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

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Date:   Thu, 24 Dec 2020 21:47:37 +0800
From:   Stanley Chu <stanley.chu@...iatek.com>
To:     Bean Huo <huobean@...il.com>
CC:     Avri Altman <Avri.Altman@....com>, Can Guo <cang@...eaurora.org>,
        "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        "martin.petersen@...cle.com" <martin.petersen@...cle.com>,
        "alim.akhtar@...sung.com" <alim.akhtar@...sung.com>,
        "jejb@...ux.ibm.com" <jejb@...ux.ibm.com>,
        "beanhuo@...ron.com" <beanhuo@...ron.com>,
        "asutoshd@...eaurora.org" <asutoshd@...eaurora.org>,
        "matthias.bgg@...il.com" <matthias.bgg@...il.com>,
        "bvanassche@....org" <bvanassche@....org>,
        "linux-mediatek@...ts.infradead.org" 
        <linux-mediatek@...ts.infradead.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kuohong.wang@...iatek.com" <kuohong.wang@...iatek.com>,
        "peter.wang@...iatek.com" <peter.wang@...iatek.com>,
        "chun-hung.wu@...iatek.com" <chun-hung.wu@...iatek.com>,
        "andy.teng@...iatek.com" <andy.teng@...iatek.com>,
        "chaotian.jing@...iatek.com" <chaotian.jing@...iatek.com>,
        "cc.chou@...iatek.com" <cc.chou@...iatek.com>,
        "jiajie.hao@...iatek.com" <jiajie.hao@...iatek.com>,
        "alice.chao@...iatek.com" <alice.chao@...iatek.com>
Subject: Re: [PATCH v1] scsi: ufs-mediatek: Enable
 UFSHCI_QUIRK_SKIP_MANUAL_WB_FLUSH_CTRL

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?

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,
Stanley Chu

> 
> Bean
>