Re: [RFC] panic: reduce CPU consumption when finished handling panic

[Carlos Bilbao]

+CCed Jan Glauber as he'd figure as Co-developed-by if this goes through.

Thanks,

Carlos


On 3/17/25 17:01, Carlos Bilbao wrote:
> After the kernel has finished handling a panic, it enters a busy-wait loop.
> But, this unnecessarily consumes CPU power and electricity. Plus, in VMs,
> this negatively impacts the throughput of other VM guests running on the
> same hypervisor.
>
> I propose introducing a function cpu_halt_end_panic() to halt the CPU
> during this state while still allowing interrupts to be processed. See my
> commit below.
>
> Thanks in advance!
>
> Signed-off-by: Carlos Bilbao <carlos.bilbao@xxxxxxxxxx>
> ---
>  kernel/panic.c | 17 ++++++++++++++++-
>  1 file changed, 16 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/panic.c b/kernel/panic.c
> index fbc59b3b64d0..c00ccaa698d5 100644
> --- a/kernel/panic.c
> +++ b/kernel/panic.c
> @@ -276,6 +276,21 @@ static void panic_other_cpus_shutdown(bool crash_kexec)
>          crash_smp_send_stop();
>  }
>  
> +static void cpu_halt_end_panic(void)
> +{
> +#ifdef CONFIG_X86
> +    native_safe_halt();
> +#elif defined(CONFIG_ARM)
> +    cpu_do_idle();
> +#else
> +    /*
> +     * Default to a simple busy-wait if no architecture-specific halt is
> +     * defined above
> +     */
> +    mdelay(PANIC_TIMER_STEP);
> +#endif
> +}
> +
>  /**
>   *    panic - halt the system
>   *    @fmt: The text string to print
> @@ -474,7 +489,7 @@ void panic(const char *fmt, ...)
>              i += panic_blink(state ^= 1);
>              i_next = i + 3600 / PANIC_BLINK_SPD;
>          }
> -        mdelay(PANIC_TIMER_STEP);
> +        cpu_halt_end_panic();
>      }
>  }
>