* [RFC PATCH v5 1/2] trace,smp: Add tracepoints around remotelly called functions
2023-06-15 6:59 [RFC PATCH v5 0/2] trace,smp: Add tracepoints for csd Leonardo Bras
@ 2023-06-15 6:59 ` Leonardo Bras
2023-06-15 16:42 ` Valentin Schneider
2023-06-15 6:59 ` [RFC PATCH v5 2/2] trace,smp: Add tracepoints for scheduling " Leonardo Bras
1 sibling, 1 reply; 5+ messages in thread
From: Leonardo Bras @ 2023-06-15 6:59 UTC (permalink / raw)
To: Steven Rostedt, Masami Hiramatsu, Leonardo Bras, Peter Zijlstra,
Paul E. McKenney, Juergen Gross, Valentin Schneider, Yury Norov,
Sebastian Andrzej Siewior
Cc: linux-kernel, linux-trace-kernel
The recently added ipi_send_{cpu,cpumask} tracepoints allow finding sources
of IPIs targeting CPUs running latency-sensitive applications.
For NOHZ_FULL CPUs, all IPIs are interference, and those tracepoints are
sufficient to find them and work on getting rid of them. In some setups
however, not *all* IPIs are to be suppressed, but long-running IPI
callbacks can still be problematic.
Add a pair of tracepoints to mark the start and end of processing a CSD IPI
callback, similar to what exists for softirq, workqueue or timer callbacks.
Signed-off-by: Leonardo Bras <leobras@redhat.com>
---
include/trace/events/csd.h | 45 ++++++++++++++++++++++++++++++++++++++
kernel/smp.c | 25 ++++++++++++++++-----
2 files changed, 64 insertions(+), 6 deletions(-)
create mode 100644 include/trace/events/csd.h
diff --git a/include/trace/events/csd.h b/include/trace/events/csd.h
new file mode 100644
index 000000000000..af1df5200ae6
--- /dev/null
+++ b/include/trace/events/csd.h
@@ -0,0 +1,45 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM csd
+
+#if !defined(_TRACE_CSD_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_CSD_H
+
+#include <linux/tracepoint.h>
+
+/*
+ * Tracepoints for a function which is called as an effect of smp_call_function.*
+ */
+DECLARE_EVENT_CLASS(csd_function,
+
+ TP_PROTO(smp_call_func_t func, struct __call_single_data *csd),
+
+ TP_ARGS(func, csd),
+
+ TP_STRUCT__entry(
+ __field(void *, func)
+ __field(void *, csd)
+ ),
+
+ TP_fast_assign(
+ __entry->func = func;
+ __entry->csd = csd;
+ ),
+
+ TP_printk("func=%ps, csd=%p", __entry->func, __entry->csd)
+);
+
+DEFINE_EVENT(csd_function, csd_function_entry,
+ TP_PROTO(smp_call_func_t func, struct __call_single_data *csd),
+ TP_ARGS(func, csd)
+);
+
+DEFINE_EVENT(csd_function, csd_function_exit,
+ TP_PROTO(smp_call_func_t func, struct __call_single_data *csd),
+ TP_ARGS(func, csd)
+);
+
+#endif /* _TRACE_CSD_H */
+
+/* This part must be outside protection */
+#include <trace/define_trace.h>
diff --git a/kernel/smp.c b/kernel/smp.c
index 919387be6d4e..7199b5a22043 100644
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -27,6 +27,9 @@
#include <linux/jump_label.h>
#include <trace/events/ipi.h>
+#define CREATE_TRACE_POINTS
+#include <trace/events/csd.h>
+#undef CREATE_TRACE_POINTS
#include "smpboot.h"
#include "sched/smp.h"
@@ -121,6 +124,14 @@ send_call_function_ipi_mask(struct cpumask *mask)
arch_send_call_function_ipi_mask(mask);
}
+static __always_inline void
+csd_do_func(smp_call_func_t func, void *info, struct __call_single_data *csd)
+{
+ trace_csd_function_entry(func, csd);
+ func(info);
+ trace_csd_function_exit(func, csd);
+}
+
#ifdef CONFIG_CSD_LOCK_WAIT_DEBUG
static DEFINE_STATIC_KEY_MAYBE(CONFIG_CSD_LOCK_WAIT_DEBUG_DEFAULT, csdlock_debug_enabled);
@@ -375,7 +386,7 @@ static int generic_exec_single(int cpu, call_single_data_t *csd)
csd_lock_record(csd);
csd_unlock(csd);
local_irq_save(flags);
- func(info);
+ csd_do_func(func, info, NULL);
csd_lock_record(NULL);
local_irq_restore(flags);
return 0;
@@ -477,7 +488,7 @@ static void __flush_smp_call_function_queue(bool warn_cpu_offline)
}
csd_lock_record(csd);
- func(info);
+ csd_do_func(func, info, csd);
csd_unlock(csd);
csd_lock_record(NULL);
} else {
@@ -508,7 +519,7 @@ static void __flush_smp_call_function_queue(bool warn_cpu_offline)
csd_lock_record(csd);
csd_unlock(csd);
- func(info);
+ csd_do_func(func, info, csd);
csd_lock_record(NULL);
} else if (type == CSD_TYPE_IRQ_WORK) {
irq_work_single(csd);
@@ -522,8 +533,10 @@ static void __flush_smp_call_function_queue(bool warn_cpu_offline)
/*
* Third; only CSD_TYPE_TTWU is left, issue those.
*/
- if (entry)
- sched_ttwu_pending(entry);
+ if (entry) {
+ csd = llist_entry(entry, typeof(*csd), node.llist);
+ csd_do_func(sched_ttwu_pending, entry, csd);
+ }
}
@@ -816,7 +829,7 @@ static void smp_call_function_many_cond(const struct cpumask *mask,
unsigned long flags;
local_irq_save(flags);
- func(info);
+ csd_do_func(func, info, NULL);
local_irq_restore(flags);
}
--
2.41.0
^ permalink raw reply related [flat|nested] 5+ messages in thread* [RFC PATCH v5 2/2] trace,smp: Add tracepoints for scheduling remotelly called functions
2023-06-15 6:59 [RFC PATCH v5 0/2] trace,smp: Add tracepoints for csd Leonardo Bras
2023-06-15 6:59 ` [RFC PATCH v5 1/2] trace,smp: Add tracepoints around remotelly called functions Leonardo Bras
@ 2023-06-15 6:59 ` Leonardo Bras
2023-06-15 16:42 ` Valentin Schneider
1 sibling, 1 reply; 5+ messages in thread
From: Leonardo Bras @ 2023-06-15 6:59 UTC (permalink / raw)
To: Steven Rostedt, Masami Hiramatsu, Leonardo Bras, Peter Zijlstra,
Paul E. McKenney, Juergen Gross, Valentin Schneider, Yury Norov,
Sebastian Andrzej Siewior
Cc: linux-kernel, linux-trace-kernel
Add a tracepoint for when a CSD is queued to a remote CPU's
call_single_queue. This allows finding exactly which CPU queued a given CSD
when looking at a csd_function_{entry,exit} event, and also enables us to
accurately measure IPI delivery time with e.g. a synthetic event:
$ echo 'hist:keys=cpu,csd.hex:ts=common_timestamp.usecs' >\
/sys/kernel/tracing/events/smp/csd_queue_cpu/trigger
$ echo 'csd_latency unsigned int dst_cpu; unsigned long csd; u64 time' >\
/sys/kernel/tracing/synthetic_events
$ echo \
'hist:keys=common_cpu,csd.hex:'\
'time=common_timestamp.usecs-$ts:'\
'onmatch(smp.csd_queue_cpu).trace(csd_latency,common_cpu,csd,$time)' >\
/sys/kernel/tracing/events/smp/csd_function_entry/trigger
$ trace-cmd record -e 'synthetic:csd_latency' hackbench
$ trace-cmd report
<...>-467 [001] 21.824263: csd_queue_cpu: cpu=0 callsite=try_to_wake_up+0x2ea func=sched_ttwu_pending csd=0xffff8880076148b8
<...>-467 [001] 21.824280: ipi_send_cpu: cpu=0 callsite=try_to_wake_up+0x2ea callback=generic_smp_call_function_single_interrupt+0x0
<...>-489 [000] 21.824299: csd_function_entry: func=sched_ttwu_pending csd=0xffff8880076148b8
<...>-489 [000] 21.824320: csd_latency: dst_cpu=0, csd=18446612682193848504, time=36
Suggested-by: Valentin Schneider <vschneid@redhat.com>
Signed-off-by: Leonardo Bras <leobras@redhat.com>
---
include/trace/events/csd.h | 27 +++++++++++++++++++++++++++
kernel/smp.c | 16 +++++-----------
2 files changed, 32 insertions(+), 11 deletions(-)
diff --git a/include/trace/events/csd.h b/include/trace/events/csd.h
index af1df5200ae6..67e9d01f80c2 100644
--- a/include/trace/events/csd.h
+++ b/include/trace/events/csd.h
@@ -7,6 +7,33 @@
#include <linux/tracepoint.h>
+TRACE_EVENT(csd_queue_cpu,
+
+ TP_PROTO(const unsigned int cpu,
+ unsigned long callsite,
+ smp_call_func_t func,
+ struct __call_single_data *csd),
+
+ TP_ARGS(cpu, callsite, func, csd),
+
+ TP_STRUCT__entry(
+ __field(unsigned int, cpu)
+ __field(void *, callsite)
+ __field(void *, func)
+ __field(void *, csd)
+ ),
+
+ TP_fast_assign(
+ __entry->cpu = cpu;
+ __entry->callsite = (void *)callsite;
+ __entry->func = func;
+ __entry->csd = csd;
+ ),
+
+ TP_printk("cpu=%u callsite=%pS func=%ps csd=%p",
+ __entry->cpu, __entry->callsite, __entry->func, __entry->csd)
+ );
+
/*
* Tracepoints for a function which is called as an effect of smp_call_function.*
*/
diff --git a/kernel/smp.c b/kernel/smp.c
index 7199b5a22043..692dbb400701 100644
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -340,7 +340,7 @@ void __smp_call_single_queue(int cpu, struct llist_node *node)
* 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_cpu_enabled()) {
+ if (trace_csd_queue_cpu_enabled()) {
call_single_data_t *csd;
smp_call_func_t func;
@@ -348,7 +348,7 @@ void __smp_call_single_queue(int cpu, struct llist_node *node)
func = CSD_TYPE(csd) == CSD_TYPE_TTWU ?
sched_ttwu_pending : csd->func;
- trace_ipi_send_cpu(cpu, _RET_IP_, func);
+ trace_csd_queue_cpu(cpu, _RET_IP_, func, csd);
}
/*
@@ -741,7 +741,7 @@ static void smp_call_function_many_cond(const struct cpumask *mask,
int cpu, last_cpu, this_cpu = smp_processor_id();
struct call_function_data *cfd;
bool wait = scf_flags & SCF_WAIT;
- int nr_cpus = 0, nr_queued = 0;
+ int nr_cpus = 0;
bool run_remote = false;
bool run_local = false;
@@ -799,21 +799,15 @@ static void smp_call_function_many_cond(const struct cpumask *mask,
csd->node.src = smp_processor_id();
csd->node.dst = cpu;
#endif
+ trace_csd_queue_cpu(cpu, _RET_IP_, func, csd);
+
if (llist_add(&csd->node.llist, &per_cpu(call_single_queue, cpu))) {
__cpumask_set_cpu(cpu, cfd->cpumask_ipi);
nr_cpus++;
last_cpu = cpu;
}
- nr_queued++;
}
- /*
- * Trace each smp_function_call_*() as an IPI, actual IPIs
- * will be traced with func==generic_smp_call_function_single_ipi().
- */
- if (nr_queued)
- trace_ipi_send_cpumask(cfd->cpumask, _RET_IP_, func);
-
/*
* Choose the most efficient way to send an IPI. Note that the
* number of CPUs might be zero due to concurrent changes to the
--
2.41.0
^ permalink raw reply related [flat|nested] 5+ messages in thread