David Miller wrote:
From: Vladislav Bolkhovitin <vst@xxxxxxxx>
Date: Wed, 13 Aug 2008 22:35:34 +0400
This is because the target sends data in a zero-copy manner, so its
CPU is capable to deal with the load, but on the initiator there are
additional data copies from skb's to page cache and from page cache
to application.
If you've actually been reading at all what I've been saying in this
thread you'll see that I've described a method to do this copy
avoidance in a completely stateless manner.
You don't need to implement a TCP stack in the card in order to do
data placement optimizations. They can be done completely stateless.
Sure, I read what you wrote before writing (although, frankly, didn't
get the idea). But I don't think that overall it would be as efficient
as full hardware offload. See my reply to Jeff Garzik about that.
Also, large portions of the cpu overhead are transactional costs,
which are significantly reduced by existing technologies such as
LRO.
The test used Myricom Myri-10G cards (myri10ge driver), which support
LRO. And from ethtool -S output I conclude it was enabled. Just in case,
I attached it, so you can recheck me.
Thus, apparently, LRO doesn't make a fundamental difference. Maybe this
particular implementation isn't too efficient, I don't know. I don't
have enough information for that.
Vlad
NIC statistics:
rx_packets: 471090527
tx_packets: 175404246
rx_bytes: 683684492944
tx_bytes: 636200696592
rx_errors: 0
tx_errors: 0
rx_dropped: 0
tx_dropped: 0
multicast: 0
collisions: 0
rx_length_errors: 0
rx_over_errors: 0
rx_crc_errors: 0
rx_frame_errors: 0
rx_fifo_errors: 0
rx_missed_errors: 0
tx_aborted_errors: 0
tx_carrier_errors: 0
tx_fifo_errors: 0
tx_heartbeat_errors: 0
tx_window_errors: 0
rx_skbs: 0
alloc_order: 0
builtin_fw: 0
napi: 1
tx_boundary: 4096
WC: 2
irq: 1268
MSI: 1
MSIX: 0
read_dma_bw_MBs: 1575
write_dma_bw_MBs: 1375
read_write_dma_bw_MBs: 2406
serial_number: 320283
watchdog_resets: 0
link_changes: 2
link_up: 1
dropped_link_overflow: 0
dropped_link_error_or_filtered: 0
dropped_pause: 0
dropped_bad_phy: 0
dropped_bad_crc32: 0
dropped_unicast_filtered: 0
dropped_multicast_filtered: 0
dropped_runt: 0
dropped_overrun: 0
dropped_no_small_buffer: 0
dropped_no_big_buffer: 479
----------- slice ---------: 0
tx_pkt_start: 176354843
tx_pkt_done: 176354843
tx_req: 474673372
tx_done: 474673372
rx_small_cnt: 19592127
rx_big_cnt: 462319631
wake_queue: 0
stop_queue: 0
tx_linearized: 0
LRO aggregated: 481899984
LRO flushed: 43071334
LRO avg aggr: 11
LRO no_desc: 0
