[Bug 1579278] Re: Keep powersave CPU frequency scaling governor for CPUs that support intel_pstate

[Haw Loeung]

pitti, can we please have a config option to disable "ondemand"?

As originally reported, one some workloads, it seems setting to
powersave/ondemand causes high load with CPUs checking to see if they
need to enter powersave state.

While the original report included perf report for the acpi-cpufreq
driver, it was also seen with intel_pstate (and was why we decided to
try switch to acpi-cpufreq).

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Title:
  Keep powersave CPU frequency scaling governor for CPUs that support
  intel_pstate

Status in linux package in Ubuntu:
  Invalid
Status in systemd package in Ubuntu:
  In Progress
Status in sysvinit package in Ubuntu:
  Invalid
Status in linux source package in Xenial:
  Invalid
Status in systemd source package in Xenial:
  Invalid
Status in sysvinit source package in Xenial:
  Triaged

Bug description:
  Hi,

  With the new Ubuntu archive servers, we saw constantly high load and
  after some tinkering, we found that it was mostly CPUs being woken up
  to see if they should enter idle states. Changing the CPU frequency
  scaling governor to "performance" saw a considerable drop.

  Perf report using the following commands:

  | perf record -g -a sleep 10
  | perf report

  | Samples: 287K of event 'cycles:pp', Event count (approx.): 124776998906
  |   Children      Self  Command          Shared Object             Symbol
  | +   55.24%     0.20%  swapper          [kernel.kallsyms]         [k] cpu_startup_entry
  | +   53.51%     0.00%  swapper          [kernel.kallsyms]         [k] start_secondary
  | +   53.02%     0.08%  swapper          [kernel.kallsyms]         [k] call_cpuidle
  | +   52.94%     0.02%  swapper          [kernel.kallsyms]         [k] cpuidle_enter
  | +   31.81%     0.67%  swapper          [kernel.kallsyms]         [k] cpuidle_enter_state
  | +   29.59%     0.12%  swapper          [kernel.kallsyms]         [k] acpi_idle_enter
  | +   29.45%     0.05%  swapper          [kernel.kallsyms]         [k] acpi_idle_do_entry
  | +   29.43%    29.43%  swapper          [kernel.kallsyms]         [k] acpi_processor_ffh_cstate_enter
  | +   20.51%     0.04%  swapper          [kernel.kallsyms]         [k] ret_from_intr
  | +   20.47%     0.12%  swapper          [kernel.kallsyms]         [k] do_IRQ
  | +   19.30%     0.07%  swapper          [kernel.kallsyms]         [k] irq_exit
  | +   19.18%     0.07%  apache2          [kernel.kallsyms]         [k] entry_SYSCALL_64_fastpath
  | +   18.80%     0.17%  swapper          [kernel.kallsyms]         [k] __do_softirq
  | +   16.45%     0.11%  swapper          [kernel.kallsyms]         [k] net_rx_action
  | +   16.25%     0.43%  swapper          [kernel.kallsyms]         [k] be_poll
  | +   14.74%     0.21%  swapper          [kernel.kallsyms]         [k] be_process_rx
  | +   13.61%     0.07%  swapper          [kernel.kallsyms]         [k] napi_gro_frags
  | +   12.58%     0.04%  swapper          [kernel.kallsyms]         [k] netif_receive_skb_internal
  | +   12.48%     0.03%  swapper          [kernel.kallsyms]         [k] __netif_receive_skb
  | +   12.42%     0.24%  swapper          [kernel.kallsyms]         [k] __netif_receive_skb_core
  | +   12.41%     0.00%  apache2          [unknown]                 [k] 0x00007f27983b5028
  | +   12.41%     0.00%  apache2          [unknown]                 [k] 0x00007f2798369028
  | +   11.49%     0.16%  swapper          [kernel.kallsyms]         [k] ip_rcv
  | +   11.29%     0.09%  swapper          [kernel.kallsyms]         [k] ip_rcv_finish
  | +   10.77%     0.05%  swapper          [kernel.kallsyms]         [k] ip_local_deliver
  | +   10.70%     0.06%  swapper          [kernel.kallsyms]         [k] ip_local_deliver_finish
  | +   10.55%     0.22%  swapper          [kernel.kallsyms]         [k] tcp_v4_rcv
  | +   10.10%     0.00%  apache2          [unknown]                 [k] 0000000000000000
  | +   10.01%     0.04%  swapper          [kernel.kallsyms]         [k] tcp_v4_do_rcv

  Expanding in a few of those, you'll see:

  | -   55.24%     0.20%  swapper          [kernel.kallsyms]         [k] cpu_startup_entry
  |    - 55.04% cpu_startup_entry
  |       - 52.98% call_cpuidle
  |          + 52.93% cpuidle_enter
  |          + 0.00% ret_from_intr
  |            0.00% cpuidle_enter_state
  |            0.00% irq_entries_start
  |       + 1.14% cpuidle_select
  |       + 0.47% schedule_preempt_disabled
  |         0.10% rcu_idle_enter
  |         0.09% rcu_idle_exit
  |       + 0.05% ret_from_intr
  |       + 0.05% tick_nohz_idle_enter
  |       + 0.04% arch_cpu_idle_enter
  |         0.02% cpuidle_enter
  |         0.02% tick_check_broadcast_expired
  |       + 0.01% cpuidle_reflect
  |         0.01% menu_reflect
  |         0.01% atomic_notifier_call_chain
  |         0.01% local_touch_nmi
  |         0.01% cpuidle_not_available
  |         0.01% menu_select
  |         0.01% cpuidle_get_cpu_driver
  |       + 0.01% tick_nohz_idle_exit
  |       + 0.01% sched_ttwu_pending
  |         0.00% set_cpu_sd_state_idle
  |         0.00% native_irq_return_iret
  |         0.00% schedule
  |       + 0.00% arch_cpu_idle_exit
  |         0.00% __tick_nohz_idle_enter
  |         0.00% irq_entries_start
  |         0.00% sched_clock_idle_wakeup_event
  |         0.00% reschedule_interrupt
  |       + 0.00% apic_timer_interrupt
  |    + 0.20% start_secondary
  |    + 0.00% x86_64_start_kernel
  | +   53.51%     0.00%  swapper          [kernel.kallsyms]         [k] start_secondary
  | +   53.02%     0.08%  swapper          [kernel.kallsyms]         [k] call_cpuidle
  | -   52.94%     0.02%  swapper          [kernel.kallsyms]         [k] cpuidle_enter
  |    - 52.92% cpuidle_enter
  |       + 31.81% cpuidle_enter_state
  |       + 20.01% ret_from_intr
  |       + 0.51% apic_timer_interrupt
  |         0.28% native_irq_return_iret
  |       + 0.09% reschedule_interrupt
  |         0.05% irq_entries_start
  |         0.05% do_IRQ
  |         0.05% common_interrupt
  |         0.02% sched_idle_set_state
  |         0.01% acpi_idle_enter
  |         0.01% ktime_get
  |         0.01% restore_regs_and_iret
  |         0.01% restore_c_regs_and_iret
  |       + 0.01% call_function_single_interrupt
  |         0.00% native_iret
  |       + 0.00% call_function_interrupt
  |         0.00% smp_apic_timer_interrupt
  |         0.00% smp_reschedule_interrupt
  |         0.00% smp_call_function_single_interrupt
  |    + 0.02% start_secondary

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