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rtla/osnoise: Leverage IPI event filters when tracing a subset of CPUs

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Leverage the kernel event filtering infrastructure to only emit IPI events
if they target CPUs that are being traced, as specified by the -c cmdline
option.

Note that some post-processing is still required for the ipi_send_cpumask
event, as the event being emitted means *some* CPUs targeted by that event
are monitored, but not all of them - userspace has to recompute that
intersection.

Signed-off-by: Valentin Schneider <vschneid@redhat.com>
Link: https://lore.kernel.org/r/20260902123942.695822-4-vschneid@redhat.com
Signed-off-by: Tomas Glozar <tglozar@redhat.com>
This commit is contained in:
Valentin Schneider 2026-09-02 14:39:32 +02:00 committed by Tomas Glozar
parent e24c047993
commit 9ca6a1662b
1 changed files with 33 additions and 5 deletions
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38
tools/tracing/rtla/src/osnoise_top.c
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@ -303,17 +303,13 @@ osnoise_ipi_cpu_handler(struct trace_seq *s, struct tep_record *record,
struct tep_event *event, void *context)
{
struct osnoise_tool *tool;
struct osnoise_params *params;
unsigned long long dst_cpu;
struct trace_instance *trace = context;
tool = container_of(trace, struct osnoise_tool, trace);
params = to_osnoise_params(tool->params);
tep_get_field_val(s, event, "cpu", record, &dst_cpu, 1);
if (CPU_ISSET(dst_cpu, &params->common.monitored_cpus))
account_ipi(tool, dst_cpu);
account_ipi(tool, dst_cpu);
return 0;
}
@ -347,6 +343,11 @@ osnoise_ipi_cpumask_handler(struct trace_seq *s, struct tep_record *record,
return 0;
}
/*
* Despite already filtering for such an intersection, we need to compute
* the intersection here as the @cpumask field may contain non-monitored
* CPUs.
*/
CPU_AND(&cpumask_tmp_cpus, event_cpus, &params->common.monitored_cpus);
/*
@ -399,6 +400,33 @@ 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 < 0) {
err_msg("Could not set ipi_send_cpu CPU filter\n");
goto out_err;
}
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 < 0) {
err_msg("Could not set ipi_send_cpumask CPU filter\n");
goto out_err;
}
}
tep_register_event_handler(tool->trace.tep, -1, "ipi", "ipi_send_cpu",
osnoise_ipi_cpu_handler, NULL);