Re: [PATCH] printk: add cpu id information to printk() output

[John Ogness]

On 2023-09-15, Enlin Mu <enlin.mu@xxxxxxxxxxx> wrote:
> Sometimes we want to print cpu id of printk() messages to consoles
>
> diff --git a/include/linux/threads.h b/include/linux/threads.h
> index c34173e6c5f1..6700bd9a174f 100644
> --- a/include/linux/threads.h
> +++ b/include/linux/threads.h
> @@ -34,6 +34,9 @@
>  #define PID_MAX_LIMIT (CONFIG_BASE_SMALL ? PAGE_SIZE * 8 : \
>  	(sizeof(long) > 4 ? 4 * 1024 * 1024 : PID_MAX_DEFAULT))
>  
> +#define CPU_ID_SHIFT 23
> +#define CPU_ID_MASK  0xff800000

This only supports 256 CPUs. I think it doesn't make sense to try to
squish CPU and Task IDs into 32 bits.

What about introducing a caller_id option to always only print the CPU
ID? Or do you really need Task _and_ CPU?

John Ogness