Messages in this thread Patch in this message | | | Date | Fri, 18 Nov 2022 10:12:43 +0100 | From | Peter Zijlstra <> | Subject | Re: [RFC PATCH v2 8/8] sched, smp: Trace smp callback causing an IPI |
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On Thu, Nov 17, 2022 at 02:45:29PM +0000, Valentin Schneider wrote:
> > + if (trace_ipi_send_cpumask_enabled()) { > > + call_single_data_t *csd; > > + smp_call_func_t func; > > + > > + csd = container_of(node, call_single_data_t, node.llist); > > + > > + func = sched_ttwu_pending; > > + if (CSD_TYPE(csd) != CSD_TYPE_TTWU) > > + func = csd->func; > > + > > + if (raw_smp_call_single_queue(cpu, node)) > > + trace_ipi_send_cpumask(cpumask_of(cpu), _RET_IP_, func); > > So I went with the tracepoint being placed *before* the actual IPI gets > sent to have a somewhat sane ordering between trace_ipi_send_cpumask() and > e.g. trace_call_function_single_entry(). > > Packaging the call_single_queue logic makes the code less horrible, but it > does mix up the event ordering...
Keeps em sharp ;-)
> > + return; > > + } > > + > > + raw_smp_call_single_queue(cpu, node); > > } > > > > /* > > @@ -983,10 +1017,13 @@ static void smp_call_function_many_cond( > > * number of CPUs might be zero due to concurrent changes to the > > * provided mask. > > */ > > - if (nr_cpus == 1) > > + if (nr_cpus == 1) { > > + trace_ipi_send_cpumask(cpumask_of(last_cpu), _RET_IP_, func); > > send_call_function_single_ipi(last_cpu); > > This'll yield an IPI event even if no IPI is sent due to the idle task > polling, no?
Oh, right..
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