[Cerowrt-devel] [Codel] hardware hacking on fq_codel in FPGA form at 10GigE
dwmw2 at infradead.org
Fri Dec 21 16:54:03 EST 2012
On Fri, 2012-12-21 at 13:45 -0500, Jim Gettys wrote:
> I've been working with blogic (John Crispin) on debloating the Lantiq
> driver, which we are trying to test; since it is entirely open source. In
> the Lantiq DSL driver case, the hardware sprouted exactly the same sort of
> transmit/receive rings found in ethernet drivers, with the corresponding
> bufferbloat due to device drivers being totally stupid. Unfortunately, BQL
> is ethernet only, and right now doesn't work properly at low bandwidths.
Hmmm. With the code that's currently in OpenWRT, we shouldn't *let* the
ATM driver have a huge queue of packets unless it's doing something
egregiously stupid like calling the vcc->pop() function on the skb
before it's actually sent it.
PPPoATM for a long time has limited the queue at the hardware driver to
2 packets, instead of a full sock_wmem's worth of buffers like it used
to in the past. Since a couple of weeks ago the BR2684 driver
(Ether-over-ATM, as used with PPPoE on top) also does the same thing.
So the ATM driver would have to go out of its way to screw you over¹.
Btw, I'm looking at ways to *make* BQL on the PPP netdev work properly,
tracking packets all the way to the wire even when it's PPPoA,
PPPoE(oA), L2TP or whatever.
¹ Unless you're using IP over ATM directly. I haven't looked at that one.
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