Date: Wed, 11 Mar 2015 18:17:35 +0300 From: Gleb Smirnoff <glebius@FreeBSD.org> To: John Baldwin <jhb@freebsd.org> Cc: svn-src-projects@freebsd.org, src-committers@freebsd.org Subject: Re: svn commit: r277122 - projects/ifnet/sys/dev/msk Message-ID: <20150311151735.GE17947@FreeBSD.org> In-Reply-To: <44632162.sBlScnaX0r@ralph.baldwin.cx> References: <201501130902.t0D927NE077024@svn.freebsd.org> <20150114144358.GD15484@FreeBSD.org> <20150306024101.GT17947@FreeBSD.org> <44632162.sBlScnaX0r@ralph.baldwin.cx>
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On Wed, Mar 11, 2015 at 10:08:30AM -0400, John Baldwin wrote:
J> > John, can you please look at this patch? It is against projects/ifnet.
J> >
J> > The idea is that if_snd_enqueue() tells us whether we grabbed to queue and
J> > own it or not. If we grabbed it, we go processing it to the end. However,
J> > we keep accounting on how many packets we processed there. If other
J> > producer notices that we processed too much, it will preempt the queue.
J> >
J> > Looks like a design that matches your demands. However, extra code needs
J> > to be put into drivers foo_start() functions, since now we need to disown
J> > the queue if we stop processing it for some reason different to queue getting
J> > empty.
J>
J> I think this patch is not a bad approach. It resembles the last thing I
J> posted to net@ except that you have added the burst length cap which is a
J> nice addition. Of course, this uses a lock to do so which buf_ring tries to
J> avoid.
J>
J> (I also eventually would love to have a way to move the enqueue out of drivers
J> entirely still where there is a callback for "drain this queue" that only
J> gets called in the !EBUSY case. I can't recall if that is compatible with your
J> stacking approach, but it would make it harder for drivers to get this wrong
J> if we can avoid duplicating it N times.)
I really wish to avoid duplicating code in regular drivers foo_transmit
and foo_start, but this doesn't seem easy for me.
Typical foo_transmit looks like:
if ((error = if_snd_enqueue(ifp, m)) != 0)
return (error);
* LOCK(sc);
* if (sc->link_not_active || sc->resources_not_allocated)
return;
* while (sc->tx_count <= DRIVER_CONST &&
(m = if_snd_dequeue(ifp)) != NULL) {
* if (driver_encap(sc, m, ...) != 0) {
if_snd_prepend(ifp, m);
break;
}
count++
}
if (count) {
* /* TX unit programming */
}
* UNLOCK(sc);
All lines marked with * are somewhat unique in drivers. So, cycle looks
a like, but always differ in details. Right now I don't have ideas how to
collapse that to a generic method. If anyone has, please share! :)
--
Totus tuus, Glebius.
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