[Bug 1579278] Re: Keep powersave CPU frequency scaling governor for CPUs that support intel_pstate
Doug Smythies
1579278 at bugs.launchpad.net
Fri Sep 16 15:47:12 UTC 2016
>> The preferred governor with the intel_pstate driver is powersave.
> Do you have some references/proof for that? This is contrary to what
> kernel developers say, see comment 1.
In my opinion, that reference is obsolete.
While I don't work for Intel, the intel_pstate CPU frequency driver is
pretty much the only thing that I work on, and for a few years now, and
through 3 maintainers. Why would Intel expend so much effort on
powersave mode, if it were better to merely set performance mode and
forget about it? The objective with powersave mode is best energy/
performance tradeoff. There are still issues, yes. For example whenever
clock modulation becomes involved. Also, there can be a tendency to
incorrectly drive up the CPU frequency. There is work in progress that
should address these issues (see: http://askubuntu.com/questions/812530
/cpu-frequency-scaling-not-working-as-intended-on-vanilla-
ubuntu-16-04/812721#812721 and the reference links therein.)
I'll try to come back, maybe this weekend, with some energy comparison
numbers.
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https://bugs.launchpad.net/bugs/1579278
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:
Fix Released
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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