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Date:      Thu, 6 Sep 2018 08:35:35 +0200
From:      Marko Zec <zec@fer.hr>
To:        John-Mark Gurney <jmg@funkthat.com>
Cc:        Vincenzo Maffione <v.maffione@gmail.com>, <bz@freebsd.org>, Luigi Rizzo <rizzo@iet.unipi.it>, "freebsd-net@freebsd.org" <net@freebsd.org>
Subject:   Re: vale and netmap module questions
Message-ID:  <20180906083535.36ac39ce@x23>
In-Reply-To: <20180906004206.GB75530@funkthat.com>
References:  <20180901014953.GV45503@funkthat.com> <CA%2B_eA9gH_uzxV_YLBH1XdM-ygPUxXzD_W9_b45jTmeY-t0bQKg@mail.gmail.com> <20180901211123.GZ45503@funkthat.com> <20180904164303.68c43b6e@x23> <20180904162815.GA75530@funkthat.com> <CA%2B_eA9jp2rB0GjojNrbWuQJ3fChpF6U5KPOX-DvEzJDVzOSP4w@mail.gmail.com> <20180905104433.08ad13b8@x23> <CA%2B_eA9gxCrJXVFaooD4x491Ksff5=gomwfn0=E0X0_iuupuBHg@mail.gmail.com> <20180905124730.0f266c37@x23> <20180906004206.GB75530@funkthat.com>

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On Wed, 5 Sep 2018 17:42:06 -0700
John-Mark Gurney <jmg@funkthat.com> wrote:

> Marko Zec wrote this message on Wed, Sep 05, 2018 at 12:47 +0200:
> > On Wed, 5 Sep 2018 12:36:38 +0200
> > Vincenzo Maffione <v.maffione@gmail.com> wrote:
> >   
> > > Hi Marko,
> > >   Thanks a lot for identifying the problem.
> > > If I understand correctly, simply adding -D VIMAGE here
> > > https://github.com/luigirizzo/netmap/blob/master/sys/modules/netmap/Makefile#L11
> > > would at least mitigate the issue.
> > > If you think I'm right I'll just add it.  
> > 
> > Right, go for it...  
> 
> Why not just hook up netmap to the build?

I have no idea why it is on by default only on amd64...  Perhaps due to
the lack of adopters / testers on other platforms?  Perhaps the code has
some assumptions re. memory coherence model, or unaligned accesses,
which hold the water on amd64 but not necessarily elsewhere?

> Because if you add -DVIMAGE to the Makefile, you'll now break people
> who have kernels w/o VIMAGE..

No, and this is certifiable.  At least in this particular case, we have
only two macro instances which set / restore curvnet prior to calling
into the network stack.  If the network stack is of the non-VNET kind,
and thus doesn't care about curvnet, that won't do any harm.

> And the only reason to build netmap module manually is because it's not hooked up.

There's still a reason to retain the possibility to build netmap as
module, as this speeds up the development cycles for netmap-internal
hackers / experimenters.

But beyond that, running netmap without native support in device
drivers is pretty much pointless.



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