linux-kernel - Re: [PATCH v1] scsi: ufs-mediatek: Enable UFSHCI_QUIRK_SKIP_MANUAL_WB_FLUSH

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Date:   Mon, 28 Dec 2020 09:33:44 +0800
From:   Can Guo <cang@...eaurora.org>
To:     Stanley Chu <stanley.chu@...iatek.com>
Cc:     Bean Huo <huobean@...il.com>, Avri Altman <Avri.Altman@....com>,
        linux-scsi@...r.kernel.org, martin.petersen@...cle.com,
        alim.akhtar@...sung.com, jejb@...ux.ibm.com, beanhuo@...ron.com,
        asutoshd@...eaurora.org, matthias.bgg@...il.com,
        bvanassche@....org, linux-mediatek@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kuohong.wang@...iatek.com, peter.wang@...iatek.com,
        chun-hung.wu@...iatek.com, andy.teng@...iatek.com,
        chaotian.jing@...iatek.com, cc.chou@...iatek.com,
        jiajie.hao@...iatek.com, alice.chao@...iatek.com
Subject: Re: [PATCH v1] scsi: ufs-mediatek: Enable
 UFSHCI_QUIRK_SKIP_MANUAL_WB_FLUSH_CTRL

On 2020-12-24 21:47, Stanley Chu wrote:
> Hi Avri, Bean,
> 
> On Thu, 2020-12-24 at 13:01 +0100, Bean Huo wrote:
>> On Thu, 2020-12-24 at 11:03 +0000, Avri Altman wrote:
>> > > > Do you see any substantial benefit of having
>> > > > fWriteBoosterBufferFlushEn
>> > > > disabled?
>> > >
>> > > 1. The definition of fWriteBoosterBufferFlushEn is that host allows
>> > > device to do flush in anytime after fWriteBoosterBufferFlushEn is
>> > > set as
>> > > on. This is not what we want.
>> > >
>> > > Just Like BKOP, We do not want flush happening beyond host's
>> > > expected
>> > > timing that device performance may be "randomly" dropped.
>> >
>> > Explicit flush takes place only when the device is idle:
>> > if fWriteBoosterBufferFlushEn is set, the device is idle, and before
>> > h8 received.
>> > If a request arrives, the flush operation should be halted.
>> > So no performance degradation is expected.
>> 
>> Hi Stanley
>> 
>> Avri's comment is correct, fWriteBoosterBufferFlushEn==1, device will
>> flush only when it is in idle, once there is new incoming request, the
>> flush will be suspended. You should be very careful when you want to
>> skip this stetting of this flag.
> 
> Very appreciate your the clarification.
> 
> However similar to "Background Operations Termination Latency", while
> the next request comes, device may need some time to suspend on-going
> flush operations. This delay may "randomly" degrade the performance
> right?

That can be case by case (or vendor by vendor), but generally I agree
with you on this.

> 
> Since the configuration, i.e., enable
> fWriteBoosterBufferFlushDuringHibernate only with
> fWriteBoosterBufferFlushEn disabled, has been applied in many of our
> mass-produced products these yeas, we would like to keep it unless the
> new setting has obvious benefits.

Thanks for sharing the info. I will leave the decision to Asutosh on 
this.

Thanks,
Can Guo.

> 
> Thanks,
> Stanley Chu
> 
>> 
>> Bean
>>