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On DWMAC3 and later, there's a RX Watchdog interrupt that's used for
interrupt coalescing. It's known to be buggy on some platforms, and
dwmac-socfpga appears to be one of them. Changing the interrupt
coalescing from ethtool doesn't appear to have any effect here.
Without disabling RIWT (Received Interrupt Watchdog Timer, I
believe...), we observe latencies while receiving traffic that amount to
around ~0.4ms. This was discovered with NTP but can be easily reproduced
with a simple ping. Without this patch :
64 bytes from 192.168.5.2: icmp_seq=1 ttl=64 time=0.657 ms
With this patch :
64 bytes from 192.168.5.2: icmp_seq=1 ttl=64 time=0.254 ms
Fixes:
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| .. | ||
| stmmac | ||
| Kconfig | ||
| Makefile | ||