Re: [sched] WARNING: CPU: 0 PID: 0 at arch/x86/kernel/cpu/common.c:1439 warn_pre_alternatives()

[Dietmar Eggemann]

Hi Fengguang,

On 11/12/14 00:26, Fengguang Wu wrote:
> Hi Dietmar,
>
> FYI, here is another bisect result.

thanks for testing this on another arch then ARM!

The problem is that the weak arch_scale_cpu_capacity calls 
default_scale_cpu_capacity on a system which doesn't overwrite it and 
the default one accesses the sched_domain which is not allocated that 
early when called by scheduler_tick.

I only tested it on an ARM system which in this tree which overwrites 
arch_scale_cpu_capacity and does not access sched_domain.

Have to look into it and will test the default case from now on too.

-- Dietmar

> https://git.linaro.org/people/mturquette/linux.git eas-next
> commit 1fadb581b0be9420b143e43ff2f4a07ea7e45f6c
> Author:     Dietmar Eggemann <dietmar.eggemann@xxxxxxx>
> AuthorDate: Tue Dec 2 14:06:24 2014 +0000
> Commit:     Michael Turquette <mturquette@xxxxxxxxxxx>
> CommitDate: Tue Dec 9 20:33:17 2014 -0800
>
>      sched: Make usage and load tracking cpu scale-invariant
>
>      Besides the existing frequency scale-invariance correction factor, apply
>      cpu scale-invariance correction factor to usage and load tracking.
>
>      Cpu scale-invariance takes cpu performance deviations due to
>      micro-architectural differences (i.e. instructions per seconds) between
>      cpus in HMP systems (e.g. big.LITTLE) and differences in the frequency
>      value of the highest OPP between cpus in SMP systems into consideration.
>
>      Each segment of the sched_avg::{running_avg_sum, runnable_avg_sum}
>      geometric series is now scaled by the cpu performance factor too so the
>      sched_avg::{utilization_avg_contrib, load_avg_contrib} of each entity will
>      be invariant from the particular cpu of the HMP/SMP system it is gathered
>      on. As a result, cfs_rq::runnable_load_avg which is the sum of
>      sched_avg::load_avg_contrib, becomes cpu scale-invariant too.
>
>      So the {usage, load} level that is returned by {get_cpu_usage,
>      weighted_cpuload} stays relative to the max cpu performance of the system.
>
>      Cc: Ingo Molnar <mingo@xxxxxxxxxx>
>      Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
>      Signed-off-by: Dietmar Eggemann <dietmar.eggemann@xxxxxxx>

[...]


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