Changes between Version 14 and Version 15 of venice/ethernet

Timestamp:

08/30/2024 05:24:10 PM (3 weeks ago)

Author:

Tim Harvey

Comment:

added section on imx8m FEC ethernet coalesce

venice/ethernet

@@ -113 +113 @@
 * [https://ww1.microchip.com/downloads/en/Appnotes/AN3761-KSZ-DSA-Driver-Utilization-00003761A.pdf]
 
+
+== IMX8M FEC Ethernet Interrupt Coalesence
+The FEC Ethernet network interface controller on the IMX8MM and IMX8MP features interrupt coalesence which is enabled by default and increases packet latency for small numbers of packets.
+
+The purpose of the interrupt coalescing is to reduce the number of interrupts generated by the MAC so as to reduce the CPU loading.
+
+The default is to delay an RX and TX interrupt by 1ms or until 200 frames have occurred:
+{{{#!bash
+# ethtool --show-coalesce eth0
+Coalesce parameters for eth0:
+Adaptive RX: off  TX: off
+stats-block-usecs: 0
+sample-interval: 0
+pkt-rate-low: 0
+pkt-rate-high: 0
+
+rx-usecs: 1000
+rx-frames: 200
+rx-usecs-irq: 0
+rx-frames-irq: 0
+
+tx-usecs: 1000
+tx-frames: 200
+tx-usecs-irq: 0
+tx-frames-irq: 0
+
+rx-usecs-low: 0
+rx-frames-low: 0
+tx-usecs-low: 0
+tx-frames-low: 0
+
+rx-usecs-high: 0
+rx-frames-high: 0
+tx-usecs-high: 0
+tx-frames-high: 0
+}}}
+
+This would cause a packet latency of >1ms for light network activity.
+
+This can be modified using the userspace 'ethtool':
+{{{#!bash
+# default is 1000us 200 frames, change to 1/1
+ethtool --coalesce eth0 tx-usecs 1
+ethtool --coalesce eth0 tx-frames 1
+ethtool --coalesce eth0 rx-usecs 1
+ethtool --coalesce eth0 rx-frames 1
+}}}
+ - ping times now will be < 0.5ms
+
+And if you wanted to change it back to defaults for example:
+{{{#!bash
+# change back to default
+ethtool --coalesce eth0 tx-usecs 1000
+ethtool --coalesce eth0 tx-frames 200
+ethtool --coalesce eth0 rx-usecs 1000
+ethtool --coalesce eth0 rx-frames 200
+}}}
+ - ping times now will be >1ms
+