* Re: Patch "rtla/timerlat: Make timerlat_top_cpu->*_count unsigned long long" has been added to the 6.6-stable tree
[not found] <20241210210407.3588978-1-sashal@kernel.org>
@ 2024-12-12 15:32 ` Tomas Glozar
2024-12-12 17:10 ` Greg KH
0 siblings, 1 reply; 2+ messages in thread
From: Tomas Glozar @ 2024-12-12 15:32 UTC (permalink / raw)
To: stable; +Cc: Steven Rostedt
út 10. 12. 2024 v 22:04 odesílatel Sasha Levin <sashal@kernel.org> napsal:
>
> This is a note to let you know that I've just added the patch titled
>
> rtla/timerlat: Make timerlat_top_cpu->*_count unsigned long long
>
> to the 6.6-stable tree which can be found at:
> http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
>
> The filename of the patch is:
> rtla-timerlat-make-timerlat_top_cpu-_count-unsigned-.patch
> and it can be found in the queue-6.6 subdirectory.
>
Could you also add "rtla/timerlat: Make timerlat_hist_cpu->*_count
unsigned long long", too (76b3102148135945b013797fac9b20), just like
we already have in-queue for 6.12? It makes no sense to do one fix but
not the other (clearly autosel AI won't take over the world yet).
> If you, or anyone else, feels it should not be added to the stable tree,
> please let <stable@vger.kernel.org> know about it.
>
>
>
> commit 0b8030ad5be8c39c4ad0f27fa740b3140a31023b
> Author: Tomas Glozar <tglozar@redhat.com>
> Date: Fri Oct 11 14:10:14 2024 +0200
>
> rtla/timerlat: Make timerlat_top_cpu->*_count unsigned long long
>
> [ Upstream commit 4eba4723c5254ba8251ecb7094a5078d5c300646 ]
>
> 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>
> Signed-off-by: Sasha Levin <sashal@kernel.org>
>
> diff --git a/tools/tracing/rtla/src/timerlat_top.c b/tools/tracing/rtla/src/timerlat_top.c
> index a84f43857de14..0915092057f85 100644
> --- a/tools/tracing/rtla/src/timerlat_top.c
> +++ b/tools/tracing/rtla/src/timerlat_top.c
> @@ -49,9 +49,9 @@ 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;
> @@ -237,7 +237,7 @@ 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);
>
Thanks,
Tomas
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