Re: [Bloat] Marvell 385

[Dave Taht <dave.taht@gmail.com>]

On Sun, Aug 26, 2018 at 1:58 PM Rosen Penev <rosenp@gmail.com> wrote:
>
> On Sun, Aug 26, 2018 at 11:44 AM Mikael Abrahamsson <swmike@swm.pp.se> wrote:
> >
> > On Sat, 25 Aug 2018, Dave Taht wrote:
> >
> > > The expressobin is a Marvell Armada "3700LP (88F3720) dual core ARM
> > > Cortex A53 processor up to 1.2GHz" - how does that compare? I have
> > > plenty of ath10k and ath9k pcmcia cards....
> >
> > I have one of these, incl wifi. Right now the drivers are not in great
> > shape, but they're being worked on. My espressobin has worse performance
> > than on its wired ports than my WRT1200AC (Armada 385).
> If as you mentioned earlier that ethernet performance is limited by
> interrupts, then this commit is kind of depressing:
>
> https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/drivers/net/ethernet/marvell/mvneta.c?h=next-20180824&id=0f5c6c30a0f8c629b92ecdaef61b315c43fde10a

I was on that thread. It was broken before entirely. As for the single
interrupt on this chip variant - believe it or not, I'm not huge on
lots of different interrupts for everything. I'd like it if we had
more than an rx or tx interrupt
in general, I'd love it if we had a programmable "tx is almost done"
interrupt that you could tune to the
interrupt latency... and it's complicated and costs wires to have lots
of different interrupt types... and (fantasizing again) I'd love it if
we had a scratchpad or dedicated memory to store interrupt handlers in
rather than relying on cache....

I'd looked deeply into improving this driver once upon a time, and
wanted to rip the software gro out of it,
in particular, and not defer things as much, trying things like NAPI
of 16 and measuring where time was spent. The copy to memory is
expensive, and then it defers further work.

Less code, particularly near interrupt time, is better than a lot.
adding XMIT_MORE to the ar71xx driver (which hurt it badly) is one
example.

Given something *cool* now landing ( skb list batching, see lwn ) it
would be worthwhile to revisit this. I don't care if I get more
interrupts/sec (particularly on a multicore) if we could drain the rx
ring over smaller intervals...

but that's me, I'm all about the latency. :) Nobody's willing to rip
the latency out of stuff, they'd rather add features. It's really hard
to correctly measure interrupt latency regardless.


> >
> > I have talked to people who say the drivers are being worked on though...
> > If you have input, Kaloz is probably a great person to take that input. I
> > know other people working on Marvell drivers as well.
> >
> > --
> > Mikael Abrahamsson    email: swmike@swm.pp.se
> > _______________________________________________
> > Bloat mailing list
> > Bloat@lists.bufferbloat.net
> > https://lists.bufferbloat.net/listinfo/bloat



-- 

Dave Täht
CEO, TekLibre, LLC
http://www.teklibre.com
Tel: 1-669-226-2619