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

[Yash Shah]

Hi Andreas,

> -----Original Message-----
> From: Andreas Schwab <schwab at suse.de>
> Sent: 01 July 2020 16:11
> To: Yash Shah <yash.shah at sifive.com>
> Cc: Paul Walmsley ( Sifive) <paul.walmsley at sifive.com>;
> palmer at dabbelt.com; robh+dt at kernel.org; linux-riscv at lists.infradead.org;
> linux-kernel at vger.kernel.org; devicetree at vger.kernel.org; Sachin Ghadi
> <sachin.ghadi at sifive.com>; aou at eecs.berkeley.edu; anup at brainfault.org;
> lollivier at baylibre.com; Green Wan <green.wan at sifive.com>;
> atish.patra at wdc.com; alistair.francis at wdc.com; deepa.kernel at gmail.com;
> bmeng.cn at gmail.com
> Subject: Re: [PATCH 0/3] Dynamic CPU frequency switching for the HiFive
> 
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> 
> 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 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."

I am looking into the issues you reported. I will update soon.
Thanks for testing.

- Yash