[PATCH v2 31/35] tracing: support lazy resched

Ankur Arora
2024-05-28T00:37:16Z

trace_entry::flags is full, so reuse the TRACE_FLAG_IRQS_NOSUPPORT
bit for this. The flag is safe to reuse since it is only used in
old archs that don't support lockdep irq tracing.

Also, now that we have a variety of need-resched combinations, document
these in the tracing headers.

Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Originally-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/lkml/87jzshhexi.ffs@tglx/
Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
---
include/linux/trace_events.h | 6 +++---
kernel/trace/trace.c | 28 ++++++++++++++++++----------
kernel/trace/trace_output.c | 16 ++++++++++++++--
3 files changed, 35 insertions(+), 15 deletions(-)

diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
index 6f9bdfb09d1d..329002785b4d 100644
--- a/include/linux/trace_events.h
+++ b/include/linux/trace_events.h
@@ -184,7 +184,7 @@ unsigned int tracing_gen_ctx_irq_test(unsigned int irqs_status);

enum trace_flag_type {
TRACE_FLAG_IRQS_OFF = 0x01,
- TRACE_FLAG_IRQS_NOSUPPORT = 0x02,
+ TRACE_FLAG_NEED_RESCHED_LAZY = 0x02,
TRACE_FLAG_NEED_RESCHED = 0x04,
TRACE_FLAG_HARDIRQ = 0x08,
TRACE_FLAG_SOFTIRQ = 0x10,
@@ -211,11 +211,11 @@ static inline unsigned int tracing_gen_ctx(void)

static inline unsigned int tracing_gen_ctx_flags(unsigned long irqflags)
{
- return tracing_gen_ctx_irq_test(TRACE_FLAG_IRQS_NOSUPPORT);
+ return tracing_gen_ctx_irq_test(0);
}
static inline unsigned int tracing_gen_ctx(void)
{
- return tracing_gen_ctx_irq_test(TRACE_FLAG_IRQS_NOSUPPORT);
+ return tracing_gen_ctx_irq_test(0);
}
#endif

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index ed229527be05..7941e9ec979a 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -2513,6 +2513,8 @@ unsigned int tracing_gen_ctx_irq_test(unsigned int irqs_status)

if (__tif_need_resched(RESCHED_NOW))
trace_flags |= TRACE_FLAG_NEED_RESCHED;
+ if (__tif_need_resched(RESCHED_LAZY))
+ trace_flags |= TRACE_FLAG_NEED_RESCHED_LAZY;
if (test_preempt_need_resched())
trace_flags |= TRACE_FLAG_PREEMPT_RESCHED;
return (trace_flags << 16) | (min_t(unsigned int, pc & 0xff, 0xf)) |
@@ -4096,17 +4098,23 @@ unsigned long trace_total_entries(struct trace_array *tr)
return entries;
}

+#ifdef CONFIG_PREEMPT_AUTO
+#define NR_LEGEND "l: lazy, n: now, p: preempt, b: l|n, L: l|p, N: n|p, B: l|n|p"
+#else
+#define NR_LEGEND "n: now, p: preempt, N: n|p"
+#endif
+
static void print_lat_help_header(struct seq_file *m)
{
- seq_puts(m, "# _------=> CPU# \n"
- "# / _-----=> irqs-off/BH-disabled\n"
- "# | / _----=> need-resched \n"
- "# || / _---=> hardirq/softirq \n"
- "# ||| / _--=> preempt-depth \n"
- "# |||| / _-=> migrate-disable \n"
- "# ||||| / delay \n"
- "# cmd pid |||||| time | caller \n"
- "# \\ / |||||| \\ | / \n");
+ seq_printf(m, "# _------=> CPU# \n"
+ "# / _-----=> irqs-off/BH-disabled\n"
+ "# | / _----=> need-resched ( %s ) \n"
+ "# || / _---=> hardirq/softirq \n"
+ "# ||| / _--=> preempt-depth \n"
+ "# |||| / _-=> migrate-disable \n"
+ "# ||||| / delay \n"
+ "# cmd pid |||||| time | caller \n"
+ "# \\ / |||||| \\ | / \n", NR_LEGEND);
}

static void print_event_info(struct array_buffer *buf, struct seq_file *m)
@@ -4141,7 +4149,7 @@ static void print_func_help_header_irq(struct array_buffer *buf, struct seq_file
print_event_info(buf, m);

seq_printf(m, "# %.*s _-----=> irqs-off/BH-disabled\n", prec, space);
- seq_printf(m, "# %.*s / _----=> need-resched\n", prec, space);
+ seq_printf(m, "# %.*s / _----=> need-resched ( %s )\n", prec, space, NR_LEGEND);
seq_printf(m, "# %.*s| / _---=> hardirq/softirq\n", prec, space);
seq_printf(m, "# %.*s|| / _--=> preempt-depth\n", prec, space);
seq_printf(m, "# %.*s||| / _-=> migrate-disable\n", prec, space);
diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
index d8b302d01083..4f58a196e14c 100644
--- a/kernel/trace/trace_output.c
+++ b/kernel/trace/trace_output.c
@@ -460,17 +460,29 @@ int trace_print_lat_fmt(struct trace_seq *s, struct trace_entry *entry)
(entry->flags & TRACE_FLAG_IRQS_OFF && bh_off) ? 'D' :
(entry->flags & TRACE_FLAG_IRQS_OFF) ? 'd' :
bh_off ? 'b' :
- (entry->flags & TRACE_FLAG_IRQS_NOSUPPORT) ? 'X' :
+ !IS_ENABLED(CONFIG_TRACE_IRQFLAGS_SUPPORT) ? 'X' :
'.';

- switch (entry->flags & (TRACE_FLAG_NEED_RESCHED |
+ switch (entry->flags & (TRACE_FLAG_NEED_RESCHED | TRACE_FLAG_NEED_RESCHED_LAZY |
TRACE_FLAG_PREEMPT_RESCHED)) {
+ case TRACE_FLAG_NEED_RESCHED | TRACE_FLAG_NEED_RESCHED_LAZY | TRACE_FLAG_PREEMPT_RESCHED:
+ need_resched = 'B';
+ break;
case TRACE_FLAG_NEED_RESCHED | TRACE_FLAG_PREEMPT_RESCHED:
need_resched = 'N';
break;
+ case TRACE_FLAG_NEED_RESCHED_LAZY | TRACE_FLAG_PREEMPT_RESCHED:
+ need_resched = 'L';
+ break;
+ case TRACE_FLAG_NEED_RESCHED | TRACE_FLAG_NEED_RESCHED_LAZY:
+ need_resched = 'b';
+ break;
case TRACE_FLAG_NEED_RESCHED:
need_resched = 'n';
break;
+ case TRACE_FLAG_NEED_RESCHED_LAZY:
+ need_resched = 'l';
+ break;
case TRACE_FLAG_PREEMPT_RESCHED:
need_resched = 'p';
break;
--
2.31.1