[for-next][PATCH 8/9] rtla/timerlat: Make timerlat_top_cpu->*_count unsigned long long

Steven Rostedt
2024-10-11T17:30:18Z

From: Tomas Glozar <tglozar@redhat.com>

Most fields of struct timerlat_top_cpu are unsigned long long, but the
fields {irq,thread,user}_count are int (32-bit signed).

This leads to overflow when tracing on a large number of CPUs for a long
enough time:
$ rtla timerlat top -a20 -c 1-127 -d 12h
...
0 12:00:00 | IRQ Timer Latency (us) | Thread Timer Latency (us)
CPU COUNT | cur min avg max | cur min avg max
1 #43200096 | 0 0 1 2 | 3 2 6 12
...
127 #43200096 | 0 0 1 2 | 3 2 5 11
ALL #119144 e4 | 0 5 4 | 2 28 16

The average latency should be 0-1 for IRQ and 5-6 for thread, but is
reported as 5 and 28, about 4 to 5 times more, due to the count
overflowing when summed over all CPUs: 43200096 * 127 = 5486412192,
however, 1191444898 (= 5486412192 mod MAX_INT) is reported instead, as
seen on the last line of the output, and the averages are thus ~4.6
times higher than they should be (5486412192 / 1191444898 = ~4.6).

Fix the issue by changing {irq,thread,user}_count fields to unsigned
long long, similarly to other fields in struct timerlat_top_cpu and to
the count variable in timerlat_top_print_sum.

Link: https://lore.kernel.org/20241011121015.2868751-1-tglozar@redhat.com
Reported-by: Attila Fazekas <afazekas@redhat.com>
Signed-off-by: Tomas Glozar <tglozar@redhat.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
tools/tracing/rtla/src/timerlat_top.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/tools/tracing/rtla/src/timerlat_top.c b/tools/tracing/rtla/src/timerlat_top.c
index 94a2f5bbaeb7..7fb85c8ee3bc 100644
--- a/tools/tracing/rtla/src/timerlat_top.c
+++ b/tools/tracing/rtla/src/timerlat_top.c
@@ -54,9 +54,9 @@ struct timerlat_top_params {
};

struct timerlat_top_cpu {
- int irq_count;
- int thread_count;
- int user_count;
+ unsigned long long irq_count;
+ unsigned long long thread_count;
+ unsigned long long user_count;

unsigned long long cur_irq;
unsigned long long min_irq;
@@ -280,7 +280,7 @@ static void timerlat_top_print(struct osnoise_tool *top, int cpu)
/*
* Unless trace is being lost, IRQ counter is always the max.
*/
- trace_seq_printf(s, "%3d #%-9d |", cpu, cpu_data->irq_count);
+ trace_seq_printf(s, "%3d #%-9llu |", cpu, cpu_data->irq_count);

if (!cpu_data->irq_count) {
trace_seq_printf(s, "%s %s %s %s |", no_value, no_value, no_value, no_value);
--
2.45.2