Re: [PATCH v1] scsi: ufs-mediatek: Enable UFSHCI_QUIRK_SKIP_MANUAL_WB_FLUSH_CTRL

[Can Guo]

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