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

Jörn Engel
2014-04-28T23:41:39Z

On Thu, 24 April 2014 15:40:24 -0400, Jörn Engel wrote:
> On Wed, 23 April 2014 20:52:47 -0400, Jörn 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?

> ---
>
> 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();
> 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)
> {
> 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
> + if (!buf)
> + return snprintf(NULL, 0, "[%5lu.000000,%02x] ",
> + (unsigned long)ts, cpu);
> +
> + return sprintf(buf, "[%5lu.%06lu,%02x] ",
> + (unsigned long)ts, rem_nsec / 1000, cpu);
> +#else
> if (!buf)
> return snprintf(NULL, 0, "[%5lu.000000] ", (unsigned long)ts);
>
> return sprintf(buf, "[%5lu.%06lu] ",
> (unsigned long)ts, rem_nsec / 1000);
> +#endif
> }
>
> static size_t print_prefix(const struct printk_log *msg, bool syslog, char *buf)
> @@ -894,7 +905,7 @@ static size_t print_prefix(const struct printk_log *msg, bool syslog, char *buf)
> }
> }
>
> - len += print_time(msg->ts_nsec, buf ? buf + len : NULL);
> + len += print_time(msg->ts_nsec, msg->cpu, buf ? buf + len : NULL);
> return len;
> }
>
> @@ -1391,6 +1402,7 @@ static struct cont {
> size_t cons; /* bytes written to console */
> struct task_struct *owner; /* task of first print*/
> u64 ts_nsec; /* time of first print */
> + u16 cpu; /* cpu the message was generated on */
> u8 level; /* log level of first message */
> u8 facility; /* log level of first message */
> enum log_flags flags; /* prefix, newline flags */
> @@ -1440,6 +1452,7 @@ static bool cont_add(int facility, int level, const char *text, size_t len)
> cont.facility = facility;
> cont.level = level;
> cont.owner = current;
> + cont.cpu = smp_processor_id();
> cont.ts_nsec = local_clock();
> cont.flags = 0;
> cont.cons = 0;
> @@ -1461,7 +1474,7 @@ static size_t cont_print_text(char *text, size_t size)
> size_t len;
>
> if (cont.cons == 0 && (console_prev & LOG_NEWLINE)) {
> - textlen += print_time(cont.ts_nsec, text);
> + textlen += print_time(cont.ts_nsec, cont.cpu, text);
> size -= textlen;
> }
>
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index 819ac51202c0..bdec67eca521 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -15,6 +15,15 @@ config PRINTK_TIME
> The behavior is also controlled by the kernel command line
> parameter printk.time=1. See Documentation/kernel-parameters.txt
>
> +config PRINTK_CPU
> + bool "Show CPU number along with timing information"
> + depends on PRINTK_TIME
> + help
> + Selecting this option adds the CPU number to be added to
> + timestamps of printk() messages. This can be useful when
> + messages from several CPUs are interleaved, in particular
> + for stack traces.
> +
> config DEFAULT_MESSAGE_LOGLEVEL
> int "Default message log level (1-7)"
> range 1 7
> --
> 2.0.0.rc0.1.g7b2ba98
>

Jörn

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