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Date: Wed, 10 May 2023 20:05:21 -0300
From: Leonardo Bras Soares Passos <leobras@...hat.com>
To: Steven Rostedt <rostedt@...dmis.org>,
Masami Hiramatsu <mhiramat@...nel.org>,
Leonardo Bras <leobras@...hat.com>,
Peter Zijlstra <peterz@...radead.org>,
"Paul E. McKenney" <paulmck@...nel.org>,
Juergen Gross <jgross@...e.com>,
Valentin Schneider <vschneid@...hat.com>,
Yury Norov <yury.norov@...il.com>,
Zhen Lei <thunder.leizhen@...wei.com>,
Marcelo Tosatti <mtosatti@...hat.com>,
Thomas Gleixner <tglx@...utronix.de>,
Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
Nadav Amit <namit@...are.com>,
Chen Zhongjin <chenzhongjin@...wei.com>,
Daniel Bristot de Oliveira <bristot@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v2 1/1] trace,smp: Add tracepoints around remotelly
called functions
On Wed, May 10, 2023 at 7:16 PM Leonardo Bras <leobras@...hat.com> wrote:
>
> When running RT workloads in isolated CPUs, many cases of deadline misses
> are caused by remote CPU requests such as smp_call_function*().
>
> For those cases, having the names of those functions running around the
> deadline miss moment could help (a lot) finding a target for the next
> improvements.
>
> Add tracepoints for acquiring the function name & csd before entry and
> after returning from the remote-cpu requested function.
>
> Also, add tracepoints on the remote cpus requesting them.
>
> Signed-off-by: Leonardo Bras <leobras@...hat.com>
> ---
>
> Changes since RFCv1:
> - Implemented trace_csd_queue_cpu() as suggested by Valentin Schneider
> - Using EVENT_CLASS in order to avoid duplication
> - Introduced new helper: csd_do_func()
> - Name change from smp_call_function_* to csd_function_*
> - Rebased on top of torvalds/master
>
> include/trace/events/smp.h | 72 ++++++++++++++++++++++++++++++++++++++
> kernel/smp.c | 41 +++++++++++++---------
> 2 files changed, 96 insertions(+), 17 deletions(-)
> create mode 100644 include/trace/events/smp.h
>
> diff --git a/include/trace/events/smp.h b/include/trace/events/smp.h
> new file mode 100644
> index 000000000000..5fd75399d3f1
> --- /dev/null
> +++ b/include/trace/events/smp.h
> @@ -0,0 +1,72 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#undef TRACE_SYSTEM
> +#define TRACE_SYSTEM smp
> +
> +#if !defined(_TRACE_SMP_H) || defined(TRACE_HEADER_MULTI_READ)
> +#define _TRACE_SMP_H
> +
> +#include <linux/tracepoint.h>
> +
> +TRACE_EVENT(csd_queue_cpu,
> +
> + TP_PROTO(const unsigned int cpu,
> + unsigned long callsite,
> + smp_call_func_t func,
> + call_single_data_t *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.*
> + */
> +DECLARE_EVENT_CLASS(csd_function,
> +
> + TP_PROTO(smp_call_func_t func, call_single_data_t *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("function %ps, csd = %p", __entry->func, __entry->csd)
> +);
> +
> +DEFINE_EVENT(csd_function, csd_function_entry,
> + TP_PROTO(smp_call_func_t func, call_single_data_t *csd),
> + TP_ARGS(func, csd),
> +);
> +
> +DEFINE_EVENT(csd_function, csd_function_exit,
> + TP_PROTO(smp_call_func_t func, call_single_data_t *csd),
> + TP_ARGS(func, csd),
> +);
> +
> +#endif /* _TRACE_SMP_H */
> +
> +/* This part must be outside protection */
> +#include <trace/define_trace.h>
> diff --git a/kernel/smp.c b/kernel/smp.c
> index ab3e5dad6cfe..a34aa2b92050 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/smp.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, call_single_data_t *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);
> @@ -329,7 +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;
>
> @@ -337,7 +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);
> }
>
> /*
> @@ -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, csd);
> 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);
> + }
> }
>
>
> @@ -728,7 +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;
>
> @@ -786,21 +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
> @@ -816,7 +823,7 @@ 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, csd);
> local_irq_restore(flags);
> }
>
> --
> 2.40.1
>
Argh, I accidentally sent an unfinished patch, sorry about that.
Please disconsider above v2, and review the v3 instead:
https://lore.kernel.org/lkml/20230510230128.150384-1-leobras@redhat.com/
Leo
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