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

[Greg KH <gregkh@linuxfoundation.org>]

On Fri, Sep 15, 2023 at 04:46:02PM +0800, Enlin Mu wrote:
> John Ogness <john.ogness@linutronix.de> 于2023年9月15日周五 16:34写道：
> >
> > On 2023-09-15, Enlin Mu <enlin.mu@outlook.com> 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.
> Yes, it is not good way,
> >
> > What about introducing a caller_id option to always only print the CPU
> > ID? Or do you really need Task _and_ CPU?
>    Yes, I need it.Because I need to know which CPU is printing the
> log, so that I can identify the current system operation, such as load
> situation and CPU busy/idle status

The cpu that is printing the log isn't the one that added the log
message, so I think you will have incorrect data here, right?

thanks,

greg k-h