Re: Measuring tools - top and interrupts

[Mike Galbraith <efault@gmx.de>]

On Thu, 2006-06-22 at 16:37 -0700, Danial Thom wrote:
> I'm sorry, but you're being an idiot if you think
> that 16K interrupts per second and forwarding 75K
> pps generate no cpu load. Its just that simple.
> It also means that you've never profiled a kernel
> because you don't understand where the loads are
> generated. You've probably been on too many lists
> with too many people who have no idea what
> they're talking about.

(what horrid manners)

Hm.  You may be right about the load average calculation being broken.

Below is a 100 second profile sample of my 3GHz P4 handling 15K
interrupts per second while receiving a flood ping.  My interpretation
is that tools should be showing ~10% cpu load rather than zero.  Am I'm
misinterpreting it?

 97574 total                                      0.0258
 89549 default_idle                             1017.6023
  1734 ioread16                                  36.8936
  1138 ioread8                                   24.7391
   974 rhine_start_tx                             1.3994
   534 __do_softirq                               3.8417
   331 handle_IRQ_event                           3.2772
   223 rhine_interrupt                            0.0739
   222 memset                                     7.9286
   194 nf_iterate                                 1.5520
   140 local_bh_enable                            1.0769
    99 __kmalloc                                  1.0532
    92 net_rx_action                              0.2000
    85 kfree                                      0.9884
    82 skb_release_data                           0.6406
    77 csum_partial_copy_generic                  0.3105
    73 ip_push_pending_frames                     0.0681
    71 __alloc_skb                                0.2898
    69 kmem_cache_free                            1.3529
    66 kmem_cache_alloc                           1.3750
    62 csum_partial                               0.2153
    61 rt_hash_code                               0.4959
    61 ip_append_data                             0.0253
    60 netif_receive_skb                          0.0516
    58 ip_rcv                                     0.0471
    58 ip_local_deliver                           0.0854
    58 eth_type_trans                             0.2489
    55 ip_output                                  0.0957
    52 icmp_reply                                 0.1187