linux-kernel - Re: [RFC PATCH v3 0/5] scsi: ufs: Add Host Performance Booster Support

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Date:   Mon, 29 Jun 2020 13:39:42 +0200
From:   Bean Huo <huobean@...il.com>
To:     Avri Altman <Avri.Altman@....com>,
        "daejun7.park@...sung.com" <daejun7.park@...sung.com>,
        "jejb@...ux.ibm.com" <jejb@...ux.ibm.com>,
        "martin.petersen@...cle.com" <martin.petersen@...cle.com>,
        "asutoshd@...eaurora.org" <asutoshd@...eaurora.org>,
        "stanley.chu@...iatek.com" <stanley.chu@...iatek.com>,
        "cang@...eaurora.org" <cang@...eaurora.org>,
        "bvanassche@....org" <bvanassche@....org>,
        "tomas.winkler@...el.com" <tomas.winkler@...el.com>,
        ALIM AKHTAR <alim.akhtar@...sung.com>
Cc:     "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Sang-yoon Oh <sangyoon.oh@...sung.com>,
        Sung-Jun Park <sungjun07.park@...sung.com>,
        yongmyung lee <ymhungry.lee@...sung.com>,
        Jinyoung CHOI <j-young.choi@...sung.com>,
        Adel Choi <adel.choi@...sung.com>,
        BoRam Shin <boram.shin@...sung.com>
Subject: Re: [RFC PATCH v3 0/5] scsi: ufs: Add Host Performance Booster
 Support

On Mon, 2020-06-29 at 11:06 +0000, Avri Altman wrote:
> > 
> > Hi Avri
> > 
> > On Mon, 2020-06-29 at 05:24 +0000, Avri Altman wrote:
> > > Hi Bean,
> > > > 
> > > > Hi Daejun
> > > > 
> > > > Seems you intentionally ignored to give you comments on my
> > > > suggestion.
> > > > let me provide the reason.
> > > > 
> > > > Before submitting your next version patch, please check your
> > > > L2P
> > > > mapping HPB reqeust submission logical algorithem. I have did
> > > > performance comparison testing on 4KB, there are about 13%
> > > > performance
> > > > drop. Also the hit count is lower. I don't know if this is
> > > > related
> > > > to
> > > > your current work queue scheduling, since you didn't add the
> > > > timer
> > > > for
> > > > each HPB request.
> > > 
> > > In device control mode, the various decisions,
> > > and specifically those that are causing repetitive evictions,
> > > are made by the device.
> > > Is this the issue that you are referring to?
> > > 
> > 
> > For this device mode, if HPB mapping table of the active region
> > becomes
> > dirty in the UFS device side, there is repetitive inactive rsp, but
> > it
> > is not the reason for the condition I mentioned here.
> > 
> > > As for the driver, do you see any issue that is causing
> > > unnecessary
> > > latency?
> > > 
> > 
> > In Daejun's patch, it now uses work_queue, and as long there is new
> > RSP of
> > thesubregion to be activated, the driver will queue "work" to this
> > work
> > queue, actually, this is deferred work. we don't know when it will
> > be
> > scheduled/finished. we need to optimize it.
> 
> But those "to-do" lists are checked on every completion interrupt and
> on every resume.
> Do you see any scenario in which the "to-be-activated" or "to-be-
> inactivate" work is getting starved?
> 

let me run more testing cases, will back to you if there is new
updates.

Thanks,
Bean