linux-kernel - RE:(2) [PATCH] scsi: ufs: Optimize the WB flush process to save device power consumption

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Date:   Thu, 29 Jun 2023 12:11:52 +0900
From:   Jinyoung CHOI <j-young.choi@...sung.com>
To:     Avri Altman <Avri.Altman@....com>, Lu Hongfei <luhongfei@...o.com>,
        ALIM AKHTAR <alim.akhtar@...sung.com>,
        Bart Van Assche <bvanassche@....org>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Stanley Chu <stanley.chu@...iatek.com>,
        Bean Huo <beanhuo@...ron.com>,
        Asutosh Das <quic_asutoshd@...cinc.com>,
        "Bao D. Nguyen" <quic_nguyenb@...cinc.com>,
        Keoseong Park <keosung.park@...sung.com>,
        Arthur Simchaev <Arthur.Simchaev@....com>,
        "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     "opensource.kernel@...o.com" <opensource.kernel@...o.com>,
        Tang Huan <tanghuan@...o.com>
Subject: RE:(2) [PATCH] scsi: ufs: Optimize the WB flush process to save
 device power consumption

>> 
>> In the original logic, WB Hibern Flush was always on.
>> During suspend flow, the host will determine whether the device needs
>> BKOP or WB flush, and if so, it will keep VCC supply.
>> WB flush is only a part of BKOP, and device that needs BKOP do not
>> necessarily need WB flush if the conditions are not met. Therefore,
>> if WB flush is not needed, it will be better to disable WB Hibern
>> Flush,..... 
>I beg to differ on this conclusion.
>If you expect SLC write performance, without fluctuations,
>the host should let the device manage its wb buffer on its own.
>This is exactly what flush on hibernate does and better leave it be.
>
>Thanks,
>Avri

Hi, Lu Hongfei.

I agree with avri.
In fact, I am not sure if there will be a significant improvement in
power consumption.
In addition, for the toggle of the function, a code that compares with
the existing value must be added to prevent unnecessary queries.

Best Regards,
Jinyoung.