Re: questions on NAPI processing latency and dropped network packets

[Chris Friesen]

Eric Dumazet wrote:
> Chris Friesen a Ãcrit :

> > Based on profiling and instrumentation it seems like the cost of 
> > sctp_endpoint_lookup_assoc() more than triples, which means that the 
> > amount of time that bottom halves are disabled in that function also 
> > triples.
>
> Any idea of the size of sctp hash size you have ?
> (your dmesg probably includes a message starting with SCTP: Hash tables 
> configured...
> How many concurrent sctp sockets are handled ?

Our lab is currently rebooting, but I'll try and get this once it's back up.

> Maybe sctp_assoc_hashfn() is too weak for your use, and some chains are 
> *really* long.

Based on the profiling information we're spending time in 
sctp_endpoint_lookup_assoc() which doesn't actually use hashes, so I 
can't see how the hash would be related.  I'm pretty new to SCTP though, 
so I may be missing something.

Here's the top results from readprofile, unfortunately these are 
aggregated across both cpus so they don't really show what's going on. 
The key thing is that sctp_endpoint_lookup_assoc() is the most expensive 
kernel routine on this entire system.

  3147 .power4_idle                              22.4786
  1712 .native_idle                              20.3810
  1234 .sctp_endpoint_lookup_assoc                2.1725
  1212 ._spin_unlock_irqrestore                   6.4468
   778 .do_futex                                  0.3791
   447 ._spin_unlock_irq                          4.2981
   313 .fget                                      1.7784
   277 .fput                                      3.8472
   275 .kfree                                     0.7473
   234 .__kmalloc                                 0.5571
   131 SystemCall_common                          0.3411
   130 .sctp_assoc_is_match                       0.6373
   123 .lock_sock                                 0.4155
   119 .find_vma                                  0.6919
   116 .kmem_cache_alloc                          0.3580
   111 .kmem_cache_free                           0.3343
   106 .skb_release_data                          0.4907
   102 .__copy_tofrom_user                        0.0724
   100 .exit_elf_binfmt                           1.9231
   100 .do_select                                 0.0820


Chris
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