commit 28cc0c295c957f68a6e8afbac62d0e50d56ccb25 Author: Sepherosa Ziehau <se...@dragonflybsd.org> Date: Sun Dec 23 20:31:32 2012 +0800
ifq/staging: Initial implementation of IFQ packet staging mechanism The packets enqueued into IFQ are staged to a certain amount before the ifnet's if_start is called. In this way, the driver could avoid writing to hardware registers upon every packet, instead, hardware registers could be written when certain amount of packets are put onto hardware TX ring. The measurement on several modern NICs (emx(4), igb(4), bnx(4), bge(4), jme(4)) shows that the hardware registers writing aggregation could save ~20% CPU time when 18bytes UDP datagrams are transmitted at 1.48Mpps. IFQ packets staging is performed for direct ifnet's if_start calling, i.e. ifq_try_ifstart() IFQ packets staging will be stopped upon any of the following conditions: - If the count of packets enqueued on the current CPU is great than or equal to ifq_stage_cntmax. - If the total length of packets enqueued on the current CPU is great than or equal to the hardware's MTU - max_protohdr. max_protohdr is cut from the hardware's MTU mainly bacause a full TCP segment's size is usually less than hardware's MTU. - if_start interlock (if_snd.altq_started) is not released. - The if_start_rollup(), which is registered as low priority netisr rollup function, is called; probably because no more work is pending for netisr. Currently IFQ packet staging is only performed in netisr threads. Inspired-by: Luigi Rizzo's netmap paper (http://info.iet.unipi.it/~luigi/netmap/) Also-Suggested-by: dillon@ Summary of changes: sys/net/altq/if_altq.h | 13 +++ sys/net/if.c | 195 +++++++++++++++++++++++++++++++++++++---------- 2 files changed, 166 insertions(+), 42 deletions(-) http://gitweb.dragonflybsd.org/dragonfly.git/commitdiff/28cc0c295c957f68a6e8afbac62d0e50d56ccb25 -- DragonFly BSD source repository