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trace/hwlat: Remove printk from sampling loop

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hwlat has some time operation checks on the sample loop, and it is
currently using pr_err (printk) to report them. The problem is that
this can lead the system to an unresponsible state due to an overflow of
printk messages. This problem can be mitigated by writing the error
message to the trace buffer.

Remove the printk messages from the sampling loop, switching the to
messages in the trace buffer.

No functional change.

Link: https://lkml.kernel.org/r/9d77c34869748aa105e965c769d24642914eea3a.1624372313.git.bristot@redhat.com

Cc: Phil Auld <pauld@redhat.com>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Kate Carcia <kcarcia@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Alexandre Chartre <alexandre.chartre@oracle.com>
Cc: Clark Willaims <williams@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: x86@kernel.org
Cc: linux-doc@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Daniel Bristot de Oliveira <bristot@redhat.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
This commit is contained in:
Daniel Bristot de Oliveira 2021-06-22 16:42:25 +02:00 committed by Steven Rostedt (VMware)
parent f27a1c9e1b
commit aa892f8c88
1 changed files with 12 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

15
kernel/trace/trace_hwlat.c
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@ -182,6 +182,15 @@ void trace_hwlat_callback(bool enter)
kdata->nmi_count++; kdata->nmi_count++;
} }
/*
* hwlat_err - report a hwlat error.
*/
#define hwlat_err(msg) ({ \
struct trace_array *tr = hwlat_trace; \
\
trace_array_printk_buf(tr->array_buffer.buffer, _THIS_IP_, msg); \
})
/** /**
* get_sample - sample the CPU TSC and look for likely hardware latencies * get_sample - sample the CPU TSC and look for likely hardware latencies
* *
@ -225,7 +234,7 @@ static int get_sample(void)
outer_diff = time_to_us(time_sub(t1, last_t2)); outer_diff = time_to_us(time_sub(t1, last_t2));
/* This shouldn't happen */ /* This shouldn't happen */
if (outer_diff < 0) { if (outer_diff < 0) {
pr_err(BANNER "time running backwards\n"); hwlat_err(BANNER "time running backwards\n");
goto out; goto out;
} }
if (outer_diff > outer_sample) if (outer_diff > outer_sample)
@ -237,7 +246,7 @@ static int get_sample(void)
/* Check for possible overflows */ /* Check for possible overflows */
if (total < last_total) { if (total < last_total) {
pr_err("Time total overflowed\n"); hwlat_err("Time total overflowed\n");
break; break;
} }
last_total = total; last_total = total;
@ -253,7 +262,7 @@ static int get_sample(void)
/* This shouldn't happen */ /* This shouldn't happen */
if (diff < 0) { if (diff < 0) {
pr_err(BANNER "time running backwards\n"); hwlat_err(BANNER "time running backwards\n");
goto out; goto out;
} }