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SubjectRe: [PATCH] scsi: sd: add runtime pm to open / release
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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()
-> 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.

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