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Date:   Mon, 1 Feb 2021 09:44:18 +0100
From:   "gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>
To:     Avri Altman <Avri.Altman@wdc.com>
Cc:     "daejun7.park@samsung.com" <daejun7.park@samsung.com>,
        "James E . J . Bottomley" <jejb@linux.vnet.ibm.com>,
        "Martin K . Petersen" <martin.petersen@oracle.com>,
        "linux-scsi@vger.kernel.org" <linux-scsi@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Bart Van Assche <bvanassche@acm.org>,
        yongmyung lee <ymhungry.lee@samsung.com>,
        ALIM AKHTAR <alim.akhtar@samsung.com>,
        "asutoshd@codeaurora.org" <asutoshd@codeaurora.org>,
        Zang Leigang <zangleigang@hisilicon.com>,
        Avi Shchislowski <Avi.Shchislowski@wdc.com>,
        Bean Huo <beanhuo@micron.com>,
        "cang@codeaurora.org" <cang@codeaurora.org>,
        "stanley.chu@mediatek.com" <stanley.chu@mediatek.com>
Subject: Re: [PATCH 3/8] scsi: ufshpb: Add region's reads counter
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On Mon, Feb 01, 2021 at 08:17:59AM +0000, Avri Altman wrote:
> > 
> > On Mon, Feb 01, 2021 at 07:51:19AM +0000, Avri Altman wrote:
> > > >
> > > > On Mon, Feb 01, 2021 at 07:12:53AM +0000, Avri Altman wrote:
> > > > > > > +#define WORK_PENDING 0
> > > > > > > +#define ACTIVATION_THRSHLD 4 /* 4 IOs */
> > > > > > Rather than fixing it with macro, how about using sysfs and make it
> > > > > > configurable?
> > > > > Yes.
> > > > > I will add a patch making all the logic configurable.
> > > > > As all those are hpb-related parameters, I think module parameters are
> > > > more adequate.
> > > >
> > > > No, this is not the 1990's, please never add new module parameters to
> > > > drivers.  If not for the basic problem of they do not work on a
> > > > per-device basis, but on a per-driver basis, which is what you almost
> > > > never want.
> > > OK.
> > >
> > > >
> > > > But why would you want to change this value, why can't the driver "just
> > > > work" and not need manual intervention?
> > > It is.
> > > But those are a knobs each vendor may want to tweak,
> > > So it'll be optimized with its internal device's implementation.
> > >
> > > Tweaking the parameters, as well as the entire logic, is really an endless
> > task.
> > > Some logic works better for some scenarios, while falling behind on others.
> > 
> > Shouldn't the hardware know how to handle this dynamically?  If not, how
> > is a user going to know?
> There is one "brain".
> It is either in the device - in device mode, Or in the host - in host mode control.
> The "brain" decides which region is active, thus carrying the physical address along with the logical -
> minimizing context switches in the device's RAM.
> 
> There can be up to N active regions.
> Activation and deactivation has its overhead.
> So basically it is a constraint-optimization problem.

So how do you solve it?  And how would you expect a user to solve it if
the kernel can not?

You better document the heck out of these configuration options :)

thanks,

greg k-h