AR9287 interrupt rate

[sirok]

 Hi!

ath0: <Atheros 9287> mem 0xfe500000-0xfe50ffff irq 16 at device 0.0 on pci1
ath0: [HT] enabling HT modes
ath0: [HT] enabling short-GI in 20MHz mode
ath0: [HT] 1 stream STBC receive enabled
ath0: [HT] 1 stream STBC transmit enabled
ath0: [HT] 2 RX streams; 2 TX streams
ath0: AR9287 mac 384.2 RF5133 phy 15.15
ath0: 2GHz radio: 0x0000; 5GHz radio: 0x00c0

ath0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 2290
        ether 20:7c:8f:xx:xx:xx
        nd6 options=29<PERFORMNUD,IFDISABLED,AUTO_LINKLOCAL>
        media: IEEE 802.11 Wireless Ethernet autoselect mode 11ng <hostap>
        status: running

wlan0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
        ether 20:7c:8f:xx:xx:xx
        inet 192.168.x.1 netmask 0xffffff00 broadcast 192.168.x.255
        inet6 fe80::xxxxx%wlan0 prefixlen 64 scopeid 0x13
        inet6 xxxxx::1 prefixlen 64
        nd6 options=21<PERFORMNUD,AUTO_LINKLOCAL>
        media: IEEE 802.11 Wireless Ethernet autoselect mode 11ng <hostap>
        status: running
        ssid XXXXX channel 6 (2437 MHz 11g ht/40+) bssid 20:7c:8f:xx:xx:xx
        regdomain NONE country RU indoor ecm authmode WPA2/802.11i
        privacy MIXED deftxkey 2 AES-CCM 2:128-bit AES-CCM 3:128-bit
        txpower 20 scanvalid 60 protmode CTS ampdulimit 64k ampdudensity 8
        shortgi wme burst dtimperiod 1 -dfs

Problem description

Just after reboot vmstat -i shows about 60 interrupts/sec
irq16: ath0                        40558         66

But after some time (a few hours I think) irq rate starts to rise slowly.
After ~ 23 hours:
irq16: ath0                  12086600069     146845
After 23h+5 minutes:
irq16: ath0                  12154198114     147131
About 10 minutes later:
irq16: ath0                  12307854569     147771
Now:
irq16: ath0                  14089141951     154492

And so on up to about 280000/sec. AP mode stops functioning at some point.
It's a pretty old problem. However on older revs irq goes high immediately after boot, even if ath is not configured at all.

HEAD rev 253412

Thank you!

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