netdev - RE: [PATCH] qede: fix CONFIG_INFINIBAND

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Date:   Thu, 13 Oct 2016 10:44:36 +0000
From:   "Mintz, Yuval" <Yuval.Mintz@...ium.com>
To:     Arnd Bergmann <arnd@...db.de>
CC:     Ariel Elior <Ariel.Elior@...gic.com>,
        "everest-linux-l2@...gic.com" <everest-linux-l2@...gic.com>,
        Alexander Duyck <aduyck@...antis.com>,
        "Amrani, Ram" <Ram.Amrani@...ium.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>
Subject: RE: [PATCH] qede: fix CONFIG_INFINIBAND_QEDR=m build error

> > > > While I don't mind, you could have argued is that we're not
> > > > removing enough, not too much.
> > > > I.e., perhaps the rdma_msix_* fields should also have been
> > > > ifdef-ed instead. [in which case this solution would not have
> > > > worked]
> > >
> > > That would add even more #ifdefs though.
> >
> > I agree. Although I'm never clear on the guidelines for the tradeoff -
> > How much memory/code is considered too much so that you'd have To
> > ifdef code out instead of 'wasting'?
> > [I obviously don't claim 64 bytes of memory hit that threshold]
> 
> I don't think code size should ever be a reason for an #ifdef in a .c
> file: if the code is well-structured, you can always get the same object code
> using if(IS_ENABLED()) checks within the code at better readability or better
> compile-time coverage.
> 
> Between if(IS_ENABLED()) checks and inline helpers, it usually doesn't matter
> much either way as long as the separation between the modules is clear enough.
> In the example above, removing the structure fields however would require to
> move the debugging output into another inline function though.

Still, the question remains - If we were to allocate X bytes of memory
per-something [in this case, per qed owned PCI function], and that memory
wouldn't be functional without a some CONFIG option enabled,
how big should X become before we'd decide the fields should also be
dependent on the option?
It bears no real relevance to this case, as the fields involved are insignificantly
small. But still - is there a rule of thumb here?

> > BTW, are you interested in doing a v2 for this? Or would you prefer if
> > we'd pick it up from here?
> 
> I think it's better if you do a v2, as you better understand the long-term plans. I'd
> be happy to test your patch in my randconfig build setup if you like.

Sure.