_extract(st, entity); From patchwork Fri Sep 14 14:23:08 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Paolo Valente X-Patchwork-Id: 10600817 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 9106615A7 for ; Fri, 14 Sep 2018 14:23:56 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 74AC22B7EC for ; Fri, 14 Sep 2018 14:23:56 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 68CA92B7FB; Fri, 14 Sep 2018 14:23:56 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.0 required=2.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,RCVD_IN_DNSWL_HI autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id B43C52B7F5 for ; Fri, 14 Sep 2018 14:23:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728237AbeINTiI (ORCPT ); Fri, 14 Sep 2018 15:38:08 -0400 Received: from mail-wm1-f66.google.com ([209.85.128.66]:54840 "EHLO mail-wm1-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728235AbeINTiI (ORCPT ); Fri, 14 Sep 2018 15:38:08 -0400 Received: by mail-wm1-f66.google.com with SMTP id c14-v6so2123488wmb.4 for ; Fri, 14 Sep 2018 07:23:22 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=from:to:cc:subject:date:message-id:in-reply-to:references; bh=M+kKZwDAbPtAP7Qkjv5tvIc/0u48iTxGHE2Zfoo1e6E=; b=T9VQZi1XlVk9k/P+MMtiy3GtXFT9jG4xtC0/Js2nTqEmmRdIAwUlx2gMBwVJqGFANH +XtZdbYYhV6NAR1EPEgPlTzI7dDsolyJOZPDoGAa9nBBbM0djwr3VGeSJudEVBQ2iH2I pAc0HGNEiZ/yst5qeay6jskTiZxS7qMh3O1K0= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references; bh=M+kKZwDAbPtAP7Qkjv5tvIc/0u48iTxGHE2Zfoo1e6E=; b=KGTCOODd2Wd5Z5CUJDyYUcWXA1CvxaXJZzPwUZcNRDy2sudcFd+bJI0BIx7pZbglAU nrE99h62VnWJOWh7p77n9DcsEUy9puFY5cmZrDOUkc6mE6mt4kTWBuwm2+470qV7yoSC mpm9/jxEmsECJzl02HwWuUz0QLO0k40i9SJ/CDKZmxdHlGG/K1+j0rUdamMhQD4U/N0S pFSO15xS1mOByR2//4SXzxI7zjLepRNrVffJBH7udfLiMqGq9uAeg9pIYgRwc5vIYv22 FOechfykeadQ9F88NZzmNk20bRzD64fvNg/hrJqgZq1IHCazLToNbqw+VHRxKjM1U182 4abg== X-Gm-Message-State: APzg51AFccnT12L0OInvU9mO7CbOrVPVAkIymNMxSZukTOXzKwj+LLDw 9uMhdhcPV/Yc1114D6rFXizyM9e0lDM= X-Google-Smtp-Source: ANB0Vdb2roS9vO2NnQduviZfwfeiGvCgLauMSgta6qZiF+WYb8jivgMQZBztG+rBV1UKoWSo3lQT2w== X-Received: by 2002:a1c:3712:: with SMTP id e18-v6mr2608332wma.84.1536935001094; Fri, 14 Sep 2018 07:23:21 -0700 (PDT) Received: from wifi-122_dhcprange-84.wifi.unimo.it (wifi-122_dhcprange-84.wifi.unimo.it. [155.185.122.84]) by smtp.gmail.com with ESMTPSA id k35-v6sm17084888wrc.14.2018.09.14.07.23.19 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 14 Sep 2018 07:23:20 -0700 (PDT) From: Paolo Valente To: Jens Axboe Cc: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, ulf.hansson@linaro.org, linus.walleij@linaro.org, broonie@kernel.org, bfq-iosched@googlegroups.com, oleksandr@natalenko.name, Paolo Valente Subject: [PATCH BUGFIX/IMPROVEMENT 2/3] block, bfq: inject other-queue I/O into seeky idle queues on NCQ flash Date: Fri, 14 Sep 2018 16:23:08 +0200 Message-Id: <20180914142309.6789-3-paolo.valente@linaro.org> X-Mailer: git-send-email 2.16.1 In-Reply-To: <20180914142309.6789-1-paolo.valente@linaro.org> References: <20180914142309.6789-1-paolo.valente@linaro.org> Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP The Achilles' heel of BFQ is its failing to reach a high throughput with sync random I/O on flash storage with internal queueing, in case the processes doing I/O have differentiated weights. The cause of this failure is as follows. If at least two processes do sync I/O, and have a different weight from each other, then BFQ plugs I/O dispatching every time one of these processes, while it is being served, remains temporarily without pending I/O requests. This plugging is necessary to guarantee that every process enjoys a bandwidth proportional to its weight; but it empties the internal queue(s) of the drive. And this kills throughput with random I/O. So, if some processes have differentiated weights and do both sync and random I/O, the end result is a throughput collapse. This commit tries to counter this problem by injecting the service of other processes, in a controlled way, while the process in service happens to have no I/O. This injection is performed only if the medium is non rotational and performs internal queueing, and the process in service does random I/O (service injection might be beneficial for sequential I/O too, we'll work on that). As an example of the benefits of this commit, on a PLEXTOR PX-256M5S SSD, and with five processes having differentiated weights and doing sync random 4KB I/O, this commit makes the throughput with bfq grow by 400%, from 25 to 100MB/s. This higher throughput is 10MB/s lower than that reached with none. As some less random I/O is added to the mix, the throughput becomes equal to or higher than that with none. This commit is a very first attempt to recover throughput without losing control, and certainly has many limitations. One is, e.g., that the processes whose service is injected are not chosen so as to distribute the extra bandwidth they receive in accordance to their weights. Thus there might be loss of weighted fairness in some cases. Anyway, this loss concerns extra service, which would not have been received at all without this commit. Other limitations and issues will probably show up with usage. Signed-off-by: Paolo Valente --- block/bfq-iosched.c | 68 ++++++++++++++++++++++++++++++++++++++++++++++++----- block/bfq-iosched.h | 26 ++++++++++++++++++++ 2 files changed, 88 insertions(+), 6 deletions(-) diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c index 653100fb719e..d94838bcc135 100644 --- a/block/bfq-iosched.c +++ b/block/bfq-iosched.c @@ -3182,6 +3182,13 @@ static unsigned long bfq_bfqq_softrt_next_start(struct bfq_data *bfqd, jiffies + nsecs_to_jiffies(bfqq->bfqd->bfq_slice_idle) + 4); } +static bool bfq_bfqq_injectable(struct bfq_queue *bfqq) +{ + return BFQQ_SEEKY(bfqq) && bfqq->wr_coeff == 1 && + blk_queue_nonrot(bfqq->bfqd->queue) && + bfqq->bfqd->hw_tag; +} + /** * bfq_bfqq_expire - expire a queue. * @bfqd: device owning the queue. @@ -3291,6 +3298,8 @@ void bfq_bfqq_expire(struct bfq_data *bfqd, if (ref == 1) /* bfqq is gone, no more actions on it */ return; + bfqq->injected_service = 0; + /* mark bfqq as waiting a request only if a bic still points to it */ if (!bfq_bfqq_busy(bfqq) && reason != BFQQE_BUDGET_TIMEOUT && @@ -3629,6 +3638,30 @@ static bool bfq_bfqq_must_idle(struct bfq_queue *bfqq) return RB_EMPTY_ROOT(&bfqq->sort_list) && bfq_better_to_idle(bfqq); } +static struct bfq_queue *bfq_choose_bfqq_for_injection(struct bfq_data *bfqd) +{ + struct bfq_queue *bfqq; + + /* + * A linear search; but, with a high probability, very few + * steps are needed to find a candidate queue, i.e., a queue + * with enough budget left for its next request. In fact: + * - BFQ dynamically updates the budget of every queue so as + * to accommodate the expected backlog of the queue; + * - if a queue gets all its requests dispatched as injected + * service, then the queue is removed from the active list + * (and re-added only if it gets new requests, but with + * enough budget for its new backlog). + */ + list_for_each_entry(bfqq, &bfqd->active_list, bfqq_list) + if (!RB_EMPTY_ROOT(&bfqq->sort_list) && + bfq_serv_to_charge(bfqq->next_rq, bfqq) <= + bfq_bfqq_budget_left(bfqq)) + return bfqq; + + return NULL; +} + /* * Select a queue for service. If we have a current queue in service, * check whether to continue servicing it, or retrieve and set a new one. @@ -3710,10 +3743,19 @@ static struct bfq_queue *bfq_select_queue(struct bfq_data *bfqd) * No requests pending. However, if the in-service queue is idling * for a new request, or has requests waiting for a completion and * may idle after their completion, then keep it anyway. + * + * Yet, to boost throughput, inject service from other queues if + * possible. */ if (bfq_bfqq_wait_request(bfqq) || (bfqq->dispatched != 0 && bfq_better_to_idle(bfqq))) { - bfqq = NULL; + if (bfq_bfqq_injectable(bfqq) && + bfqq->injected_service * bfqq->inject_coeff < + bfqq->entity.service * 10) + bfqq = bfq_choose_bfqq_for_injection(bfqd); + else + bfqq = NULL; + goto keep_queue; } @@ -3803,6 +3845,14 @@ static struct request *bfq_dispatch_rq_from_bfqq(struct bfq_data *bfqd, bfq_dispatch_remove(bfqd->queue, rq); + if (bfqq != bfqd->in_service_queue) { + if (likely(bfqd->in_service_queue)) + bfqd->in_service_queue->injected_service += + bfq_serv_to_charge(rq, bfqq); + + goto return_rq; + } + /* * If weight raising has to terminate for bfqq, then next * function causes an immediate update of bfqq's weight, @@ -3821,13 +3871,12 @@ static struct request *bfq_dispatch_rq_from_bfqq(struct bfq_data *bfqd, * belongs to CLASS_IDLE and other queues are waiting for * service. */ - if (bfqd->busy_queues > 1 && bfq_class_idle(bfqq)) - goto expire; - - return rq; + if (!(bfqd->busy_queues > 1 && bfq_class_idle(bfqq))) + goto return_rq; -expire: bfq_bfqq_expire(bfqd, bfqq, false, BFQQE_BUDGET_EXHAUSTED); + +return_rq: return rq; } @@ -4232,6 +4281,13 @@ static void bfq_init_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq, bfq_mark_bfqq_has_short_ttime(bfqq); bfq_mark_bfqq_sync(bfqq); bfq_mark_bfqq_just_created(bfqq); + /* + * Aggressively inject a lot of service: up to 90%. + * This coefficient remains constant during bfqq life, + * but this behavior might be changed, after enough + * testing and tuning. + */ + bfqq->inject_coeff = 1; } else bfq_clear_bfqq_sync(bfqq); diff --git a/block/bfq-iosched.h b/block/bfq-iosched.h index a8a2e5aca4d4..37d627afdc2e 100644 --- a/block/bfq-iosched.h +++ b/block/bfq-iosched.h @@ -351,6 +351,32 @@ struct bfq_queue { unsigned long split_time; /* time of last split */ unsigned long first_IO_time; /* time of first I/O for this queue */ + + /* max service rate measured so far */ + u32 max_service_rate; + /* + * Ratio between the service received by bfqq while it is in + * service, and the cumulative service (of requests of other + * queues) that may be injected while bfqq is empty but still + * in service. To increase precision, the coefficient is + * measured in tenths of unit. Here are some example of (1) + * ratios, (2) resulting percentages of service injected + * w.r.t. to the total service dispatched while bfqq is in + * service, and (3) corresponding values of the coefficient: + * 1 (50%) -> 10 + * 2 (33%) -> 20 + * 10 (9%) -> 100 + * 9.9 (9%) -> 99 + * 1.5 (40%) -> 15 + * 0.5 (66%) -> 5 + * 0.1 (90%) -> 1 + * + * So, if the coefficient is lower than 10, then + * injected service is more than bfqq service. + */ + unsigned int inject_coeff; + /* amount of service injected in current service slot */ + unsigned int injected_service; }; /** From patchwork Fri Sep 14 14:23:09 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Paolo Valente X-Patchwork-Id: 10600815 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 170B113AD for ; Fri, 14 Sep 2018 14:23:53 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id EF0F42B7EC for ; Fri, 14 Sep 2018 14:23:52 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id E35652B7F6; Fri, 14 Sep 2018 14:23:52 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.0 required=2.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,RCVD_IN_DNSWL_HI autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 82F862B7EC for ; Fri, 14 Sep 2018 14:23:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728251AbeINTiI (ORCPT ); Fri, 14 Sep 2018 15:38:08 -0400 Received: from mail-wm1-f66.google.com ([209.85.128.66]:37029 "EHLO mail-wm1-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728172AbeINTiH (ORCPT ); Fri, 14 Sep 2018 15:38:07 -0400 Received: by mail-wm1-f66.google.com with SMTP id n11-v6so2127806wmc.2 for ; Fri, 14 Sep 2018 07:23:23 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=from:to:cc:subject:date:message-id:in-reply-to:references; bh=NDz4sLfCSE+TqlBABM2X5T0yTWgA3O/WCAY/iJ5XldA=; b=YNVrodgCbk9Qq5HogJG1AhAKMGOgsPkDX58PZ3nUiWAS19J+GLmr3eM3hbVzJEl1Nn iM2s6VmpVn4WiFQuLfYRHP2pMDq8+L3ybI0QLjIYffvVskXBxpPjNaBX3+q4bXdcnVLY Du/pd6y5PG7r0qZeYTHjwoZW0jagutAO8C3+E= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references; bh=NDz4sLfCSE+TqlBABM2X5T0yTWgA3O/WCAY/iJ5XldA=; b=W3SjTR6Gumj59ac+vR1u7m85jGsS/2fYIWnHBpN76MFtsWlBnOuWKQUR9bXOGPUPDS K9+vOM6a1PuPhdTEGa3Zj9Q1QIXAwefcQhgeg/7w2u2VeV5h+LfbJI6YRhHxpBdrEjcX yBl7H3CPsdw1dp01UOtydui2g9UgBcdPeMiniNBFitypatu9pK5UNSgfOaRwzDj6la5b aWnCGZK16QWqNtHAgFzJ2bkHo+SnZdv1JDS59xm9Osk/br6LgwyQCTEVKGM8aguq+94+ KBeuR02UBzHNbmlY1ic5+XQyH1MPNSV5PYWENnkZq6NApwVbpfQrDVhM9u+Wd01jpxvc hADA== X-Gm-Message-State: APzg51BuGGhbfsj3qX5rhXqU0NJLXXCx4vYZKQwmdW9gsp+O8d4kKpJl N85p1gZmfTf15TfBNdy57pB/SA== X-Google-Smtp-Source: ANB0VdatT45JAM/5KjiNdu4KqJYvNk2u5kJbIkXjMdxryqHtWweyDmfxtS+Ji2yPHF7/9ddQxCFC+Q== X-Received: by 2002:a1c:c14:: with SMTP id 20-v6mr2618562wmm.117.1536935002644; Fri, 14 Sep 2018 07:23:22 -0700 (PDT) Received: from wifi-122_dhcprange-84.wifi.unimo.it (wifi-122_dhcprange-84.wifi.unimo.it. [155.185.122.84]) by smtp.gmail.com with ESMTPSA id k35-v6sm17084888wrc.14.2018.09.14.07.23.21 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 14 Sep 2018 07:23:21 -0700 (PDT) From: Paolo Valente To: Jens Axboe Cc: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, ulf.hansson@linaro.org, linus.walleij@linaro.org, broonie@kernel.org, bfq-iosched@googlegroups.com, oleksandr@natalenko.name, Paolo Valente Subject: [PATCH BUGFIX/IMPROVEMENT 3/3] blok, bfq: do not plug I/O if all queues are weight-raised Date: Fri, 14 Sep 2018 16:23:09 +0200 Message-Id: <20180914142309.6789-4-paolo.valente@linaro.org> X-Mailer: git-send-email 2.16.1 In-Reply-To: <20180914142309.6789-1-paolo.valente@linaro.org> References: <20180914142309.6789-1-paolo.valente@linaro.org> Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP To reduce latency for interactive and soft real-time applications, bfq privileges the bfq_queues containing the I/O of these applications. These privileged queues, referred-to as weight-raised queues, get a much higher share of the device throughput w.r.t. non-privileged queues. To preserve this higher share, the I/O of any non-weight-raised queue must be plugged whenever a sync weight-raised queue, while being served, remains temporarily empty. To attain this goal, bfq simply plugs any I/O (from any queue), if a sync weight-raised queue remains empty while in service. Unfortunately, this plugging typically lowers throughput with random I/O, on devices with internal queueing (because it reduces the filling level of the internal queues of the device). This commit addresses this issue by restricting the cases where plugging is performed: if a sync weight-raised queue remains empty while in service, then I/O plugging is performed only if some of the active bfq_queues are *not* weight-raised (which is actually the only circumstance where plugging is needed to preserve the higher share of the throughput of weight-raised queues). This restriction proved able to boost throughput in really many use cases needing only maximum throughput. Signed-off-by: Paolo Valente --- block/bfq-iosched.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c index d94838bcc135..c0b1db3afb81 100644 --- a/block/bfq-iosched.c +++ b/block/bfq-iosched.c @@ -3580,7 +3580,12 @@ static bool bfq_better_to_idle(struct bfq_queue *bfqq) * whether bfqq is being weight-raised, because * bfq_symmetric_scenario() does not take into account also * weight-raised queues (see comments on - * bfq_weights_tree_add()). + * bfq_weights_tree_add()). In particular, if bfqq is being + * weight-raised, it is important to idle only if there are + * other, non-weight-raised queues that may steal throughput + * to bfqq. Actually, we should be even more precise, and + * differentiate between interactive weight raising and + * soft real-time weight raising. * * As a side note, it is worth considering that the above * device-idling countermeasures may however fail in the @@ -3592,7 +3597,8 @@ static bool bfq_better_to_idle(struct bfq_queue *bfqq) * to let requests be served in the desired order until all * the requests already queued in the device have been served. */ - asymmetric_scenario = bfqq->wr_coeff > 1 || + asymmetric_scenario = (bfqq->wr_coeff > 1 && + bfqd->wr_busy_queues < bfqd->busy_queues) || !bfq_symmetric_scenario(bfqd); /*