trace,smp: Add tracepoints around remotelly called functions

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>
Tested-and-reviewed-by: Valentin Schneider <vschneid@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20230615065944.188876-5-leobras@redhat.com

diff --git a/include/trace/events/csd.h b/include/trace/events/csd.h
new file mode 100644 (file)
index 0000000..af1df52
--- /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 71dce748dbf093325f0046ffec1258a95108cba8..1fa01a83fd83ceb4c0b5f5617ca57b8917b84e6b 100644 (file)
--- 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, struct __call_single_data *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);
        }