[PATCH 0/3] Dynamic CPU frequency switching for the HiFive

[David Abdurachmanov]

On Wed, Jul 1, 2020 at 1:41 PM Andreas Schwab <schwab at suse.de> wrote:
>
> On Jun 16 2020, Yash Shah wrote:
>
> > The patch series adds the support for dynamic CPU frequency switching
> > for FU540-C000 SoC on the HiFive Unleashed board. All the patches are
> > based on Paul Walmsley's work.
> >
> > This series is based on Linux v5.7 and tested on HiFive unleashed board.
>
> I'm using that patch with 5.7.5.
>
> It appears to interfer with serial output when using the ondemand
> governor.

I do recall that userspace governor is the only one supported but this
might have changed before this patch was posted.

Yash, do you have more details?

>
> I also see soft lockups when using the performance governor:
>
> [  101.587527] rcu: INFO: rcu_sched self-detected stall on CPU
> [  101.592322] rcu:     0-...!: (932 ticks this GP) idle=11a/1/0x4000000000000004 softirq=4301/4301 fqs=4
> [  101.601432]  (t=6001 jiffies g=4017 q=859)
> [  101.605514] rcu: rcu_sched kthread starved for 5984 jiffies! g4017 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=2
> [  101.615494] rcu: RCU grace-period kthread stack dump:
> [  101.620530] rcu_sched       R  running task        0    10      2 0x00000000
> [  101.627560] Call Trace:
> [  101.630004] [<ffffffe00085a7e2>] __schedule+0x25c/0x616
> [  101.635205] [<ffffffe00085abde>] schedule+0x42/0xb2
> [  101.640070] [<ffffffe00085d0ba>] schedule_timeout+0x56/0xb8
> [  101.645626] [<ffffffe000263c34>] rcu_gp_fqs_loop+0x208/0x248
> [  101.651266] [<ffffffe0002666de>] rcu_gp_kthread+0xc2/0xcc
> [  101.656651] [<ffffffe00022654e>] kthread+0xda/0xec
> [  101.661426] [<ffffffe00020140a>] ret_from_exception+0x0/0xc
> [  101.666977] Task dump for CPU 0:
> [  101.670187] loop0           R  running task        0   655      2 0x00000008
> [  101.677218] Call Trace:
> [  101.679657] [<ffffffe0002028ae>] walk_stackframe+0x0/0xaa
> [  101.685036] [<ffffffe000202b76>] show_stack+0x2a/0x34
> [  101.690074] [<ffffffe0002319b0>] sched_show_task.part.0+0xc2/0xd2
> [  101.696154] [<ffffffe00022bb9c>] sched_show_task+0x64/0x66
> [  101.701618] [<ffffffe000231afe>] dump_cpu_task+0x3e/0x48
> [  101.706916] [<ffffffe000267762>] rcu_dump_cpu_stacks+0x94/0xce
> [  101.712731] [<ffffffe0002631f6>] print_cpu_stall+0x116/0x18a
> [  101.718375] [<ffffffe000264a46>] check_cpu_stall+0xcc/0x1a2
> [  101.723929] [<ffffffe000264b52>] rcu_pending.constprop.0+0x36/0xaa
> [  101.730094] [<ffffffe000266ab2>] rcu_sched_clock_irq+0xa6/0xea
> [  101.735913] [<ffffffe00026d1be>] update_process_times+0x1e/0x42
> [  101.741821] [<ffffffe0002793bc>] tick_sched_handle+0x26/0x52
> [  101.747456] [<ffffffe0002798fe>] tick_sched_timer+0x6a/0xd0
> [  101.753015] [<ffffffe00026d9be>] __run_hrtimer.constprop.0+0x50/0xe8
> [  101.759353] [<ffffffe00026da9e>] __hrtimer_run_queues+0x48/0x6c
> [  101.765254] [<ffffffe00026e410>] hrtimer_interrupt+0xca/0x1d4
> [  101.770985] [<ffffffe0006ceef8>] riscv_timer_interrupt+0x32/0x3a
> [  101.776976] [<ffffffe00085e17c>] do_IRQ+0xa4/0xb8
> [  101.781663] [<ffffffe00020140a>] ret_from_exception+0x0/0xc
>
> Andreas.
>
> --
> Andreas Schwab, SUSE Labs, schwab at suse.de
> GPG Key fingerprint = 0196 BAD8 1CE9 1970 F4BE  1748 E4D4 88E3 0EEA B9D7
> "And now for something completely different."
>
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