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Date: Mon, 20 Jan 2014 09:19:40 -0800
From: Eric Dumazet <eric.dumazet@...il.com>
To: Fengguang Wu <fengguang.wu@...el.com>
Cc: Eric Dumazet <edumazet@...gle.com>,
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: [rcu] 878d7439d0: -100% softirqs.RCU
On Mon, 2014-01-20 at 17:30 +0800, Fengguang Wu wrote:
> Hi Eric,
>
> Just FYI, we noticed the below changes in old commit 878d7439d0 ("rcu:
> Fix batch-limit size problem") in test case will-it-scale/open1:
>
> 62da1921292ef78 878d7439d0f45a95869e41757
> --------------- -------------------------
> 0.00 ~200% +60900.0% 1.22 ~18% TOTAL perf-profile.cpu-clock.file_free_rcu.rcu_process_callbacks.__do_softirq.call_softirq.do_softirq
> 0.28 ~126% +339.3% 1.23 TOTAL perf-profile.cpu-clock.__d_lookup_rcu.link_path_walk.do_filp_open.do_sys_open.sys_open
> 1.16 ~15% -100.0% 0.00 TOTAL perf-profile.cpu-clock.file_free_rcu.rcu_process_callbacks.__do_softirq.run_ksoftirqd.smpboot_thread_fn
> 1.89e+08 ~14% -100.0% 63093 ~ 6% TOTAL softirqs.RCU
> 3.66 ~ 7% -100.0% 0.00 TOTAL perf-profile.cpu-clock.rcu_process_callbacks.__do_softirq.run_ksoftirqd.smpboot_thread_fn.kthread
> 1.29 ~11% -100.0% 0.00 TOTAL perf-profile.cpu-clock.rcu_process_gp_end.isra.23.rcu_process_callbacks.__do_softirq.run_ksoftirqd.smpboot_thread_fn
> 1.39 ~ 9% -100.0% 0.00 TOTAL perf-profile.cpu-clock.check_for_new_grace_period.isra.25.rcu_process_callbacks.__do_softirq.run_ksoftirqd.smpboot_thread_fn
> 57276 ~ 9% +110.2% 120367 ~15% TOTAL slabinfo.kmalloc-256.active_objs
> 3582 ~ 9% +110.0% 7525 ~15% TOTAL slabinfo.kmalloc-256.active_slabs
> 3582 ~ 9% +110.0% 7525 ~15% TOTAL slabinfo.kmalloc-256.num_slabs
> 57331 ~ 9% +110.0% 120407 ~15% TOTAL slabinfo.kmalloc-256.num_objs
> 23741 ~ 6% +71.2% 40652 ~13% TOTAL meminfo.SUnreclaim
> 19830 ~ 4% -44.1% 11094 ~ 8% TOTAL interrupts.RES
> 6113 ~ 8% +74.6% 10674 ~12% TOTAL proc-vmstat.nr_slab_unreclaimable
> 2.44 ~13% +62.9% 3.98 ~13% TOTAL perf-profile.cpu-clock.__slab_alloc.kmem_cache_alloc.get_empty_filp.do_filp_open.do_sys_open
> 3 ~ 0% -33.3% 2 ~ 0% TOTAL vmstat.procs.r
> 53183 ~ 3% +31.6% 70006 ~ 8% TOTAL meminfo.Slab
> 1001 ~ 9% -14.3% 858 ~10% TOTAL slabinfo.kmalloc-128.num_objs
> 1001 ~ 9% -14.3% 858 ~10% TOTAL slabinfo.kmalloc-128.active_objs
> 2.47 ~ 7% +12.1% 2.76 ~ 6% TOTAL perf-profile.cpu-clock.__call_rcu.call_rcu_sched.__fput.____fput.task_work_run
> 6686 ~ 5% -95.9% 272 ~ 3% TOTAL time.involuntary_context_switches
> 109 ~ 1% +21.3% 132 ~ 1% TOTAL time.system_time
> 55 ~ 0% +19.6% 66 ~ 0% TOTAL time.percent_of_cpu_this_job_got
> 899 ~ 3% +10.5% 993 ~ 7% TOTAL vmstat.system.cs
>
> time.system_time
>
> 140 ++-------------------------------------------------------------------+
> | O O O O |
> 135 ++ |
> O O O O O O O O O O O O O O O O O O O O O
> 130 ++ O O O O O O O O O |
> | |
> 125 ++ |
> | |
> 120 ++ |
> | |
> 115 ++ |
> | .*. .*. *.. |
> 110 *+ .*. .*. .*.*.*. .* *.*.*..*.*.*.* *. .*. + .*. |
> | * *.*.*. * * * *.* *.* * |
> 105 ++-------------------------------------------------------------------+
>
>
> time.percent_of_cpu_this_job_got
>
> 66 O+O-O-O-O--O-O-O-O-O-O-O-O--O-O-O-O-O-O-O-O--O-O-O-O-O-O-O-O--O-O-O-O-O
> | |
> 64 ++ |
> | |
> | |
> 62 ++ |
> | |
> 60 ++ |
> | |
> 58 ++ |
> | * * |
> | + + + + |
> 56 ++ .*.*. + *.*.*.*.* *..*.*. .*. |
> *.*.*.*.*..*.*.*.* *.* *.*.*.* *..*.*.* |
> 54 ++--------------------------------------------------------------------+
>
>
> time.involuntary_context_switches
>
> 9000 ++------------------------------------------------------------------+
> | * |
> 8000 ++ .*.*. .* * *. .*.*. .* *. + + .*. |
> 7000 *+* * + + + .. * *.*.*.*.* + + *.* *. *. .*.*. |
> | * * * * *.* |
> 6000 ++ |
> 5000 ++ |
> | |
> 4000 ++ |
> 3000 ++ |
> | |
> 2000 ++ |
> 1000 ++ |
> | O O O |
> 0 O+--O-O---O---O-O--O-O-O-O-O-O-O-O-O-O-O-O-O-O-O-O--O-O-O-O-O-O-O-O-O
I had to track the bug because at that time, IP route cache was not yet
removed, and a moderate workload was able to hit
proc/sys/net/ipv4/route/gc_thresh very fast, for no good reasons.
So I am not surprised that you can reproduce the issue with a synthetic
test ;)
Thanks !
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