On Fri, 11 Oct 2024, tglo...@redhat.com wrote:
> From: Tomas Glozar <tglo...@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.
>
> Reported-by: Attila Fazekas <afaze...@redhat.com>
> Signed-off-by: Tomas Glozar <tglo...@redhat.com>
> ---
> 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 210b0f533534..ee7c291fc9bb 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);
> --
> 2.47.0
>
>
>
Reviewed by: John Kacur <jka...@redhat.com>
Tested by: John Kacur <jka...@redhat.com>
