Message-ID: <c92bec14-8457-7992-6714-398b467b67e3@intel.com>
Date:   Tue, 23 Mar 2021 21:19:25 +0200
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     "Asutosh Das (asd)" <asutoshd@...eaurora.org>, cang@...eaurora.org,
        martin.petersen@...cle.com, linux-scsi@...r.kernel.org
Cc:     linux-arm-msm@...r.kernel.org,
        Alim Akhtar <alim.akhtar@...sung.com>,
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        Stanley Chu <stanley.chu@...iatek.com>,
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Subject: Re: [PATCH v12 1/2] scsi: ufs: Enable power management for wlun

On 23/03/21 5:13 pm, Asutosh Das (asd) wrote:
> On 3/22/2021 11:12 PM, Adrian Hunter wrote:
>> On 22/03/21 9:53 pm, Asutosh Das (asd) wrote:
>>> On 3/19/2021 10:47 AM, Adrian Hunter wrote:
>>>> On 19/03/21 2:35 am, Asutosh Das wrote:
>>>>> During runtime-suspend of ufs host, the scsi devices are
>>>>> already suspended and so are the queues associated with them.
>>>>> But the ufs host sends SSU to wlun during its runtime-suspend.
>>>>> During the process blk_queue_enter checks if the queue is not in
>>>>> suspended state. If so, it waits for the queue to resume, and never
>>>>> comes out of it.
>>>>> The commit
>>>>> (d55d15a33: scsi: block: Do not accept any requests while suspended)
>>>>> adds the check if the queue is in suspended state in blk_queue_enter().
>>>>>
>>>>> Call trace:
>>>>>    __switch_to+0x174/0x2c4
>>>>>    __schedule+0x478/0x764
>>>>>    schedule+0x9c/0xe0
>>>>>    blk_queue_enter+0x158/0x228
>>>>>    blk_mq_alloc_request+0x40/0xa4
>>>>>    blk_get_request+0x2c/0x70
>>>>>    __scsi_execute+0x60/0x1c4
>>>>>    ufshcd_set_dev_pwr_mode+0x124/0x1e4
>>>>>    ufshcd_suspend+0x208/0x83c
>>>>>    ufshcd_runtime_suspend+0x40/0x154
>>>>>    ufshcd_pltfrm_runtime_suspend+0x14/0x20
>>>>>    pm_generic_runtime_suspend+0x28/0x3c
>>>>>    __rpm_callback+0x80/0x2a4
>>>>>    rpm_suspend+0x308/0x614
>>>>>    rpm_idle+0x158/0x228
>>>>>    pm_runtime_work+0x84/0xac
>>>>>    process_one_work+0x1f0/0x470
>>>>>    worker_thread+0x26c/0x4c8
>>>>>    kthread+0x13c/0x320
>>>>>    ret_from_fork+0x10/0x18
>>>>>
>>>>> Fix this by registering ufs device wlun as a scsi driver and
>>>>> registering it for block runtime-pm. Also make this as a
>>>>> supplier for all other luns. That way, this device wlun
>>>>> suspends after all the consumers and resumes after
>>>>> hba resumes.
>>>>>
>>>>> Co-developed-by: Can Guo <cang@...eaurora.org>
>>>>> Signed-off-by: Can Guo <cang@...eaurora.org>
>>>>> Signed-off-by: Asutosh Das <asutoshd@...eaurora.org>
>>>>
>>>> I have some more comments that may help straighten things out.
>>>>
>>>> Also please look at ufs_debugfs_get_user_access() and
>>>> ufs_debugfs_put_user_access() that now need to scsi_autopm_get/put_device
>>>> sdev_ufs_device.
>>>>
>>>> It would also be good if you could re-base on linux-next.
>>>>
>>>
>>> Hi Adrian
>>> Thanks for the comments.
>>>
>>> I agree moving the code to wlun probe and other changes.
>>> But it looks to me that it may not fully solve the issue.
>>>
>>> Please let me explain my understanding on this:
>>>
>>> (Please refer to the logs in v10)
>>> scsi_autopm_*() are invoked on a sdev.
>>> pm_runtime_get_suppliers()/rpm_put_suppliers() are on the supplier device.
>>>
>>> For the device wlun:
>>>      slave_configure():
>>>          - doesn't set the rpm_autosuspend
>>>          - pm_runtime_getnoresume()
>>>      scsi_sysfs_add_sdev():
>>>          - pm_runtime_forbid()
>>>          - scsi_autopm_get_device()
>>>          - device_add()
>>>              - ufshcd_wl_probe()
>>>          - scsi_autopm_put_device()
>>>
>>> For all other scsi devices:
>>>      slave_alloc():
>>>          - ufshcd_setup_links()
>>> Say all link_add: pm_runtime_put(&hba->sdev_ufs_device->sdev_gendev);
>>
>> With DL_FLAG_RPM_ACTIVE, links will 'get' not 'put'
>>
> I'm referring to the pm_runtime_put(sdev_ufs_device) after all the links are setup, that you suggested to add.

Ok

>>>      slave_configure():
>>>          - set rpm_autosuspend
>>>      scsi_sysfs_add_sdev():
>>>          - scsi_autopm_get_device()
>>>          - device_add() -> schedules an async probe()
>>>          - scsi_autopm_put_device() - (1)
>>>
>>> Now the rpm_put_suppliers() can be invoked *after* pm_runtime_get_suppliers() of the async probe(), since both are running in different contexts.
>>
>> Only if the sd device suspends.
>>
> Correct. What'd stop the sd device from suspending?
> We should be stopping the sd device from suspending here - imho.

You mean for performance reasons.  That is something we can
look at, but let's get it working first.

> 
>>> In that case, the usage_count of supplier would be decremented until rpm_active of this link becomes 1.
>>
>> Right, because the sd device suspended.
>>
>>> Now the pm_runtime_get_suppliers() expects the link_active to be more than 1.
>>
>> Not sure what you mean here. pm_runtime_*put*_suppliers() won't do anything if the link count is 1.
> I'm referring to the logs that I pasted before:
> [    6.941267][    T7] scsi 0:0:0:4: rpm_put_suppliers: [BEF] Supp (0:0:0:49488) usage_count: 4 rpm_active: 3
> 
> ------ T196 Context comes in while T7 is running ----------
> [    6.941466][  T196] scsi 0:0:0:4: pm_runtime_get_suppliers: (0:0:0:49488): supp: usage_count: 5 rpm_active: 4
> --------------------------------------------------------------
> 
> [    7.788397][    T7] scsi 0:0:0:4: rpm_put_suppliers: [AFT] Supp (0:0:0:49488) usage_count: 2 rpm_active: 1
> 
> I meant to say that, if the rpm_put_suppliers() is invoked after the pm_runtime_get_suppliers() as is seen above then the link_active may become 1 even *after* pm_runtime_get_suppliers() is invoked.
> 
> I'm referring to the pm_runtime_get_suppliers() invoked from:
> driver_probe_device() - say for, sd 0:0:0:x
>     |- pm_runtime_get_suppliers() - for sd 0:0:0:49488

I am hoping that was the problem that Rafael's revert dealt with.

>>
>>> Now then, there comes a time, that when sd_probe() schedules a suspend, the supplier usage_count becomes 0 and the link_active becomes 1.
>>> And the supplier suspends before the consumer.
>>
>> sd probe first resumes the sd device which will resume the supplier.
>>
> Correct, but it'd again schedule a suspend (since autosuspend is enabled now) at the end of the sd_probe().
> Thereafter, pm_runtime_put_suppliers()(sd 0:0:0:49488) is invoked from driver_probe_device() which had actually invoked sd_probe().
> That'd make the link_active to 1 even when sd 0:0:0:x is active.

If sd 0:0:0:x is active then rpm_get_suppliers() still has +1 rpm_active. pm_runtime_get_suppliers() also has +1 rpm_active.
i.e. rpm_active is 3. If rpm_put_suppliers() is called, it means sd 0:0:0:x has really runtime suspended (not just waiting for autosuspend.  Otherwise when the probe ends pm_runtime_put_suppliers() will drop rpm_active from 3 to 2.

But it is a bit theoretical.  Let's try it and see.

> 
>>>
>>> So I was wondering, what'd make sure that the pm_runtime_get_suppliers() from driver_probe_device() is invoked after scsi_autopm_put_device() (1) finishes the rpm_put_suppliers().
>>>
>>> Am not sure if I'm missing something in this.
>>> Do you think, the current changes alone can fix the above issue?
>>
>> Yes, but let's see.
>>
> Essentially, we should stop the sd device from runtime suspending until it's probe is done. Then allow the same. Does it make sense?
> Please let me know what you think.

I really think it would be good to try the changes that have been identified and see how it behaves.

Then go from there.

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