Re: [PATCH v5 1/7] trace: Add trace_ipi_send_cpumask()

Peter Zijlstra
2023-03-22T10:30:04Z

On Wed, Mar 22, 2023 at 10:39:55AM +0100, Peter Zijlstra wrote:
> On Tue, Mar 07, 2023 at 02:35:52PM +0000, Valentin Schneider wrote:
> > trace_ipi_raise() is unsuitable for generically tracing IPI sources due to
> > its "reason" argument being an uninformative string (on arm64 all you get
> > is "Function call interrupts" for SMP calls).
> >
> > Add a variant of it that exports a target cpumask, a callsite and a callback.
> >
> > Signed-off-by: Valentin Schneider <vschneid@redhat.com>
> > Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
> > ---
> > include/trace/events/ipi.h | 22 ++++++++++++++++++++++
> > 1 file changed, 22 insertions(+)
> >
> > diff --git a/include/trace/events/ipi.h b/include/trace/events/ipi.h
> > index 0be71dad6ec03..b1125dc27682c 100644
> > --- a/include/trace/events/ipi.h
> > +++ b/include/trace/events/ipi.h
> > @@ -35,6 +35,28 @@ TRACE_EVENT(ipi_raise,
> > TP_printk("target_mask=%s (%s)", __get_bitmask(target_cpus), __entry->reason)
> > );
> >
> > +TRACE_EVENT(ipi_send_cpumask,
> > +
> > + TP_PROTO(const struct cpumask *cpumask, unsigned long callsite, void *callback),
> > +
> > + TP_ARGS(cpumask, callsite, callback),
> > +
> > + TP_STRUCT__entry(
> > + __cpumask(cpumask)
> > + __field(void *, callsite)
> > + __field(void *, callback)
> > + ),
> > +
> > + TP_fast_assign(
> > + __assign_cpumask(cpumask, cpumask_bits(cpumask));
> > + __entry->callsite = (void *)callsite;
> > + __entry->callback = callback;
> > + ),
> > +
> > + TP_printk("cpumask=%s callsite=%pS callback=%pS",
> > + __get_cpumask(cpumask), __entry->callsite, __entry->callback)
> > +);
>
> Would it make sense to add a variant like: ipi_send_cpu() that records a
> single cpu instead of a cpumask. A lot of sites seems to do:
> cpumask_of(cpu) for that first argument, and it seems to me it is quite
> daft to have to memcpy a full multi-word cpumask in those cases.
>
> Remember, nr_possible_cpus > 64 is quite common these days.

Something we litte bit like so...

---
Subject: trace: Add trace_ipi_send_cpu()
From: Peter Zijlstra <peterz@infradead.org>
Date: Wed Mar 22 11:28:36 CET 2023

Because copying cpumasks around when targeting a single CPU is a bit
daft...

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
include/linux/smp.h | 6 +++---
include/trace/events/ipi.h | 22 ++++++++++++++++++++++
kernel/irq_work.c | 6 ++----
kernel/smp.c | 4 ++--
4 files changed, 29 insertions(+), 9 deletions(-)

--- a/include/linux/smp.h
+++ b/include/linux/smp.h
@@ -130,9 +130,9 @@ extern void arch_smp_send_reschedule(int
* scheduler_ipi() is inline so can't be passed as callback reason, but the
* callsite IP should be sufficient for root-causing IPIs sent from here.
*/
-#define smp_send_reschedule(cpu) ({ \
- trace_ipi_send_cpumask(cpumask_of(cpu), _RET_IP_, NULL); \
- arch_smp_send_reschedule(cpu); \
+#define smp_send_reschedule(cpu) ({ \
+ trace_ipi_send_cpu(cpu, _RET_IP_, NULL); \
+ arch_smp_send_reschedule(cpu); \
})

/*
--- a/include/trace/events/ipi.h
+++ b/include/trace/events/ipi.h
@@ -35,6 +35,28 @@ TRACE_EVENT(ipi_raise,
TP_printk("target_mask=%s (%s)", __get_bitmask(target_cpus), __entry->reason)
);

+TRACE_EVENT(ipi_send_cpu,
+
+ TP_PROTO(const unsigned int cpu, unsigned long callsite, void *callback),
+
+ TP_ARGS(cpu, callsite, callback),
+
+ TP_STRUCT__entry(
+ __field(unsigned int, cpu)
+ __field(void *, callsite)
+ __field(void *, callback)
+ ),
+
+ TP_fast_assign(
+ __entry->cpu = cpu;
+ __entry->callsite = (void *)callsite;
+ __entry->callback = callback;
+ ),
+
+ TP_printk("cpu=%s callsite=%pS callback=%pS",
+ __entry->cpu, __entry->callsite, __entry->callback)
+);
+
TRACE_EVENT(ipi_send_cpumask,

TP_PROTO(const struct cpumask *cpumask, unsigned long callsite, void *callback),
--- a/kernel/irq_work.c
+++ b/kernel/irq_work.c
@@ -78,10 +78,8 @@ void __weak arch_irq_work_raise(void)

static __always_inline void irq_work_raise(struct irq_work *work)
{
- if (trace_ipi_send_cpumask_enabled() && arch_irq_work_has_interrupt())
- trace_ipi_send_cpumask(cpumask_of(smp_processor_id()),
- _RET_IP_,
- work->func);
+ if (trace_ipi_send_cpu_enabled() && arch_irq_work_has_interrupt())
+ trace_ipi_send_cpu(smp_processor_id(), _RET_IP_, work->func);

arch_irq_work_raise();
}
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -109,7 +109,7 @@ static __always_inline void
send_call_function_single_ipi(int cpu, smp_call_func_t func)
{
if (call_function_single_prep_ipi(cpu)) {
- trace_ipi_send_cpumask(cpumask_of(cpu), _RET_IP_, func);
+ trace_ipi_send_cpu(cpu, _RET_IP_, func);
arch_send_call_function_single_ipi(cpu);
}
}
@@ -348,7 +348,7 @@ void __smp_call_single_queue(int cpu, st
* even if we haven't sent the smp_call IPI yet (e.g. the stopper
* executes migration_cpu_stop() on the remote CPU).
*/
- if (trace_ipi_send_cpumask_enabled()) {
+ if (trace_ipi_send_cpu_enabled()) {
call_single_data_t *csd;
smp_call_func_t func;