netdev - Re: [EXT] Re: [PATCH v12 net-next 12/15] net: mvpp2: add BM protection underrun feature support

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Date:   Fri, 12 Feb 2021 14:52:52 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Marcin Wojtas <mw@...ihalf.com>
Cc:     Stefan Chulski <stefanc@...vell.com>,
        David Miller <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "thomas.petazzoni@...tlin.com" <thomas.petazzoni@...tlin.com>,
        Nadav Haklai <nadavh@...vell.com>,
        Yan Markman <ymarkman@...vell.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "linux@...linux.org.uk" <linux@...linux.org.uk>,
        "rmk+kernel@...linux.org.uk" <rmk+kernel@...linux.org.uk>,
        "atenart@...nel.org" <atenart@...nel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "sebastian.hesselbarth@...il.com" <sebastian.hesselbarth@...il.com>,
        "gregory.clement@...tlin.com" <gregory.clement@...tlin.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [EXT] Re: [PATCH v12 net-next 12/15] net: mvpp2: add BM
 protection underrun feature support

> > Or we have also found out, that pushing back on parameters like this,
> > the developers goes back and looks at the code, and sometimes figures
> > out a way to automatically do the right thing, removing the
> > configuration knob, and just making it all simpler for the user to
> > use.
> 
> I think of 2 alternatives:
> * `ethtool --set-priv-flags` - in such case there is a question if
> switching this particular feature in runtime is a good idea.
> * New DT/ACPI property - it is a hardware feature after all, so maybe
> let the user decide whether to enable it on the platform description
> level.

Does this even need to be configurable? What is the cost of turning it
on? How does having less pools affect the system? Does average latency
go up?  When would i consider an underrun actually a good thing?

Maybe it should just be hard coded on? Or we should try to detect when
underruns are happening a lot, and dynamically turn it on for a while?

	  Andrew