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Date: Sun, 01 Mar 2009 18:03:12 +0100 From: Eric Dumazet <dada1@...mosbay.com> To: Kenny Chang <kchang@...enacr.com> CC: netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>, Christoph Lameter <cl@...ux-foundation.org> Subject: Re: Multicast packet loss Eric Dumazet a écrit : > Kenny Chang a écrit : >> It's been a while since I updated this thread. We've been running >> through the different suggestions and tabulating their effects, as well >> as trying out an Intel card. The short story is that setting affinity >> and MSI works to some extent, and the Intel card doesn't seem to change >> things significantly. The results don't seem consistent enough for us >> to be able to point to a smoking gun. >> >> It does look like the 2.6.29-rc4 kernel performs okay with the Intel >> card, but this is not a real-time build and it's not likely to be in a >> supported Ubuntu distribution real soon. We've reached the point where >> we'd like to look for an expert dedicated to work on this problem for a >> period of time. The final result being some sort of solution to produce >> a realtime configuration with a reasonably "aged" kernel (.24~.28) that >> has multicast performance greater than or equal to that of 2.6.15. >> >> If anybody is interested in devoting some compensated time to this >> issue, we're offering up a bounty: >> http://www.athenacr.com/bounties/multicast-performance/ >> >> For completeness, here's the table of our experiment results: >> >> ====================== ================== ========= ========== >> =============== ============== ============== ================= >> Kernel flavor IRQ affinity *4x >> mcasttest* *5x mcasttest* *6x mcasttest* *Mtools2* [4]_ >> ====================== ================== ========= ========== >> =============== ============== ============== ================= >> Intel >> e1000e >> >> -----------------------------------------+---------+----------+---------------+--------------+--------------+----------------- >> >> 2.6.24.19 rt | any | >> OK Maybe X >> 2.6.24.19 rt | CPU0 | >> OK OK X >> 2.6.24.19 generic | any | >> X >> 2.6.24.19 generic | CPU0 | >> OK >> 2.6.29-rc3 vanilla-server | any | >> X >> 2.6.29-rc3 vanilla-server | CPU0 | >> OK >> 2.6.29-rc4 vanilla-generic | any | >> X OK >> 2.6.29-rc4 vanilla-generic | CPU0 | OK >> OK OK [5]_ OK >> -----------------------------------------+---------+----------+---------------+--------------+--------------+----------------- >> >> Broadcom >> BNX2 >> >> -----------------------------------------+---------+----------+---------------+--------------+--------------+----------------- >> >> 2.6.24-19 rt | MSI any | >> OK OK X >> 2.6.24-19 rt | MSI CPU0 | >> OK Maybe X >> 2.6.24-19 rt | APIC any | >> OK OK X >> 2.6.24-19 rt | APIC CPU0 | >> OK Maybe X >> 2.6.24-19-bnx-latest rt | APIC CPU0 | >> OK X >> 2.6.24-19 server | MSI any | >> X >> 2.6.24-19 server | MSI CPU0 | >> OK >> 2.6.24-19 generic | APIC any | >> X >> 2.6.24-19 generic | APIC CPU0 | >> OK >> 2.6.27-11 generic | APIC any | >> X >> 2.6.27-11 generic | APIC CPU0 | >> OK 10% drop >> 2.6.28-8 generic | APIC any | >> OK X >> 2.6.28-8 generic | APIC CPU0 | >> OK OK 0.5% drop >> 2.6.29-rc3 vanilla-server | MSI any | >> X >> 2.6.29-rc3 vanilla-server | MSI CPU0 | >> X >> 2.6.29-rc3 vanilla-server | APIC any | >> OK X >> 2.6.29-rc3 vanilla-server | APIC CPU0 | >> OK OK >> 2.6.29-rc4 vanilla-generic | APIC any | >> X >> 2.6.29-rc4 vanilla-generic | APIC CPU0 | >> OK 3% drop 10% drop X >> ====================== >> ==================+=========+==========+===============+==============+==============+================= >> >> * [4] MTools2 is a test from 29West: http://www.29west.com/docs/TestNet/ >> * [5] In 5 trials, 1 of the trials dropped 2%, 4 of the trials dropped >> nothing. >> >> Kenny >> > > Hi Kenny > > I am investigating how to reduce contention (and schedule() calls) on this workload. > I bound NIC (gigabit BNX2) irq to cpu 0, so that oprofile results on this cpu can show us where ksoftirqd is spending its time. We can see scheduler at work :) Also, one thing to note is __copy_skb_header() : 9.49 % of cpu0 time. The problem comes from dst_clone() (6.05 % total, so 2/3 of __copy_skb_header()), touching a highly contended cache line. (other cpus are doing the decrement of dst refcounter) CPU: Core 2, speed 3000.05 MHz (estimated) Counted CPU_CLK_UNHALTED events (Clock cycles when not halted) with a unit mask of 0x00 (Unhalted core cycles) count 100000 Samples on CPU 0 (samples for other cpus 1..7 omitted) samples cum. samples % cum. % symbol name 23750 23750 9.8159 9.8159 try_to_wake_up 22972 46722 9.4944 19.3103 __copy_skb_header 20217 66939 8.3557 27.6660 enqueue_task_fair 14565 81504 6.0197 33.6857 sock_def_readable 13454 94958 5.5606 39.2463 task_rq_lock 13381 108339 5.5304 44.7767 resched_task 13090 121429 5.4101 50.1868 udp_queue_rcv_skb 11441 132870 4.7286 54.9154 skb_queue_tail 10109 142979 4.1781 59.0935 sock_queue_rcv_skb 10024 153003 4.1429 63.2364 __wake_up_sync 9952 162955 4.1132 67.3496 update_curr 8761 171716 3.6209 70.9705 sched_clock_cpu 7414 179130 3.0642 74.0347 rb_insert_color 7381 186511 3.0506 77.0853 select_task_rq_fair 6749 193260 2.7894 79.8747 __slab_alloc 5881 199141 2.4306 82.3053 __wake_up_common 5432 204573 2.2451 84.5504 __skb_clone 4306 208879 1.7797 86.3300 kmem_cache_alloc 3524 212403 1.4565 87.7865 place_entity 2783 215186 1.1502 88.9367 skb_clone 2576 217762 1.0647 90.0014 __udp4_lib_rcv 2430 220192 1.0043 91.0057 bnx2_poll_work 2184 222376 0.9027 91.9084 ipt_do_table 2090 224466 0.8638 92.7722 ip_route_input 1877 226343 0.7758 93.5479 __alloc_skb 1495 227838 0.6179 94.1658 native_sched_clock 1166 229004 0.4819 94.6477 __update_sched_clock 1083 230087 0.4476 95.0953 netif_receive_skb 1062 231149 0.4389 95.5343 activate_task 644 231793 0.2662 95.8004 __kmalloc_track_caller 638 232431 0.2637 96.0641 nf_iterate 549 232980 0.2269 96.2910 skb_put -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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