Re: [PATCH net-next 17/20] tcp: defer skb freeing after socket lock is released

On Tue, 16 Nov 2021 07:22:02 -0800 Eric Dumazet wrote:

Here is the perf top profile on cpu used by user thread doing the
recvmsg(), at 96 Gbit/s

We no longer see skb freeing related costs, but we still see costs of
having to process the backlog.

   81.06%  [kernel]       [k] copy_user_enhanced_fast_string
     2.50%  [kernel]       [k] __skb_datagram_iter
     2.25%  [kernel]       [k] _copy_to_iter
     1.45%  [kernel]       [k] tcp_recvmsg_locked
     1.39%  [kernel]       [k] tcp_rcv_established

Huh, somehow I assumed your 4k MTU numbers were with zero-copy :o

Out of curiosity - what's the softirq load with 4k? Do you have an 
idea what the load is on the CPU consuming the data vs the softirq
processing with 1500B ?