Re: [PATCH] printk: Print cpu number along with time

Andrew Morton
2014-09-10T21:26:30Z

On Tue, 9 Sep 2014 13:16:58 -0400 J__rn Engel <joern@logfs.org> wrote:

> On Wed, 4 June 2014 19:15:06 -0400, J__rn Engel wrote:
> > On Mon, 28 April 2014 17:22:19 -0700, Andrew Morton wrote:
> > > On Mon, 28 Apr 2014 19:40:39 -0400 J__rn Engel <joern@logfs.org> wrote:
> > > > On Thu, 24 April 2014 15:40:24 -0400, J__rn Engel wrote:
> > > > > On Wed, 23 April 2014 20:52:47 -0400, J__rn Engel wrote:
> > > > > >
> > > > > > I use the patch below for some time now. While it doesn't avoid the
> > > > > > log pollution in the first place, it lessens the impact somewhat.
> > > > >
> > > > > Added a config option and ported it to current -linus. Andrew, would
> > > > > you take this patch?
> > > >
> > > > Andrew? Did you dislike this patch for some reason or just miss it in
> > > > the thread?
> > >
> > > Neither ;) I try to respond in some way to all patches unless I think it's clear
> > > to the originator why I took no action. And I think I'm pretty good at
> > > not losing stuff.
> > >
> > > otoh, it has only been four days, three of which I spent offline...
> >
> > Ping.
>
> Ping.

It needs a resend please.

A few thoughts:

On Thu, 24 Apr 2014 15:40:24 -0400 J__rn Engel <joern@logfs.org> wrote:
>
> Sometimes the printk log is heavily interleaving between different cpus.
> This is particularly bad when you have two backtraces at the same time,
> but can be annoying in other cases as well. With an explicit cpu
> number, a simple grep can disentangle the mess for you.
>
> Signed-off-by: Joern Engel <joern@logfs.org>
> ---
> kernel/printk/printk.c | 19 ++++++++++++++++---
> lib/Kconfig.debug | 9 +++++++++
> 2 files changed, 25 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> index a45b50962295..b9e464924825 100644
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -200,6 +200,7 @@ struct printk_log {
> u16 len; /* length of entire record */
> u16 text_len; /* length of text buffer */
> u16 dict_len; /* length of dictionary buffer */
> + u16 cpu; /* cpu the message was generated on */
> u8 facility; /* syslog facility */
> u8 flags:5; /* internal record flags */
> u8 level:3; /* syslog level */
> @@ -346,6 +347,7 @@ static void log_store(int facility, int level,
> msg->facility = facility;
> msg->level = level & 7;
> msg->flags = flags & 0x1f;
> + msg->cpu = smp_processor_id();

Are you sure this won't generate smp_processor_id-in-preemptible
warnings? log_store has several callers..

> if (ts_nsec > 0)
> msg->ts_nsec = ts_nsec;
> else
> @@ -859,7 +861,7 @@ static bool printk_time;
> #endif
> module_param_named(time, printk_time, bool, S_IRUGO | S_IWUSR);
>
> -static size_t print_time(u64 ts, char *buf)
> +static size_t print_time(u64 ts, u16 cpu, char *buf)

The name is now wrong - it prints cpu number as well as time.

> {
> unsigned long rem_nsec;
>
> @@ -868,11 +870,20 @@ static size_t print_time(u64 ts, char *buf)
>
> rem_nsec = do_div(ts, 1000000000);
>
> +#ifdef CONFIG_PRINTK_CPU

This is regrettable. If someone wants the CPU number they have to
compile and install a new kernel? That's often impractical so we have
to hope that everyone enables the feature. And if they do that, why
did we need the Kconfigurability?

We have a printk.time boot parameter, so adding printk.cpu seems natural?

+ return snprintf(NULL, 0, "[%5lu.000000,%02x] ",

Printing hex numbers without 0x is just nasty. "11" = 17, surprise!