Questions tagged [ftrace]
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23 questions
1 vote
0 answers
123 views
Is the TASK-PID in trace-cmd output the TID of the thread handling TAP interface I/O?
I'm working on an networking lab tool leveraging QEMU-based VM virtualization and docker technology to run VMs and containers respectively on a Linux host. The underlying lab connectivity is ...
- 385
0 votes
1 answer
79 views
Failed to register hook to tracepoint of signal_generate in Linux?
I am testing FTRACE in Linux VM (ubuntu 24.04) the kernel is Linux VirtualBox 6.11.0-26-generic. I wrote a kernel module to register a hook (probe) to kernel tracepoint of signal_generate, here is the ...
- 651
0 votes
0 answers
25 views
Why does comm stay as the old name even after multiple task_rename and sched_process_exec events?
I am analyzing some trace-cmd (event) output filtered for some specific PID. The workflow is as follows (parse.py is just a custom python to parse for specific PIDs, $EVENTS_ARGS is just a list of the ...
2 votes
0 answers
36 views
Task name shown as <...> in the output of EBPF program
I wrote a simple EBPF program which prints a message when the execve system call is invoked. I print the message using the bpf_trace_printk function. In the output, the task name for some processes is ...
1 vote
0 answers
87 views
How to interpert hwlat trace results on an ARM Cortex-A7?
I’m working with an STM32MP157D-DK1, trying to use the hwlat tracer for the board's arm Cortex-A7 CPU, to check for typical hardware latency. The following attempt was made to use the hwlat tracer on ...
- 11
4 votes
1 answer
485 views
When (and how) are file permission/access decisions made in kernel space?
(I think) I have a relatively good understanding of how Linux permissions work - traditional Unix DAC permissions, and how they're represented, security context in relation to processes (i.e. cred ...
- 129
2 votes
0 answers
209 views
What's the difference between ftrace and blktrace tracepoints?
For instance, we have /sys/kernel/debug/tracing/events/block/block_bio_complete and block_rq_complete which is basically IO completion trace points for ftrace, I believe. Using sudo blktrace -d /dev/...
- 263
1 vote
0 answers
57 views
How to get the cpu number of a trace event in a custom probe function?
I am registering a probe function for trace events using a Kernel module. For eg the probe function for the trace event sched_kthread_stop would be: void handle_kthread_stop(void *data, struct ...
2 votes
1 answer
215 views
Multiple Tracing Events Readers
Question Does the tracing pipes in Linux, for tracing events, accepts simultaneous readers? Context I am trying to get traces from the RAS subsystem while running some benchmarks. This subsystem ...
3 votes
0 answers
350 views
Linux task state different in /proc/pid/stat compared to Ftrace output of sched events
I'm trying to trace the flow of a piece of code just to understand the points where the tasks go into D/S/R states (uninterruptible/interruptible/running). I do understand the meaning of each state, ...
- 151
2 votes
1 answer
261 views
How can I send dmesg printout to ftrace subsystem?
How can I send dmesg printout to ftrace subsystem? I like correlate the dmesg msg with the functions call graph in ftrace. Thanks
- 141
1 vote
1 answer
415 views
How writing in debugfs controls ftrace?
Ftrace is controlled by manipulating the debug fs files. But how is it possible ? How kernel be aware of writing in this files and start its required actions?for exmple if 1 is written to tracing_on , ...
- 11
5 votes
2 answers
888 views
Change format of syscall event trace output to ftrace
I enabled ftrace event tracing for sys_enter_openat syscall. The respective output format given at events/syscalls/sys_enter_openat/format is print fmt: "dfd: 0x%08lx, filename: 0x%08lx, flags: 0x%...
- 151
0 votes
1 answer
200 views
Performance reduction activating trace-functionality in kernel
Is there any performance reduction to be expected from just activating trace (ftrace) functionality in the Linux kernel, but not using it at run time?
- 381
0 votes
1 answer
270 views
functions folder in trace_stat folder of ftrace
I am learning ftrace, I read from the following link that I can enable function profiling using the 'function_profile_enabled' file. mount -t tracefs nodev /sys/kernel/tracing cd /sys/kernel/tracing ...
- 311