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SubjectRe: simple mod_timer patch


Andrew Morton wrote:
> Steve Modica <modica@sgi.com> wrote:
>
>>I pulled this back from the 2.6 kernel to reduce some serious contention on the
>>timerlist_lock when I had 8 gigabit cards runnings.
>>
>
> By how much did it reduce contention?


I got some profile results on the recv side for a 64p system running 8 recv
threads using 1500 byte frames and the 1.5 tg3 driver (with NAPI)

The 4 cpus I was using were pegged.. Here's the sorted profile useage:

23581672 total 3.7362
22193477 cpu_idle 43346.6348
282048 tg3_poll 275.4375
218033 mod_timer 272.5412
158467 __copy_user 66.9202
71956 sn_gettimeoffset 249.8472
60643 tcp_v4_rcv 11.8443
59058 tcp_rcv_established 9.5625
42402 kmalloc 31.5491
41140 alloc_skb 33.8322
38985 __kfree_skb 46.8570
36601 skb_release_data 81.6987
31168 kfree 57.2941
24531 __wake_up 45.0938
22551 kmem_cache_alloc 19.0465

Here's an 8 cpu run (1 cpu per interface):


35664353 cpu_idle 69656.9395
> > 550978 mod_timer 688.7225
> > 141781 sn_gettimeoffset 492.2951
> > 428917 tg3_poll 418.8643
> > 310004 __copy_user 130.9139
> > 50981 skb_release_data 113.7969
> > 30982 do_gettimeofday 74.4760
> > 52091 __kfree_skb 62.6094
> > 25806 kfree 47.4375
> > 36212 tcp_v4_do_rcv 37.7208
> > 44090 alloc_skb 36.2582
> > 11238 tg3_recycle_rx 35.1187


Here's a run with 8 cards receiving, 4 interrupt cpus with the mod_timer fix and
a change so the stack isn't time stamping every packet (it's sorted based on the
weighted load, but mod_timer had just dropped way down into the noise for these
runs.)

[root@ascender2 modica]# head profile.recv.1500
40057535 cpu_idle 78237.3730
228061 tg3_poll 222.7158
36780 skb_release_data 82.0982
13100 pciio_dmatrans_addr 81.8750
39542 __wake_up 72.6875
4494 ia64_page_valid 70.2188
35029 kfree 64.3915
140595 __copy_user 59.3729
16307 __release_sock 46.3267
18897 kmem_cache_free 45.4255



--
Steve Modica
work: 651-683-3224
MTS-Technical Lead
"Give a man a fish, and he will eat for a day, hit him with a fish and
he leaves you alone" - me

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