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From:   Enlin Mu <enlinmu@gmail.com>
Date:   Fri, 15 Sep 2023 16:46:02 +0800
Message-ID: <CAAfh-jPc+UWMcLPFbYy6rYUh4OU36frkVYVbkhNPNX4L6RG5sA@mail.gmail.com>
Subject: Re: [PATCH] printk: add cpu id information to printk() output
To:     John Ogness <john.ogness@linutronix.de>
Cc:     Enlin Mu <enlin.mu@outlook.com>, pmladek@suse.com,
        rostedt@goodmis.org, senozhatsky@chromium.org,
        keescook@chromium.org, tony.luck@intel.com, gpiccoli@igalia.com,
        enlin.mu@unisoc.com, linux-kernel@vger.kernel.org,
        linux-hardening@vger.kernel.org
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John Ogness <john.ogness@linutronix.de> =E4=BA=8E2023=E5=B9=B49=E6=9C=8815=
=E6=97=A5=E5=91=A8=E4=BA=94 16:34=E5=86=99=E9=81=93=EF=BC=9A
>
> 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
>
> John Ogness

Thanks

Enlin