On 30/06/26 12:14, Tomas Glozar wrote:
> st 17. 6. 2026 v 15:18 odesÃlatel Valentin Schneider
> <[email protected]> napsal:
>> @@ -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.
>> + 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/[email protected]/T/#u
>
Makes sense, will do.
>> + }
>> +
>> +
>> + 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.
>
>> + }
>> +
>> 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
