RX and NAPI.

diff --git a/15net/net b/15net/net
index 4e0b7e7..d64afd7 100644 (file)
--- a/15net/net
+++ b/15net/net
@@ -91,8 +91,53 @@
 * Current code already updates last time packet was transmitted
 * Driver should set watchdog\\_timeo and ndo\\_tx\\_timeout
 
+# Reception
+
+* Usually happens in an interrupt handler
+* Driver allocates skb: some drivers allocate it when setting up and arrange the
+  device to write into the buffers directly
+* Must set skb field protocol: easily done for ethernet drivers with
+  eth\\_type\\_trans
+* Finally, call netif\\_rx
+
+# NAPI
+
+* To allow more performance, NAPI introduces polling, avoiding too much
+  interrupts when load is high
+* Driver disables interrupts and enables polling in its interrupt handler
+  when RX happens
+* Network subsystem uses a softirq to do the polling
+* The driver poll function disables polling and reenabled interrupts when it's
+  done with its hardware queue
+
 # NAPI
 
+* struct napi\\_struct
+* netif\\_napi\\_add(dev, napi, poll\\_func, weight)
+* napi\\_enable: called in open
+* napi\\_disable: called in stop - awaits completion
+* napi\\_schedule
+       - napi\\_schedule\\_prep
+       - \\_\\_napi\\_schedule
+* napi\\_complete: called in poll when all is done
+* Use netif\\_receive\\_skb instead of netif\\_rx
+
+# NAPI step by step
+
+* In the interrupt handler:
+       - Checks that the interrupt received is RX
+       - Call napi\\_schedule\\_prep to check that napi isn't already scheduled
+       - Disable RX
+       - Call \\_\\_napi\\_schedule
+
+# Weight and Budget
+
+* The weight is the start budget for the interface, usually 16
+* The poll function must not dequeue more frames than the budget
+* It must call napi\\_complete if and only if it has exhausted the hardware
+  queues with less than the budget
+* It must return the number of entries in the queue processed
+
 # Changes in net device
 
 * Use netdev\\_priv, no priv anymore