netdev - Re: [RFC 02/11] Add RoCE driver framework

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Date:   Wed, 14 Sep 2016 08:15:23 +0000
From:   "Mintz, Yuval" <Yuval.Mintz@...ium.com>
To:     Leon Romanovsky <leon@...nel.org>
CC:     Yuval Mintz <Yuval.Mintz@...gic.com>,
        Mark Bloch <markb@...lanox.com>,
        Ram Amrani <Ram.Amrani@...gic.com>,
        "dledford@...hat.com" <dledford@...hat.com>,
        David Miller <davem@...emloft.net>,
        Ariel Elior <Ariel.Elior@...gic.com>,
        Michal Kalderon <Michal.Kalderon@...gic.com>,
        Rajesh Borundia <rajesh.borundia@...gic.com>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>
Subject: Re: [RFC 02/11] Add RoCE driver framework

> > >> >> +uint debug;
> > >> >> +module_param(debug, uint, 0);
> > > >>> +MODULE_PARM_DESC(debug, "Default debug msglevel");
> > >>
> > >> >Why are you adding this as a module parameter?
> > >>
> > >>  I believe this is mostly to follow same line as qede which also defines
> > > > 'debug' module parameter for allowing easy user control of debug
> > > > prints [& specifically for probe prints, which can't be controlled
> > > > otherwise].
> >
> > > Can you give us an example where dynamic debug and tracing infrastructures
> > > are not enough?
> >
> > > AFAIK, most of these debug module parameters are legacy copy/paste
> > > code which is useless in real life scenarios.
> >
> > Define 'enough'; Using dynamic debug you can provide all the necessary
> > information and at an even better granularity that's achieved by suggested
> > infrastructure,  but is harder for an end-user to use. Same goes for tracing.
> >
> > The 'debug' option provides an easy grouping for prints related to a specific
> > area in the driver.
> 
> It is hard to agree with you that user which knows how-to load modules
> with parameters won't success to enable debug prints.

I think you're giving too much credit to the end-user. :-D

> In addition, global increase in debug level for whole driver will create
> printk storm in dmesg and give nothing to debuggability.

So basically, what you're claiming is that ethtool 'msglvl' setting for devices
is completely obselete. While this *might* be true, we use it extensively
in our qede and qed drivers; The debug module parameter merely provides
a manner of setting the debug value prior to initial probe for all interfaces.
qedr follows the same practice.