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Subject[PATCH] output the cpu number when printking.
From
Date
From: "he, bo" <bo.he@intel.com>

We often hit kernel panic issues on SMP machines because processes race
on multiple cpu. By adding a new parameter printk.cpu, kernel prints
cpu number at printk information line. It’s useful to debug what cpus
are racing.

Signed-off-by: he, bo <bo.he@intel.com>
---
Documentation/kernel-parameters.txt | 4 ++++
kernel/printk.c | 18 ++++++++++++++++--
2 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index ddd84d6..ccd5266 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -2378,6 +2378,10 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
printk.time= Show timing data prefixed to each printk message line
Format: <bool> (1/Y/y=enable, 0/N/n=disable)

+ printk.cpu= Show cpu data prefixed to each printk message line
+ Format: <bool> (1/Y/y=enable, 0/N/n=disable)
+ printk.cpu takes effect only when printk.time=y.
+
processor.max_cstate= [HW,ACPI]
Limit processor to maximum C-state
max_cstate=9 overrides any DMI blacklist limit.
diff --git a/kernel/printk.c b/kernel/printk.c
index 19c0d7b..873a226 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -863,9 +863,14 @@ static bool printk_time;
#endif
module_param_named(time, printk_time, bool, S_IRUGO | S_IWUSR);

+static bool printk_cpu = 1;
+module_param_named(cpu, printk_cpu, bool, S_IRUGO | S_IWUSR);
+
static size_t print_time(u64 ts, char *buf)
{
unsigned long rem_nsec;
+ size_t len = 0;
+ int this_cpu;

if (!printk_time)
return 0;
@@ -874,8 +879,17 @@ static size_t print_time(u64 ts, char *buf)
return 15;

rem_nsec = do_div(ts, 1000000000);
- return sprintf(buf, "[%5lu.%06lu] ",
- (unsigned long)ts, rem_nsec / 1000);
+
+ if (printk_cpu) {
+ this_cpu = raw_smp_processor_id();
+ len = sprintf(buf, "[%5lu.%06lu,%u] ",
+ (unsigned long)ts, rem_nsec / 1000, this_cpu);
+ } else {
+ len = sprintf(buf, "[%5lu.%06lu] ",
+ (unsigned long)ts, rem_nsec / 1000);
+ }
+
+ return len;
}

static size_t print_prefix(const struct log *msg, bool syslog, char *buf)
--
1.7.6


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