[RFC PATCH net-next 0/6] Always use tx interrupt for virtio-net

From: Jason Wang
Date: Wed Oct 15 2014 - 03:44:02 EST

According to David, proper accounting and queueing (at all levels, not
just TCP sockets) is more important than trying to skim a bunch of
cycles by avoiding TX interrupts. Having an event to free the SKB is
absolutely essential for the stack to operate correctly.

This series tries to enable tx interrupt for virtio-net. The idea is
simple: enable tx interrupt and schedule a tx napi to free old xmit

Several notes:
- Tx interrupt storm avoidance when queue is about to be full is
kept. Since we may enable callbacks in both ndo_start_xmit() and tx
napi, patch 1 adds a check to make sure used event never go
back. This will let the napi not enable the callbacks wrongly after
delayed callbacks was used.
- For bulk dequeuing, there's no need to enable tx interrupt for each
packet. The last patch only enable tx interrupt for the final skb in
the chain through xmit_more and a new helper to publish current avail
idx as used event.

This series fixes several issues of original rfc pointed out by Michael.

Smoking test is done, and will do complete netperf test. Send the
seires for early review.


Jason Wang (6):
virtio: make sure used event never go backwards
virtio: introduce virtio_enable_cb_avail()
virtio-net: small optimization on free_old_xmit_skbs()
virtio-net: return the number of packets sent in free_old_xmit_skbs()
virtio-net: enable tx interrupt
virtio-net: enable tx interrupt only for the final skb in the chain

drivers/net/virtio_net.c | 125 ++++++++++++++++++++++++++++++------------
drivers/virtio/virtio_ring.c | 25 ++++++++-
include/linux/virtio.h | 2 +
3 files changed, 115 insertions(+), 37 deletions(-)

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