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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
This commit is contained in:
Leonardo Bras 2023-06-15 03:59:45 -03:00 committed by Peter Zijlstra
parent 60be49bdf1
commit 949fa3f11c
2 changed files with 64 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

45
include/trace/events/csd.h Normal file
View File

@ -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>

25
kernel/smp.c
View File

@ -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);
}