Tomas Glozar
77c9ad0c42
[ Upstream commit 4eba4723c5 ]
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>
RTLA: Real-Time Linux Analysis tools The rtla meta-tool includes a set of commands that aims to analyze the real-time properties of Linux. Instead of testing Linux as a black box, rtla leverages kernel tracing capabilities to provide precise information about the properties and root causes of unexpected results. Installing RTLA RTLA depends on the following libraries and tools: - libtracefs - libtraceevent It also depends on python3-docutils to compile man pages. For development, we suggest the following steps for compiling rtla: $ git clone git://git.kernel.org/pub/scm/libs/libtrace/libtraceevent.git $ cd libtraceevent/ $ make $ sudo make install $ cd .. $ git clone git://git.kernel.org/pub/scm/libs/libtrace/libtracefs.git $ cd libtracefs/ $ make $ sudo make install $ cd .. $ cd $rtla_src $ make $ sudo make install For further information, please refer to the rtla man page.