Author: adrian
Date: Mon Jan 23 04:47:38 2017
New Revision: 312662
URL: https://svnweb.freebsd.org/changeset/base/312662
Log:
[ath] modify cabq and per-node packet usage limits.
* limit cabq to 64 - in practice if this stays at ath_txbuf then
all buffers can be tied up by a very busy broadcast domain (eg ARP
storm, way too much MDNS/NETBIOS). It's been like this in the
freebsd-wifi-build AP project for the longest time.
* Now that I figured out the hilarity inherent in aggregate forming
and AR9380 EDMA work, change the per-node to 64 frames by default.
I'll do some more work to shorten the queue latency introduced when
doing data so TCP isn't so terrible, but it's now no longer /always/
tens of milliseconds of extra latency when doing active iperf tests.
Notes:
The reason for the extra latency is partly tx/rx taskqueue handling and
scheduling, and partly due to a lack of airtime/QoS awareness of per-node
traffic. Ideally we'd have different limits/priorities on the QoS/TID
levels per node so say, voice/video data got a better share of buffer
allocations over best effort/bulk data, but we currently don't implement
that. It's not /hard/ to do, I just need to do it.
Tested:
* AR9380 (STA), AR9580 (hostap) - both with the relevant changes.
TCP is now at around 180mbit with rate control and RTS protection
enabled. UDP stays at 355mbit at MCS23, no HT protection.
Modified:
head/sys/dev/ath/if_ath.c
Modified: head/sys/dev/ath/if_ath.c
==============================================================================
--- head/sys/dev/ath/if_ath.c Mon Jan 23 04:30:08 2017 (r312661)
+++ head/sys/dev/ath/if_ath.c Mon Jan 23 04:47:38 2017 (r312662)
@@ -1028,12 +1028,16 @@ ath_attach(u_int16_t devid, struct ath_s
* otherwise) to be transmitted.
*/
sc->sc_txq_data_minfree = 10;
+
/*
- * Leave this as default to maintain legacy behaviour.
- * Shortening the cabq/mcastq may end up causing some
- * undesirable behaviour.
+ * Shorten this to 64 packets, or 1/4 ath_txbuf, whichever
+ * is smaller.
+ *
+ * Anything bigger can potentially see the cabq consume
+ * almost all buffers, starving everything else, only to
+ * see most fail to transmit in the given beacon interval.
*/
- sc->sc_txq_mcastq_maxdepth = ath_txbuf;
+ sc->sc_txq_mcastq_maxdepth = MIN(64, ath_txbuf / 4);
/*
* How deep can the node software TX queue get whilst it's asleep.
@@ -1041,11 +1045,10 @@ ath_attach(u_int16_t devid, struct ath_s
sc->sc_txq_node_psq_maxdepth = 16;
/*
- * Default the maximum queue depth for a given node
- * to 1/4'th the TX buffers, or 64, whichever
- * is larger.
+ * Default the maximum queue to to 1/4'th the TX buffers, or
+ * 64, whichever is smaller.
*/
- sc->sc_txq_node_maxdepth = MAX(64, ath_txbuf / 4);
+ sc->sc_txq_node_maxdepth = MIN(64, ath_txbuf / 4);
/* Enable CABQ by default */
sc->sc_cabq_enable = 1;
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