On Fri, 11 Oct 2024 14:10:14 +0200
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>
Thanks, I'm applying these, but could you or someone else create a test
directory in rtla and even rv that tests this code. I just examine it and
run some basic operations, but I have no idea if it is really working or not.
Having a utest directory or something would be really beneficial. That way,
I can at least run that test before I push it up to my tree.
-- Steve
