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Message-ID: <1349271001.4465.66.camel@marge.simpson.net> Date: Wed, 03 Oct 2012 15:30:01 +0200 From: Mike Galbraith <efault@....de> To: Mel Gorman <mgorman@...e.de> Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>, Suresh Siddha <suresh.b.siddha@...el.com>, LKML <linux-kernel@...r.kernel.org> Subject: Re: Netperf UDP_STREAM regression due to not sending IPIs in ttwu_queue() On Wed, 2012-10-03 at 10:13 +0200, Mike Galbraith wrote: > Watching all cores instead. > > switch rate ~890KHz switch rate ~570KHz > NO_TTWU_QUEUE nohz=off TTWU_QUEUE nohz=off > 5.38% [kernel] [k] __schedule 4.81% [kernel] [k] _raw_spin_lock_irqsave > 4.29% [kernel] [k] _raw_spin_lock_irqsave 3.36% [kernel] [k] __skb_recv_datagram > 2.88% [kernel] [k] resched_task 2.71% [kernel] [k] copy_user_generic_string > 2.60% [kernel] [k] copy_user_generic_string 2.67% [kernel] [k] reschedule_interrupt > 2.38% [kernel] [k] __switch_to 2.62% [kernel] [k] sock_alloc_send_pskb > 2.15% [kernel] [k] sock_alloc_send_pskb 2.52% [kernel] [k] __schedule > 2.08% [kernel] [k] __skb_recv_datagram 2.31% [kernel] [k] try_to_wake_up > 1.81% [kernel] [k] udp_sendmsg 2.14% [kernel] [k] system_call > 1.76% [kernel] [k] system_call 1.98% [kernel] [k] udp_sendmsg > 1.73% [kernel] [k] __udp4_lib_lookup 1.96% [kernel] [k] __udp4_lib_lookup > 1.65% [kernel] [k] __slab_free.isra.42 1.78% [kernel] [k] sock_def_readable > 1.62% [kernel] [k] try_to_wake_up 1.63% [kernel] [k] __slab_free.isra.42 > 1.43% [kernel] [k] update_rq_clock 1.60% [kernel] [k] __switch_to > 1.43% [kernel] [k] sock_def_readable 1.52% [kernel] [k] dma_issue_pending_all > 1.41% [kernel] [k] dma_issue_pending_all 1.48% [kernel] [k] __ip_append_data.isra.35 > 1.40% [kernel] [k] menu_select 1.44% [kernel] [k] _raw_spin_lock > 1.36% [kernel] [k] finish_task_switch 1.38% [kernel] [k] _raw_spin_unlock_irqrestore > 1.30% [kernel] [k] ksize 1.33% [kernel] [k] __udp4_lib_rcv > > Strange. nohz=off, pipe-test with one half pinned to CPU0, the other to CPU1. procs -----------memory---------- ---swap-- -----io---- -system-- -----cpu------ r b swpd free buff cache si so bi bo in cs us sy id wa st TTW_QUEUE 1 0 0 3039488 50948 444720 0 0 0 0 539724 1013417 1 15 84 0 0 1 0 0 3039488 50956 444720 0 0 0 1 540853 1015679 1 15 84 0 0 1 0 0 3039364 50956 444720 0 0 0 0 541630 1017239 1 16 83 0 0 2 0 0 3038992 50956 444720 0 0 0 0 335550 1096569 4 20 76 0 0 NO_TTWU_QUEUE 1 0 0 3038992 50956 444720 0 0 0 0 33100 1318984 1 27 71 0 0 1 0 0 3038868 50956 444720 0 0 0 0 33100 1319126 2 27 71 0 0 1 0 0 3038868 50956 444720 0 0 0 0 33097 1317968 1 27 72 0 0 2 0 0 3038868 50964 444720 0 0 0 1 33104 1318558 2 27 71 0 0 We can switch faster with NO_TTWU_QUEUE, so we switch more, and that hurts netperf UDP_STREAM throughput.. somehow. Fatter is better is not the way context switch happy benchmarks usually work. -Mike -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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