From patchwork Wed Apr 8 15:03:59 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Doug Anderson X-Patchwork-Id: 11480283 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id AC916112C for ; Wed, 8 Apr 2020 15:12:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8E898208FE for ; Wed, 8 Apr 2020 15:12:34 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=chromium.org header.i=@chromium.org header.b="WeIoaF6V" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729454AbgDHPMd (ORCPT ); Wed, 8 Apr 2020 11:12:33 -0400 Received: from mail-pf1-f195.google.com ([209.85.210.195]:37748 "EHLO mail-pf1-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729287AbgDHPMc (ORCPT ); Wed, 8 Apr 2020 11:12:32 -0400 Received: by mail-pf1-f195.google.com with SMTP id u65so2526592pfb.4 for ; Wed, 08 Apr 2020 08:12:31 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=ykBFVrZ5VqErlxdGxaznASIr1DPALx6cRNBKHC8zE+4=; b=WeIoaF6VGX20BswqY9TqTj+Q4BN5xdWpQNb+lBxDFRLRQmKlLnHtyLEo9szLuaaWmL uXpXqkrjLeFDrSpJb/pE3XsdBUYkCYg2TKiL8z75XbapAgBEJhKQqHfqot+Y6/AjHT6p PqyW+Y65GrBglvA1WkUvjpo7Yk5AoZ2kfXZMs= 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:mime-version:content-transfer-encoding; bh=ykBFVrZ5VqErlxdGxaznASIr1DPALx6cRNBKHC8zE+4=; b=iuQTfY5DU5JFMcujQI9/TB2KnW+9qSPp6YwoFYeyonGYHY6kn3VZJYqRif3ztN0kcf wU4m8okr7KUF/lerUMLYpXqdRL1HYvig/wLXB39150cwhBGY0ArOjv+1MP2t4P+ugF5Y NRAS13Bmzob60PRDfb4Fj/pGx4Lhoh1NRSPu+gkuLftd76pjhGR18CzgDm2mRb6Upjxm sqsw9p4ewMUn7ExMC/Bl1RzVnd1iafx168lsbnBQ8TphqTrPY7lFzfdcvNzsFDv4qLpz GoV9HdpP9ofi0blu81AhIviaIISeKyTuIU9ARoKY74aRND05MLy15LlaGY3CPrDzsYJ6 52yw== X-Gm-Message-State: AGi0Pub5MtCIK+PxxdXstXZR9OFA/7cKNZKOlg0cn8+JORTcf6juQLgD jLlR/yFAxI1xSdBuFgwdMD0szMKxWtZObw== X-Google-Smtp-Source: APiQypKEWc3MCkral5p3jzK3p9lOhhJpdLJZpPnwPUwZmxycNIYMNVYj0LsS1r4g9XYOgoQikNcQMw== X-Received: by 2002:a63:7a07:: with SMTP id v7mr6385580pgc.302.1586358272199; Wed, 08 Apr 2020 08:04:32 -0700 (PDT) Received: from tictac2.mtv.corp.google.com ([2620:15c:202:1:24fa:e766:52c9:e3b2]) by smtp.gmail.com with ESMTPSA id d85sm1468083pfd.157.2020.04.08.08.04.31 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 08 Apr 2020 08:04:31 -0700 (PDT) From: Douglas Anderson To: axboe@kernel.dk, jejb@linux.ibm.com, martin.petersen@oracle.com Cc: paolo.valente@linaro.org, groeck@chromium.org, Gwendal Grignou , linux-scsi@vger.kernel.org, linux-block@vger.kernel.org, Ming Lei , sqazi@google.com, Douglas Anderson , linux-kernel@vger.kernel.org Subject: [PATCH v4 1/4] blk-mq: In blk_mq_dispatch_rq_list() "no budget" is a reason to kick Date: Wed, 8 Apr 2020 08:03:59 -0700 Message-Id: <20200408080255.v4.1.I1f95c459e51962b8d2c83e869913b6befda2255c@changeid> X-Mailer: git-send-email 2.26.0.292.g33ef6b2f38-goog In-Reply-To: <20200408150402.21208-1-dianders@chromium.org> References: <20200408150402.21208-1-dianders@chromium.org> MIME-Version: 1.0 Sender: linux-scsi-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-scsi@vger.kernel.org In blk_mq_dispatch_rq_list(), if blk_mq_sched_needs_restart() returns true and the driver returns BLK_STS_RESOURCE then we'll kick the queue. However, there's another case where we might need to kick it. If we were unable to get budget we can be in much the same state as when the driver returns BLK_STS_RESOURCE, so we should treat it the same. It should be noted that even if we add a whole bunch of extra kicking to the queue in other patches this patch is still important. Specifically any kicking that happened before we re-spliced leftover requests into 'hctx->dispatch' wouldn't have found any work, so we really need to make sure we kick ourselves after we've done the splicing. Signed-off-by: Douglas Anderson Reviewed-by: Ming Lei --- Changes in v4: None Changes in v3: - Note why blk_mq_dispatch_rq_list() change is needed. Changes in v2: None block/blk-mq.c | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-) diff --git a/block/blk-mq.c b/block/blk-mq.c index d92088dec6c3..2cd8d2b49ff4 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -1189,6 +1189,7 @@ bool blk_mq_dispatch_rq_list(struct request_queue *q, struct list_head *list, bool no_tag = false; int errors, queued; blk_status_t ret = BLK_STS_OK; + bool no_budget_avail = false; if (list_empty(list)) return false; @@ -1205,8 +1206,10 @@ bool blk_mq_dispatch_rq_list(struct request_queue *q, struct list_head *list, rq = list_first_entry(list, struct request, queuelist); hctx = rq->mq_hctx; - if (!got_budget && !blk_mq_get_dispatch_budget(hctx)) + if (!got_budget && !blk_mq_get_dispatch_budget(hctx)) { + no_budget_avail = true; break; + } if (!blk_mq_get_driver_tag(rq)) { /* @@ -1311,13 +1314,15 @@ bool blk_mq_dispatch_rq_list(struct request_queue *q, struct list_head *list, * * If driver returns BLK_STS_RESOURCE and SCHED_RESTART * bit is set, run queue after a delay to avoid IO stalls - * that could otherwise occur if the queue is idle. + * that could otherwise occur if the queue is idle. We'll do + * similar if we couldn't get budget and SCHED_RESTART is set. */ needs_restart = blk_mq_sched_needs_restart(hctx); if (!needs_restart || (no_tag && list_empty_careful(&hctx->dispatch_wait.entry))) blk_mq_run_hw_queue(hctx, true); - else if (needs_restart && (ret == BLK_STS_RESOURCE)) + else if (needs_restart && (ret == BLK_STS_RESOURCE || + no_budget_avail)) blk_mq_delay_run_hw_queue(hctx, BLK_MQ_RESOURCE_DELAY); blk_mq_update_dispatch_busy(hctx, true); From patchwork Wed Apr 8 15:04:00 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Doug Anderson X-Patchwork-Id: 11480271 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 339FC112C for ; Wed, 8 Apr 2020 15:04:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 151C520730 for ; Wed, 8 Apr 2020 15:04:37 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=chromium.org header.i=@chromium.org header.b="aL8VsGju" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728533AbgDHPEg (ORCPT ); Wed, 8 Apr 2020 11:04:36 -0400 Received: from mail-pl1-f195.google.com ([209.85.214.195]:34097 "EHLO mail-pl1-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727800AbgDHPEg (ORCPT ); Wed, 8 Apr 2020 11:04:36 -0400 Received: by mail-pl1-f195.google.com with SMTP id a23so2608663plm.1 for ; Wed, 08 Apr 2020 08:04:34 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=99bGb9kPLJIKPGAYnWeUQM+upQBOmhTKAuXfLDA02as=; b=aL8VsGjuULtKfOLQ4xJAOYPOZmY0Fm4LmPDtmN2EaK+l6PCc9odZkH+cahGM56TX7V RRRVicea4VeZOdbhSkDKFRCH58KpGUJ7CNOXzRWeuJNXr7aH2Mg1BkRpLSkVcDhAuWap 3QS1w5M7oxl5CLQ+/jYNLGia4XietUIz9CYHU= 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:mime-version:content-transfer-encoding; bh=99bGb9kPLJIKPGAYnWeUQM+upQBOmhTKAuXfLDA02as=; b=MwgQxqBq7deci+MpWpQQS0oiIqPnH4+mmzMWkMcLBi1c4esQ70U4NpiGUyhAwLjou7 tWcJod/nxDWeCmYcNzbs/lwfgubi8hnbVnWi4UZpWb4hg/0TZsO46Gq+YXgau5ywNkWP hoZ0olBnENoqUbvl34FMN3v6ZEOGu9/xFUarvvTsm3O2j8jqcMzyLgXIpu2cF5n7RANU FmnV9c3KJnXEJxz8Br1zNqVwaiwBvPJ/CKNjWS3AtqZ/BXBs8JHBFKpgdCZ//qgQMjJ1 HiB707Z7hDI3w8jTwyD5iKVXW48MXOyQdL8KNgkfP/UKTMQXil+kUkfiz/N0nMgH8zqk foyA== X-Gm-Message-State: AGi0PubIadf6jHcEujrjkKfzfioxaUyb3nSmKBedBHmnJieni3ZCEkpF DIJIpZtcjxrMCZwLh0pLaaUeJA== X-Google-Smtp-Source: APiQypLwTROlMgk5kYCTxCFF56//DDLXDI3u7/I38vnrWOWWHtwiZKkjylcUiWynghi29M6bg7W1mQ== X-Received: by 2002:a17:90a:178e:: with SMTP id q14mr208304pja.132.1586358273435; Wed, 08 Apr 2020 08:04:33 -0700 (PDT) Received: from tictac2.mtv.corp.google.com ([2620:15c:202:1:24fa:e766:52c9:e3b2]) by smtp.gmail.com with ESMTPSA id d85sm1468083pfd.157.2020.04.08.08.04.32 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 08 Apr 2020 08:04:32 -0700 (PDT) From: Douglas Anderson To: axboe@kernel.dk, jejb@linux.ibm.com, martin.petersen@oracle.com Cc: paolo.valente@linaro.org, groeck@chromium.org, Gwendal Grignou , linux-scsi@vger.kernel.org, linux-block@vger.kernel.org, Ming Lei , sqazi@google.com, Douglas Anderson , =?utf-8?q?Andr?= =?utf-8?q?=C3=A9_Almeida?= , Bart Van Assche , Damien Le Moal , John Garry , Pavel Begunkov , Sagi Grimberg , linux-kernel@vger.kernel.org Subject: [PATCH v4 2/4] blk-mq: Add blk_mq_delay_run_hw_queues() API call Date: Wed, 8 Apr 2020 08:04:00 -0700 Message-Id: <20200408080255.v4.2.I4c665d70212a5b33e103fec4d5019a59b4c05577@changeid> X-Mailer: git-send-email 2.26.0.292.g33ef6b2f38-goog In-Reply-To: <20200408150402.21208-1-dianders@chromium.org> References: <20200408150402.21208-1-dianders@chromium.org> MIME-Version: 1.0 Sender: linux-scsi-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-scsi@vger.kernel.org We have: * blk_mq_run_hw_queue() * blk_mq_delay_run_hw_queue() * blk_mq_run_hw_queues() ...but not blk_mq_delay_run_hw_queues(), presumably because nobody needed it before now. Since we need it for a later patch in this series, add it. Signed-off-by: Douglas Anderson Reviewed-by: Ming Lei --- Changes in v4: None Changes in v3: - ("blk-mq: Add blk_mq_delay_run_hw_queues() API call") new for v3 Changes in v2: None block/blk-mq.c | 19 +++++++++++++++++++ include/linux/blk-mq.h | 1 + 2 files changed, 20 insertions(+) diff --git a/block/blk-mq.c b/block/blk-mq.c index 2cd8d2b49ff4..ea0cd970a3ff 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -1537,6 +1537,25 @@ void blk_mq_run_hw_queues(struct request_queue *q, bool async) } EXPORT_SYMBOL(blk_mq_run_hw_queues); +/** + * blk_mq_delay_run_hw_queues - Run all hardware queues asynchronously. + * @q: Pointer to the request queue to run. + * @msecs: Microseconds of delay to wait before running the queues. + */ +void blk_mq_delay_run_hw_queues(struct request_queue *q, unsigned long msecs) +{ + struct blk_mq_hw_ctx *hctx; + int i; + + queue_for_each_hw_ctx(q, hctx, i) { + if (blk_mq_hctx_stopped(hctx)) + continue; + + blk_mq_delay_run_hw_queue(hctx, msecs); + } +} +EXPORT_SYMBOL(blk_mq_delay_run_hw_queues); + /** * blk_mq_queue_stopped() - check whether one or more hctxs have been stopped * @q: request queue. diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h index 11cfd6470b1a..405f8c196517 100644 --- a/include/linux/blk-mq.h +++ b/include/linux/blk-mq.h @@ -503,6 +503,7 @@ void blk_mq_unquiesce_queue(struct request_queue *q); void blk_mq_delay_run_hw_queue(struct blk_mq_hw_ctx *hctx, unsigned long msecs); void blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx, bool async); void blk_mq_run_hw_queues(struct request_queue *q, bool async); +void blk_mq_delay_run_hw_queues(struct request_queue *q, unsigned long msecs); void blk_mq_tagset_busy_iter(struct blk_mq_tag_set *tagset, busy_tag_iter_fn *fn, void *priv); void blk_mq_tagset_wait_completed_request(struct blk_mq_tag_set *tagset); From patchwork Wed Apr 8 15:04:01 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Doug Anderson X-Patchwork-Id: 11480273 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id B55F414B4 for ; Wed, 8 Apr 2020 15:04:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8E7DA20730 for ; Wed, 8 Apr 2020 15:04:38 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=chromium.org header.i=@chromium.org header.b="NrKiFeVe" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728691AbgDHPEi (ORCPT ); Wed, 8 Apr 2020 11:04:38 -0400 Received: from mail-pg1-f193.google.com ([209.85.215.193]:39452 "EHLO mail-pg1-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727800AbgDHPEi (ORCPT ); Wed, 8 Apr 2020 11:04:38 -0400 Received: by mail-pg1-f193.google.com with SMTP id g32so3430409pgb.6 for ; Wed, 08 Apr 2020 08:04:36 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=rDHN9ShJvPz0UC+OvvEBSbpZQdwfsROoxRdOsJpjLv0=; 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Wed, 08 Apr 2020 08:04:35 -0700 (PDT) Received: from tictac2.mtv.corp.google.com ([2620:15c:202:1:24fa:e766:52c9:e3b2]) by smtp.gmail.com with ESMTPSA id d85sm1468083pfd.157.2020.04.08.08.04.33 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 08 Apr 2020 08:04:34 -0700 (PDT) From: Douglas Anderson To: axboe@kernel.dk, jejb@linux.ibm.com, martin.petersen@oracle.com Cc: paolo.valente@linaro.org, groeck@chromium.org, Gwendal Grignou , linux-scsi@vger.kernel.org, linux-block@vger.kernel.org, Ming Lei , sqazi@google.com, Douglas Anderson , linux-kernel@vger.kernel.org Subject: [PATCH v4 3/4] blk-mq: Rerun dispatching in the case of budget contention Date: Wed, 8 Apr 2020 08:04:01 -0700 Message-Id: <20200408080255.v4.3.I28278ef8ea27afc0ec7e597752a6d4e58c16176f@changeid> X-Mailer: git-send-email 2.26.0.292.g33ef6b2f38-goog In-Reply-To: <20200408150402.21208-1-dianders@chromium.org> References: <20200408150402.21208-1-dianders@chromium.org> MIME-Version: 1.0 Sender: linux-scsi-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-scsi@vger.kernel.org If ever a thread running blk-mq code tries to get budget and fails it immediately stops doing work and assumes that whenever budget is freed up that queues will be kicked and whatever work the thread was trying to do will be tried again. One path where budget is freed and queues are kicked in the normal case can be seen in scsi_finish_command(). Specifically: - scsi_finish_command() - scsi_device_unbusy() - # Decrement "device_busy", AKA release budget - scsi_io_completion() - scsi_end_request() - blk_mq_run_hw_queues() The above is all well and good. The problem comes up when a thread claims the budget but then releases it without actually dispatching any work. Since we didn't schedule any work we'll never run the path of finishing work / kicking the queues. This isn't often actually a problem which is why this issue has existed for a while and nobody noticed. Specifically we only get into this situation when we unexpectedly found that we weren't going to do any work. Code that later receives new work kicks the queues. All good, right? The problem shows up, however, if timing is just wrong and we hit a race. To see this race let's think about the case where we only have a budget of 1 (only one thread can hold budget). Now imagine that a thread got budget and then decided not to dispatch work. It's about to call put_budget() but then the thread gets context switched out for a long, long time. While in this state, any and all kicks of the queue (like the when we received new work) will be no-ops because nobody can get budget. Finally the thread holding budget gets to run again and returns. All the normal kicks will have been no-ops and we have an I/O stall. As you can see from the above, you need just the right timing to see the race. To start with, the only case it happens if we thought we had work, actually managed to get the budget, but then actually didn't have work. That's pretty rare to start with. Even then, there's usually a very small amount of time between realizing that there's no work and putting the budget. During this small amount of time new work has to come in and the queue kick has to make it all the way to trying to get the budget and fail. It's pretty unlikely. One case where this could have failed is illustrated by an example of threads running blk_mq_do_dispatch_sched(): * Threads A and B both run has_work() at the same time with the same "hctx". Imagine has_work() is exact. There's no lock, so it's OK if Thread A and B both get back true. * Thread B gets interrupted for a long time right after it decides that there is work. Maybe its CPU gets an interrupt and the interrupt handler is slow. * Thread A runs, get budget, dispatches work. * Thread A's work finishes and budget is released. * Thread B finally runs again and gets budget. * Since Thread A already took care of the work and no new work has come in, Thread B will get NULL from dispatch_request(). I believe this is specifically why dispatch_request() is allowed to return NULL in the first place if has_work() must be exact. * Thread B will now be holding the budget and is about to call put_budget(), but hasn't called it yet. * Thread B gets interrupted for a long time (again). Dang interrupts. * Now Thread C (maybe with a different "hctx" but the same queue) comes along and runs blk_mq_do_dispatch_sched(). * Thread C won't do anything because it can't get budget. * Finally Thread B will run again and put the budget without kicking any queues. Even though the example above is with blk_mq_do_dispatch_sched() I believe the race is possible any time someone is holding budget but doesn't do work. Unfortunately, the unlikely has become more likely if you happen to be using the BFQ I/O scheduler. BFQ, by design, sometimes returns "true" for has_work() but then NULL for dispatch_request() and stays in this state for a while (currently up to 9 ms). Suddenly you only need one race to hit, not two races in a row. With my current setup this is easy to reproduce in reboot tests and traces have actually shown that we hit a race similar to the one described above. Note that we only need to fix blk_mq_do_dispatch_sched() and blk_mq_do_dispatch_ctx() and not the other places that put budget. In other cases we know that we have work to do on at least one "hctx" and code already exists to kick that "hctx"'s queue. When that work finally finishes all the queues will be kicked using the normal flow. One last note is that (at least in the SCSI case) budget is shared by all "hctx"s that have the same queue. Thus we need to make sure to kick the whole queue, not just re-run dispatching on a single "hctx". Signed-off-by: Douglas Anderson Reviewed-by: Ming Lei --- Changes in v4: - Only kick in blk_mq_do_dispatch_ctx() / blk_mq_do_dispatch_sched(). Changes in v3: - Always kick when putting the budget. - Delay blk_mq_do_dispatch_sched() kick by 3 ms for inexact has_work(). - Totally rewrote commit message. Changes in v2: - Replace ("scsi: core: Fix stall...") w/ ("blk-mq: Rerun dispatch...") block/blk-mq-sched.c | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c index 74cedea56034..eca81bd4010c 100644 --- a/block/blk-mq-sched.c +++ b/block/blk-mq-sched.c @@ -80,6 +80,8 @@ void blk_mq_sched_restart(struct blk_mq_hw_ctx *hctx) blk_mq_run_hw_queue(hctx, true); } +#define BLK_MQ_BUDGET_DELAY 3 /* ms units */ + /* * Only SCSI implements .get_budget and .put_budget, and SCSI restarts * its queue by itself in its completion handler, so we don't need to @@ -103,6 +105,14 @@ static void blk_mq_do_dispatch_sched(struct blk_mq_hw_ctx *hctx) rq = e->type->ops.dispatch_request(hctx); if (!rq) { blk_mq_put_dispatch_budget(hctx); + /* + * We're releasing without dispatching. Holding the + * budget could have blocked any "hctx"s with the + * same queue and if we didn't dispatch then there's + * no guarantee anyone will kick the queue. Kick it + * ourselves. + */ + blk_mq_delay_run_hw_queues(q, BLK_MQ_BUDGET_DELAY); break; } @@ -149,6 +159,14 @@ static void blk_mq_do_dispatch_ctx(struct blk_mq_hw_ctx *hctx) rq = blk_mq_dequeue_from_ctx(hctx, ctx); if (!rq) { blk_mq_put_dispatch_budget(hctx); + /* + * We're releasing without dispatching. Holding the + * budget could have blocked any "hctx"s with the + * same queue and if we didn't dispatch then there's + * no guarantee anyone will kick the queue. Kick it + * ourselves. + */ + blk_mq_delay_run_hw_queues(q, BLK_MQ_BUDGET_DELAY); break; } From patchwork Wed Apr 8 15:04:02 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Doug Anderson X-Patchwork-Id: 11480275 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 4CAE014B4 for ; Wed, 8 Apr 2020 15:04:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2D78220730 for ; Wed, 8 Apr 2020 15:04:42 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=chromium.org header.i=@chromium.org header.b="RVJkQ7hr" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729287AbgDHPEl (ORCPT ); Wed, 8 Apr 2020 11:04:41 -0400 Received: from mail-pf1-f194.google.com ([209.85.210.194]:33255 "EHLO mail-pf1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728620AbgDHPEk (ORCPT ); Wed, 8 Apr 2020 11:04:40 -0400 Received: by mail-pf1-f194.google.com with SMTP id c138so3174073pfc.0 for ; Wed, 08 Apr 2020 08:04:39 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=V7jm6LpOOba6AShtQDS9c6sItWuCS66vjofoe5YuiE4=; b=RVJkQ7hrtx/hJqp9SyS8a/6H90Yi26GUw3MAk2MsBz2Po5NpDAosNRaETNYCYW5o0w ykePsQQP91ugsXr2roLsaXUNJ0W2CuDK3R8H+PuKPcxuI0oVH3csLak7G3gnyrb24oIE BAaIhmv6eZuom8joh7i06yEvMXG2iAlXlcDbo= 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:mime-version:content-transfer-encoding; bh=V7jm6LpOOba6AShtQDS9c6sItWuCS66vjofoe5YuiE4=; b=Jv3g5z2K65TqxR9/IkZu+ZcCGKgHtj3u2nN9/wGPzmh8o6u4jY8fe/9OsN1J0sQ9qH 3uKBg5bEHJ3uB5BZqsvGkKXwps+I4Y3qSVF/kleixImg8jvv3jZLRbRMH8jwZiw4eA3r aSfRud9HA43xQe0aj4hx0R4+suXUi/pNfFDTweDYAIL+pOqvp5fwhMzVqzKUFggJpCza xqGIArld3ZNG/hi4xuzOGH4m5PUTivHGNYC6XxkjGVNHpjcconXHG+uq+ZBH3bda2N2l iEJ/mPyDmqQjdUeay+qdpYK0R2U1FVbPPsWgPc/aLr2CCfqFUMlOuPSejREhHvpD2dlY Cgow== X-Gm-Message-State: AGi0PuZqfhMM21WtAZq9CDmrWAq75fUh2Yqn49Ara1xmzGPYnco05jBp M3R3apeXGYWvrwDyARxd75zaKg== X-Google-Smtp-Source: APiQypIz1G9cPCJpf4iXpx7RsV38wvJ0SkqcWHSSgCLSAaQfpBIOel67MdUS8T7gg/yBEMN2Opta/w== X-Received: by 2002:a63:e10f:: with SMTP id z15mr7474924pgh.88.1586358277236; Wed, 08 Apr 2020 08:04:37 -0700 (PDT) Received: from tictac2.mtv.corp.google.com ([2620:15c:202:1:24fa:e766:52c9:e3b2]) by smtp.gmail.com with ESMTPSA id d85sm1468083pfd.157.2020.04.08.08.04.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 08 Apr 2020 08:04:36 -0700 (PDT) From: Douglas Anderson To: axboe@kernel.dk, jejb@linux.ibm.com, martin.petersen@oracle.com Cc: paolo.valente@linaro.org, groeck@chromium.org, Gwendal Grignou , linux-scsi@vger.kernel.org, linux-block@vger.kernel.org, Ming Lei , sqazi@google.com, Douglas Anderson , linux-kernel@vger.kernel.org Subject: [PATCH v4 4/4] Revert "scsi: core: run queue if SCSI device queue isn't ready and queue is idle" Date: Wed, 8 Apr 2020 08:04:02 -0700 Message-Id: <20200408080255.v4.4.I630e6ca4cdcf9ab13ea899274745f9e3174eb12b@changeid> X-Mailer: git-send-email 2.26.0.292.g33ef6b2f38-goog In-Reply-To: <20200408150402.21208-1-dianders@chromium.org> References: <20200408150402.21208-1-dianders@chromium.org> MIME-Version: 1.0 Sender: linux-scsi-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-scsi@vger.kernel.org This reverts commit 7e70aa789d4a0c89dbfbd2c8a974a4df717475ec. Now that we have the patches ("blk-mq: In blk_mq_dispatch_rq_list() "no budget" is a reason to kick") and ("blk-mq: Rerun dispatching in the case of budget contention") we should no longer need the fix in the SCSI code. Revert it, resolving conflicts with other patches that have touched this code. With this revert (and the two new patches) I can run the script that was in commit 7e70aa789d4a ("scsi: core: run queue if SCSI device queue isn't ready and queue is idle") in a loop with no failure. If I do this revert without the two new patches I can easily get a failure. Signed-off-by: Douglas Anderson Reviewed-by: Ming Lei Acked-by: Martin K. Petersen --- I don't know for sure that we can revert this patch, but in the very least the original test case now passes. If there is any question about this, we can just drop this patch. Changes in v4: None Changes in v3: - ("Revert "scsi: core: run queue...") new for v3. Changes in v2: None drivers/scsi/scsi_lib.c | 7 +------ 1 file changed, 1 insertion(+), 6 deletions(-) diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c index 610ee41fa54c..b9e28ea76cc0 100644 --- a/drivers/scsi/scsi_lib.c +++ b/drivers/scsi/scsi_lib.c @@ -1632,12 +1632,7 @@ static bool scsi_mq_get_budget(struct blk_mq_hw_ctx *hctx) struct request_queue *q = hctx->queue; struct scsi_device *sdev = q->queuedata; - if (scsi_dev_queue_ready(q, sdev)) - return true; - - if (atomic_read(&sdev->device_busy) == 0 && !scsi_device_blocked(sdev)) - blk_mq_delay_run_hw_queue(hctx, SCSI_QUEUE_DELAY); - return false; + return scsi_dev_queue_ready(q, sdev); } static blk_status_t scsi_queue_rq(struct blk_mq_hw_ctx *hctx,