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From: Alan Stern <stern@rowland.harvard.edu>
To: Bart Van Assche <bvanassche@acm.org>
Cc: Martin Kepplinger <martin.kepplinger@puri.sm>,
	jejb@linux.ibm.com, Can Guo <cang@codeaurora.org>,
	martin.petersen@oracle.com, linux-scsi@vger.kernel.org,
	linux-kernel@vger.kernel.org, kernel@puri.sm
Subject: Re: [PATCH] scsi: sd: add runtime pm to open / release
Date: Tue, 30 Jun 2020 15:38:02 -0400
Message-ID: <20200630193802.GA463609@rowland.harvard.edu> (raw)
In-Reply-To: <1804723c-4aaf-a820-d3ef-e70125017cad@acm.org>

On Tue, Jun 30, 2020 at 12:23:12PM -0700, Bart Van Assche wrote:
> On 2020-06-30 11:02, Alan Stern wrote:
> > Right now there doesn't seem to be any mechanism for resuming the queue 
> > if an REQ_PREEMPT request is added while the queue is suspended.
> 
> I do not agree with the above statement. My understanding is that resuming
> happens as follows if a request is submitted against a runtime suspended
> queue owned by a SCSI LLD:
> 
> blk_queue_enter()
>   -> blk_pm_request_resume()

Assume that BLK_MQ_REQ_PREEMPT is set in flags.  Then where exactly 
does blk_queue_enter(q, flags) call blk_pm_request_resume(q)?

Nowhere, as far as I can see.

Alan Stern

>     -> pm_request_resume(dev)
>       -> __pm_runtime_resume(dev, RPM_ASYNC)
>         -> rpm_resume(dev, RPM_ASYNC)
>           -> dev->power.request = RPM_REQ_RESUME;
>           -> queue_work(pm_wq, &dev->power.work)
>             -> pm_runtime_work()
>               -> rpm_resume(dev, RPM_NOWAIT)
>                 -> callback = scsi_runtime_resume;
>                 -> rpm_callback(callback, dev);
>                   -> scsi_runtime_resume(dev);
>                     -> sdev_runtime_resume(dev);
>                       -> blk_pre_runtime_resume(sdev->request_queue);
>                         -> q->rpm_status = RPM_RESUMING;
>                       -> sd_resume(dev);
>                         -> sd_start_stop_device(sdkp);
>                           -> sd_pm_ops.runtime_resume == scsi_execute(sdp, START);
>                             -> blk_get_request(..., ..., BLK_MQ_REQ_PREEMPT)
>                               -> blk_mq_alloc_request()
>                                 -> blk_queue_enter()
>                                 -> __blk_mq_alloc_request()
>                             -> blk_execute_rq()
>                             -> blk_put_request()
>                       -> blk_post_runtime_resume(sdev->request_queue);
>                         -> q->rpm_status = RPM_ACTIVE;
>                         -> pm_runtime_mark_last_busy(q->dev);
>                         -> pm_request_autosuspend(q->dev);
> 
> Bart.

  reply index

Thread overview: 56+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-23 11:10 Martin Kepplinger
2020-06-24 13:33 ` Bart Van Assche
2020-06-25  8:16   ` Martin Kepplinger
2020-06-25 14:52     ` Alan Stern
2020-06-26  3:53     ` Bart Van Assche
2020-06-26 15:07     ` Bart Van Assche
2020-06-26 15:44       ` Alan Stern
2020-06-28  2:37         ` Bart Van Assche
2020-06-28 13:10           ` Alan Stern
2020-06-29  9:42         ` Martin Kepplinger
2020-06-29 16:15           ` Alan Stern
2020-06-29 16:56             ` Bart Van Assche
2020-06-29 17:40               ` Alan Stern
2020-06-30  3:33             ` Martin Kepplinger
2020-06-30 13:38               ` Alan Stern
2020-06-30 15:59             ` Bart Van Assche
2020-06-30 18:02               ` Alan Stern
2020-06-30 19:23                 ` Bart Van Assche
2020-06-30 19:38                   ` Alan Stern [this message]
2020-06-30 23:31                     ` Bart Van Assche
2020-07-01  0:49                       ` Alan Stern
2020-07-06 16:41                         ` Alan Stern
2020-07-28  7:02                           ` Martin Kepplinger
2020-07-28 20:02                             ` Alan Stern
2020-07-29 14:12                               ` Martin Kepplinger
2020-07-29 14:32                                 ` Alan Stern
2020-07-29 14:44                                   ` Martin K. Petersen
2020-07-29 14:56                                     ` Alan Stern
2020-07-29 14:46                                   ` James Bottomley
2020-07-29 14:53                                     ` James Bottomley
2020-07-29 15:40                                       ` Martin Kepplinger
2020-07-29 15:44                                         ` James Bottomley
2020-07-29 16:43                                           ` Martin Kepplinger
2020-07-29 18:25                                             ` Alan Stern
2020-07-29 18:29                                               ` James Bottomley
2020-07-30  8:52                                                 ` Martin Kepplinger
2020-07-30  8:54                                                   ` Martin Kepplinger
2020-07-30 15:10                                                   ` Alan Stern
2020-08-04  9:39                                                     ` Martin Kepplinger
2020-08-07  9:51                                                       ` Martin Kepplinger
2020-08-07 14:30                                                         ` Alan Stern
2020-08-08  6:59                                                           ` Martin Kepplinger
2020-08-08 15:05                                                             ` Alan Stern
2020-08-09  9:20                                                               ` Martin Kepplinger
2020-08-09 15:26                                                                 ` Alan Stern
2020-08-10 12:03                                                                   ` Martin Kepplinger
2020-08-10 14:13                                                                     ` Alan Stern
2020-08-11  7:55                                                                       ` Martin Kepplinger
2020-08-11 13:48                                                                         ` Alan Stern
2020-07-29 15:40                                       ` Alan Stern
2020-07-29 15:49                                         ` James Bottomley
2020-07-29 16:17                                           ` Alan Stern
2020-07-29 15:52                                         ` Martin Kepplinger
2020-07-29 18:10                                   ` Douglas Gilbert
2020-07-30  8:05             ` Martin Kepplinger
2020-07-30 15:14               ` Alan Stern

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