Re: [PATCH net-next 14/15 v2] net: Reference bpf_redirect_info via task_struct on PREEMPT_RT.

[Sebastian Andrzej Siewior <bigeasy@linutronix.de>]

On 2024-05-14 14:20:03 [+0200], Jesper Dangaard Brouer wrote:
> Trick for CPU-map to do early drop on remote CPU:
> 
>  # ./xdp-bench redirect-cpu --cpu 3 --remote-action drop ixgbe1
> 
> I recommend using Ctrl+\ while running to show more info like CPUs being
> used and what kthread consumes.  To catch issues e.g. if you are CPU
> redirecting to same CPU as RX happen to run on.

Okay. So I reworked the last two patches make the struct part of
task_struct and then did as you suggested:

Unpatched:
|Sending:
|Show adapter(s) (eno2np1) statistics (ONLY that changed!)
|Ethtool(eno2np1 ) stat:    952102520 (    952,102,520) <= port.tx_bytes /sec
|Ethtool(eno2np1 ) stat:     14876602 (     14,876,602) <= port.tx_size_64 /sec
|Ethtool(eno2np1 ) stat:     14876602 (     14,876,602) <= port.tx_unicast /sec
|Ethtool(eno2np1 ) stat:    446045897 (    446,045,897) <= tx-0.bytes /sec
|Ethtool(eno2np1 ) stat:      7434098 (      7,434,098) <= tx-0.packets /sec
|Ethtool(eno2np1 ) stat:    446556042 (    446,556,042) <= tx-1.bytes /sec
|Ethtool(eno2np1 ) stat:      7442601 (      7,442,601) <= tx-1.packets /sec
|Ethtool(eno2np1 ) stat:    892592523 (    892,592,523) <= tx_bytes /sec
|Ethtool(eno2np1 ) stat:     14876542 (     14,876,542) <= tx_packets /sec
|Ethtool(eno2np1 ) stat:            2 (              2) <= tx_restart /sec
|Ethtool(eno2np1 ) stat:            2 (              2) <= tx_stopped /sec
|Ethtool(eno2np1 ) stat:     14876622 (     14,876,622) <= tx_unicast /sec
|
|Receive:
|eth1->?                 8,732,508 rx/s                  0 err,drop/s
|  receive total         8,732,508 pkt/s                 0 drop/s                0 error/s
|    cpu:10              8,732,508 pkt/s                 0 drop/s                0 error/s
|  enqueue to cpu 3      8,732,510 pkt/s                 0 drop/s             7.00 bulk-avg
|    cpu:10->3           8,732,510 pkt/s                 0 drop/s             7.00 bulk-avg
|  kthread total         8,732,506 pkt/s                 0 drop/s          205,650 sched
|    cpu:3               8,732,506 pkt/s                 0 drop/s          205,650 sched
|    xdp_stats                   0 pass/s        8,732,506 drop/s                0 redir/s
|      cpu:3                     0 pass/s        8,732,506 drop/s                0 redir/s
|  redirect_err                  0 error/s
|  xdp_exception                 0 hit/s

I verified that the "drop only" case hits 14M packets/s while this
redirect part reports 8M packets/s.

Patched:
|Sending:
|Show adapter(s) (eno2np1) statistics (ONLY that changed!)
|Ethtool(eno2np1 ) stat:    952635404 (    952,635,404) <= port.tx_bytes /sec
|Ethtool(eno2np1 ) stat:     14884934 (     14,884,934) <= port.tx_size_64 /sec
|Ethtool(eno2np1 ) stat:     14884928 (     14,884,928) <= port.tx_unicast /sec
|Ethtool(eno2np1 ) stat:    446496117 (    446,496,117) <= tx-0.bytes /sec
|Ethtool(eno2np1 ) stat:      7441602 (      7,441,602) <= tx-0.packets /sec
|Ethtool(eno2np1 ) stat:    446603461 (    446,603,461) <= tx-1.bytes /sec
|Ethtool(eno2np1 ) stat:      7443391 (      7,443,391) <= tx-1.packets /sec
|Ethtool(eno2np1 ) stat:    893086506 (    893,086,506) <= tx_bytes /sec
|Ethtool(eno2np1 ) stat:     14884775 (     14,884,775) <= tx_packets /sec
|Ethtool(eno2np1 ) stat:           14 (             14) <= tx_restart /sec
|Ethtool(eno2np1 ) stat:           14 (             14) <= tx_stopped /sec
|Ethtool(eno2np1 ) stat:     14884937 (     14,884,937) <= tx_unicast /sec
|
|Receive:
|eth1->?                 8,735,198 rx/s                  0 err,drop/s
|  receive total         8,735,198 pkt/s                 0 drop/s                0 error/s
|    cpu:6               8,735,198 pkt/s                 0 drop/s                0 error/s
|  enqueue to cpu 3      8,735,193 pkt/s                 0 drop/s             7.00 bulk-avg
|    cpu:6->3            8,735,193 pkt/s                 0 drop/s             7.00 bulk-avg
|  kthread total         8,735,191 pkt/s                 0 drop/s          208,054 sched
|    cpu:3               8,735,191 pkt/s                 0 drop/s          208,054 sched
|    xdp_stats                   0 pass/s        8,735,191 drop/s                0 redir/s
|      cpu:3                     0 pass/s        8,735,191 drop/s                0 redir/s
|  redirect_err                  0 error/s
|  xdp_exception                 0 hit/s

This looks to be in the same range/ noise level. top wise I have
ksoftirqd at 100% and cpumap/./map at ~60% so I hit CPU speed limit on a
10G link. perf top shows
|   18.37%  bpf_prog_4f0ffbb35139c187_cpumap_l4_hash         [k] bpf_prog_4f0ffbb35139c187_cpumap_l4_hash
|   13.15%  [kernel]                                         [k] cpu_map_kthread_run
|   12.96%  [kernel]                                         [k] ixgbe_poll
|    6.78%  [kernel]                                         [k] page_frag_free
|    5.62%  [kernel]                                         [k] xdp_do_redirect

for the top 5. Is this something that looks reasonable?

Sebastian