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Message #177974
[Bug 1575407] Re: Trusty + 3.19 (lts-vivid) PERF wrong cpu-migration counter
It was brought to my attention traces from the buggy execution.
>From the perf statistics:
201054.649876 task-clock (msec) # 0.999 CPUs utilized
9,547 context-switches # 0.047 K/sec
6 cpu-migrations # 0.000 K/sec
6,427 page-faults # 0.032 K/sec
777,038,506,852 cycles # 3.865 GHz [66.66%]
1,799,766,809 stalled-cycles-frontend # 0.23% frontend cycles idle [50.00%]
518,104,985,732 stalled-cycles-backend # 66.68% backend cycles idle [50.01%]
819,194,804,419 instructions # 1.05 insns per cycle
# 0.63 stalled cycles per insn [66.67%]
90,811,473,192 branches # 451.676 M/sec [50.00%]
2,203,470,400 branch-misses # 2.43% of all branches [49.99%]
201.248973668 seconds time elapsed
**** We had 6 cpu-migrations.
>From tracing the execution we had exactly 6 set_task_cpus coming from
bottom halves (from the IRQ handler):
# coming from interrupt handler (1)
blackscholes-15443 [000] 5599.360541: function: set_task_cpu
blackscholes-15443 [000] 5599.360543: kernel_stack: <stack trace>
=> set_task_cpu (c0000000000eaa48)
=> try_to_wake_up (c0000000000ee998)
=> process_timeout (c00000000013f2e8)
=> call_timer_fn (c00000000013f154)
=> run_timer_softirq (c00000000013fd9c)
=> __do_softirq (c0000000000b5854)
=> irq_exit (c0000000000b5e28)
=> timer_interrupt (c00000000001fb94)
=> decrementer_common (c000000000002758)
# coming from interrupt handler (2)
blackscholes-15443 [000] 5600.800540: function: set_task_cpu
blackscholes-15443 [000] 5600.800542: kernel_stack: <stack trace>
=> set_task_cpu (c0000000000eaa48)
=> try_to_wake_up (c0000000000ee998)
=> commit_timeout (c0000000003d52f8)
=> call_timer_fn (c00000000013f154)
=> run_timer_softirq (c00000000013fd9c)
=> __do_softirq (c0000000000b5854)
=> irq_exit (c0000000000b5e28)
=> timer_interrupt (c00000000001fb94)
=> decrementer_common (c000000000002758)
# coming from interrupt handler (3)
blackscholes-15443 [000] 5603.840601: function: set_task_cpu
blackscholes-15443 [000] 5603.840603: kernel_stack: <stack trace>
=> set_task_cpu (c0000000000eaa48)
=> try_to_wake_up (c0000000000ee998)
=> hrtimer_wakeup (c000000000141a2c)
=> __run_hrtimer (c000000000141798)
=> hrtimer_interrupt (c0000000001427f8)
=> __timer_interrupt (c00000000001f480)
=> timer_interrupt (c00000000001fb90)
=> decrementer_common (c000000000002758)
# coming from interrupt handler (4)
blackscholes-15444 [000] 5629.340575: function: set_task_cpu
blackscholes-15444 [000] 5629.340577: kernel_stack: <stack trace>
=> set_task_cpu (c0000000000eaa48)
=> try_to_wake_up (c0000000000ee998)
=> wake_up_worker (c0000000000cf004)
=> __queue_work (c0000000000d1a0c)
=> queue_delayed_work_on (c0000000000d2244)
=> bnx2x_schedule_sp_task (d00000001bbe28cc)
=> bnx2x_msix_sp_int (d00000001bbfa200)
=> handle_irq_event_percpu (c0000000001287d0)
=> handle_irq_event (c000000000128ab8)
=> handle_fasteoi_irq (c00000000012cf74)
=> generic_handle_irq (c0000000001279c8)
=> __do_irq (c000000000010f60)
=> call_do_irq (c0000000000248ac)
=> do_IRQ (c000000000011150)
=> hardware_interrupt_common (c0000000000025d8)
# coming from interrupt handler (5)
blackscholes-15444 [000] 5636.625580: function: set_task_cpu
blackscholes-15444 [000] 5636.625582: kernel_stack: <stack trace>
=> set_task_cpu (c0000000000eaa48)
=> try_to_wake_up (c0000000000ee998)
=> hrtimer_wakeup (c000000000141a2c)
=> __run_hrtimer (c000000000141798)
=> hrtimer_interrupt (c0000000001427f8)
=> __timer_interrupt (c00000000001f480)
=> timer_interrupt (c00000000001fb90)
=> decrementer_common (c000000000002758)
# coming from interrupt handler (6)
blackscholes-15444 [000] 5640.856531: function: set_task_cpu
blackscholes-15444 [000] 5640.856533: kernel_stack: <stack trace>
=> set_task_cpu (c0000000000eaa48)
=> try_to_wake_up (c0000000000ee998)
=> process_timeout (c00000000013f2e8)
=> call_timer_fn (c00000000013f154)
=> run_timer_softirq (c00000000013fd9c)
=> __do_softirq (c0000000000b5854)
=> irq_exit (c0000000000b5e28)
=> timer_interrupt (c00000000001fb94)
=> decrementer_common (c000000000002758)
--
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https://bugs.launchpad.net/bugs/1575407
Title:
Trusty + 3.19 (lts-vivid) PERF wrong cpu-migration counter
Status in linux package in Ubuntu:
Confirmed
Bug description:
It was brought to my attention that:
In a PowerPC based server, PERF seems to acuse cpu-migrations when
only a single cpu is activated.
## perf
Performance counter stats for 'CPU(s) 0':
15027.888988 task-clock (msec) # 1.000 CPUs utilized [100.00%]
25,206 context-switches # 0.002 M/sec [100.00%]
3,518 cpu-migrations # 0.234 K/sec [100.00%]
639 page-faults # 0.043 K/sec
41,545,780,384 cycles # 2.765 GHz [66.68%]
2,868,753,319 stalled-cycles-frontend # 6.91% frontend cycles idle [50.01%]
30,162,193,535 stalled-cycles-backend # 72.60% backend cycles idle [50.01%]
11,161,722,533 instructions # 0.27 insns per cycle
# 2.70 stalled cycles per insn [66.68%]
1,544,072,679 branches # 102.747 M/sec [49.99%]
52,536,867 branch-misses # 3.40% of all branches [49.99%]
15.027768835 seconds time elapsed
## lscpu
Architecture: ppc64le
Byte Order: Little Endian
CPU(s): 128
On-line CPU(s) list: 0
Off-line CPU(s) list: 1-127
Thread(s) per core: 1
Core(s) per socket: 1
Socket(s): 1
NUMA node(s): 2
Model: 8335-GCA
L1d cache: 64K
L1i cache: 32K
L2 cache: 512K
L3 cache: 8192K
NUMA node0 CPU(s): 0
NUMA node8 CPU(s):
So either task migrations are being done to offline cpus or perf is
accounting it wrong.
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References
