Re: trace-cmd No such device Errors

[Vishal Chourasia <vishalc@linux.ibm.com>]

On Mon, May 19, 2025 at 10:39:14AM -0400, Steven Rostedt wrote:
> On Thu, 15 May 2025 02:21:13 +0530
> Vishal Chourasia <vishalc@linux.ibm.com> wrote:
> 
> > When running trace-cmd record, I encounter multiple "No such device"
> > errors due to the splice syscall failing with ENODEV for
> > /sys/kernel/tracing/per_cpu/cpuX/trace_pipe_raw files corresponding to
> > CPUs that are possible but not present.
> > 
> > Environment:
> > - Operating System: Red Hat Enterprise Linux 9.5 (Plow)
> > - Kernel: Linux 6.12.0-55.9.1.el10_0.ppc64le
> > - Architecture: ppc64le
> > - Command Executed: trace-cmd record -o /dev/null -v -e sched_switch -- sleep 1
> > - System CPU Configuration:
> >   - /sys/devices/system/cpu/possible: 0-223
> >   - /sys/devices/system/cpu/present: 0-63
> >   - /sys/kernel/tracing/per_cpu/: Contains directories cpu0 to cpu223
> 
> Thanks for the report. Could you also submit a bug report here:
> 
>   https://bugzilla.kernel.org/buglist.cgi?component=Trace-cmd%2FKernelshark&list_id=1152443&product=Tools&resolution=---
https://bugzilla.kernel.org/show_bug.cgi?id=220139
> 
> 
> > 
> > Steps to Reproduce: 
> > 1. On a system with a mismatch between possible and present CPUs (e.g.,
> >    possible: 0-223, present: 0-63). 
> > 2. Ensure /sys/kernel/tracing/per_cpu/ contains directories for all possible 
> >    CPUs (e.g., cpu0 to cpu223). 
> > 3. Run the command:
> > strace --decode-fds -kk -o strace/trace-cmd -ff -- trace-cmd record -o /dev/null -v -e sched_switch -- sleep 1
> > 4. Observe the output and strace logs.
> > 
> > Expected Behavior: trace-cmd should only attempt to access
> > trace_pipe_raw files for CPUs that are present (e.g., cpu0 to cpu63),
> > completing the recording without errors.
> 
> Can you show me what you see in /sys/kernel/tracing/tracing_cpumask
$ sudo cat /sys/kernel/tracing/tracing_cpumask
ffffffff,ffffffff,ffffffff,ffffffff,ffffffff,ffffffff,ffffffff
> 
> Thanks,
> 
> -- Steve
Thanks,

Vishal