When using bnx2 in a high transmit load, bnx2_tx_int() cost is pretty high.
There are two reasons.
One is an expensive call to bnx2_get_hw_tx_cons(bnapi) for each freed skb
One is cpu stalls when accessing skb_is_gso(skb) / skb_shinfo(skb)->nr_frags
because of two cache line misses.
(One to get skb->end/head to compute skb_shinfo(skb),
one to get is_gso/nr_frags)
This patch :
1) avoids calling bnx2_get_hw_tx_cons(bnapi) too many times.
2) makes bnx2_start_xmit() cache is_gso & nr_frags into sw_tx_bd descriptor.
This uses a litle bit more ram (256 longs per device on x86), but helps a lot.
3) uses a prefetch(&skb->end) to speedup dev_kfree_skb(), bringing
cache line that will be needed in skb_release_data()
result is 5 % bandwidth increase in benchmarks, involving UDP or TCP receive
& transmits, when a cpu is dedicated to ksoftirqd for bnx2.
bnx2_tx_int going from 3.33 % cpu to 0.5 % cpu in oprofile
Note : skb_dma_unmap() still very expensive but this is for another patch,
not related to bnx2 (2.9 % of cpu, while it does nothing on x86_32)
Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Eric Dumazet
d62fda082c