On 30/06/26 12:14, Tomas Glozar wrote:

st 17. 6. 2026 v 15:18 odesílatel Valentin Schneider
[off-list ref] napsal:

quoted

@@ -406,6 +408,33 @@ struct osnoise_tool *osnoise_init_top(struct common_params *params)
                goto out_err;
        }

+       /*
+        * If tracing on a subset of possible CPUs, leverage the kernel filtering
+        * infrastructure to only generate events on traced CPUs.
+        */
+       if (params->cpus) {
+               char filter[MAX_PATH];
+
+               snprintf(filter, ARRAY_SIZE(filter), "cpu & CPUS{%s}\n", params->cpus);
+               retval = tracefs_event_file_write(tool->trace.inst,
+                                                 "ipi", "ipi_send_cpu", "filter",
+                                                 filter);
+               if (retval) {

retval is the number of bytes written here, so this should be "retval
< 0" like in trace_event_enable_filter() in trace.c. Same below.

According to the docstring:

 * Return 0 on success, and -1 on error.

but regardless yes that should be a '< 0' check to match existing code.

quoted

+                       err_msg("Could not set ipi_send_cpu CPU filter\n");
+                       goto out_err;

It would be useful to have --ipi work even on older kernels that don't
yet have your cpumask trace event filter patchset [1], for example, by
printing a debug message that filtering is disabled and setting a flag
instead of erroring out here. Then the code in
osnoise_ipi_cpu_handler() can preserve the CPU_ISSET check if the flag
is set.

As --ipi is optional, we can choose to only support it on newer
kernels, but it would be nice to have it working without the filter,
too.

[1] https://lore.kernel.org/linux-trace-kernel/20230707172155.70873-1-vschneid@redhat.com/T/#u (local)

Makes sense, will do.

quoted

+               }
+
+
+               snprintf(filter, ARRAY_SIZE(filter), "cpumask & CPUS{%s}\n", params->cpus);
+               retval = tracefs_event_file_write(tool->trace.inst,
+                                                 "ipi", "ipi_send_cpumask", "filter",
+                                                 filter);
+               if (retval) {
+                       err_msg("Could not set ipi_send_cpumask CPU filter\n");
+                       goto out_err;
+               }

Same two comments above apply here.

quoted

+       }
+
        tep_register_event_handler(tool->trace.tep, -1, "ipi", "ipi_send_cpu",
                                   osnoise_ipi_cpu_handler, NULL);

--
2.54.0

I was thinking that it might make sense to enable the filters also for
the trace output instance. On the other hand, it would make it
difficult to enable the event without the filter then, as specifying
"-e ipi" or similar only re-enables the event but does not remove the
filter. Maybe the better idea is to implement an option to filter any
event enabled through -e/--event only to the measurement CPU, as a
separate feature.

I had actually forgotten about applying the filters for the output
instance... I'll look into it.

Tomas