[RFC][PATCH] tracing: Add __cpumask() macro to trace events to record cpumasks

Steven Rostedt
2014-05-06T17:22:48Z

Being able to show a cpumask of events can be useful as some events
may affect only some CPUs. There is no standard way to record the
cpumask and converting it to a string is rather expensive during
the trace as traces happen in hotpaths. It would be better to record
the raw event mask and be able to parse it at print time.

The following macros were added for use with the TRACE_EVENT() macro:

__cpumask()
__assign_cpumask()
__get_cpumask()

To test this, I added this to the sched_migrate_task event, which
looked like this:

TRACE_EVENT(sched_migrate_task,

TP_PROTO(struct task_struct *p, int dest_cpu, const struct cpumask *cpus),

TP_ARGS(p, dest_cpu, cpus),

TP_STRUCT__entry(
__array( char, comm, TASK_COMM_LEN )
__field( pid_t, pid )
__field( int, prio )
__field( int, orig_cpu )
__field( int, dest_cpu )
__cpumask( cpumask, cpus )
),

TP_fast_assign(
memcpy(__entry->comm, p->comm, TASK_COMM_LEN);
__entry->pid = p->pid;
__entry->prio = p->prio;
__entry->orig_cpu = task_cpu(p);
__entry->dest_cpu = dest_cpu;
__assign_cpumask(cpumask, cpus);
),

TP_printk("comm=%s pid=%d prio=%d orig_cpu=%d dest_cpu=%d cpumask=%s",
__entry->comm, __entry->pid, __entry->prio,
__entry->orig_cpu, __entry->dest_cpu,
__get_cpumask(cpumask))
);

With the output of:

ksmtuned-3613 [003] d..2 485.220508: sched_migrate_task: comm=ksmtuned pid=3615 prio=120 orig_cpu=3 dest_cpu=2 cpumask=00000000,0000000f
migration/1-13 [001] d..5 485.221202: sched_migrate_task: comm=ksmtuned pid=3614 prio=120 orig_cpu=1 dest_cpu=0 cpumask=00000000,0000000f
awk-3615 [002] d.H5 485.221747: sched_migrate_task: comm=rcu_preempt pid=7 prio=120 orig_cpu=0 dest_cpu=1 cpumask=00000000,000000ff
migration/2-18 [002] d..5 485.222062: sched_migrate_task: comm=ksmtuned pid=3615 prio=120 orig_cpu=2 dest_cpu=3 cpumask=00000000,0000000f

Link: http://lkml.kernel.org/r/1399377998-14870-6-git-send-email-javi.merino@arm.com

Suggested-by: Javi Merino <javi.merino@arm.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---

Note, the tools/lib/traceevent will need to be updated to handle the
new __get_cpumask() macro in the TP_printk().

---
include/linux/ftrace_event.h | 4 ++++
include/linux/trace_seq.h | 10 ++++++++
include/trace/ftrace.h | 57 +++++++++++++++++++++++++++++++++++++++++++-
kernel/trace/trace_output.c | 43 +++++++++++++++++++++++++++++++++
4 files changed, 113 insertions(+), 1 deletion(-)

diff --git a/include/linux/ftrace_event.h b/include/linux/ftrace_event.h
index d16da3e..f68ae9b 100644
--- a/include/linux/ftrace_event.h
+++ b/include/linux/ftrace_event.h
@@ -7,6 +7,7 @@
#include <linux/percpu.h>
#include <linux/hardirq.h>
#include <linux/perf_event.h>
+#include <linux/cpumask.h>
#include <linux/tracepoint.h>

struct trace_array;
@@ -38,6 +39,9 @@ const char *ftrace_print_symbols_seq_u64(struct trace_seq *p,
*symbol_array);
#endif

+const char *ftrace_print_cpumask_seq(struct trace_seq *p, void *cpumask_ptr,
+ unsigned int cpumask_size);
+
const char *ftrace_print_hex_seq(struct trace_seq *p,
const unsigned char *buf, int len);

diff --git a/include/linux/trace_seq.h b/include/linux/trace_seq.h
index a32d86e..052b675 100644
--- a/include/linux/trace_seq.h
+++ b/include/linux/trace_seq.h
@@ -46,6 +46,9 @@ extern int trace_seq_putmem_hex(struct trace_seq *s, const void *mem,
extern void *trace_seq_reserve(struct trace_seq *s, size_t len);
extern int trace_seq_path(struct trace_seq *s, const struct path *path);

+extern int trace_seq_cpumask(struct trace_seq *s, const unsigned long *maskp,
+ int nmaskbits);
+
#else /* CONFIG_TRACING */
static inline int trace_seq_printf(struct trace_seq *s, const char *fmt, ...)
{
@@ -57,6 +60,13 @@ trace_seq_bprintf(struct trace_seq *s, const char *fmt, const u32 *binary)
return 0;
}

+static inline int
+trace_seq_cpumask(struct trace_seq *s, const unsigned long *maskp,
+ int nmaskbits)
+{
+ return 0;
+}
+
static inline int trace_print_seq(struct seq_file *m, struct trace_seq *s)
{
return 0;
diff --git a/include/trace/ftrace.h b/include/trace/ftrace.h
index 0a1a4f7..ff3c64e 100644
--- a/include/trace/ftrace.h
+++ b/include/trace/ftrace.h
@@ -53,6 +53,9 @@
#undef __string
#define __string(item, src) __dynamic_array(char, item, -1)

+#undef __cpumask
+#define __cpumask(item, src) __dynamic_array(char, item, -1)
+
#undef TP_STRUCT__entry
#define TP_STRUCT__entry(args...) args

@@ -128,6 +131,9 @@
#undef __string
#define __string(item, src) __dynamic_array(char, item, -1)

+#undef __string
+#define __string(item, src) __dynamic_array(unsigned long, item, -1)
+
#undef DECLARE_EVENT_CLASS
#define DECLARE_EVENT_CLASS(call, proto, args, tstruct, assign, print) \
struct ftrace_data_offsets_##call { \
@@ -200,6 +206,15 @@
#undef __get_str
#define __get_str(field) (char *)__get_dynamic_array(field)

+#undef __get_cpumask
+#define __get_cpumask(field) \
+ ({ \
+ void *__cpumask = __get_dynamic_array(field); \
+ unsigned int __cpumask_size; \
+ __cpumask_size = (__entry->__data_loc_##field >> 16) & 0xffff; \
+ ftrace_print_cpumask_seq(p, __cpumask, __cpumask_size); \
+ })
+
#undef __print_flags
#define __print_flags(flag, delim, flag_array...) \
({ \
@@ -322,6 +337,9 @@ static struct trace_event_functions ftrace_event_type_funcs_##call = { \
#undef __string
#define __string(item, src) __dynamic_array(char, item, -1)

+#undef __cpumask
+#define __cpumask(item, src) __dynamic_array(unsigned long, item, -1)
+
#undef DECLARE_EVENT_CLASS
#define DECLARE_EVENT_CLASS(call, proto, args, tstruct, func, print) \
static int notrace __init \
@@ -372,6 +390,29 @@ ftrace_define_fields_##call(struct ftrace_event_call *event_call) \
#define __string(item, src) __dynamic_array(char, item, \
strlen((src) ? (const char *)(src) : "(null)") + 1)

+/*
+ * __cpumask_size_in_bytes_raw is the number of bytes needed to hold
+ * num_possible_cpus().
+ */
+#define __cpumask_size_in_bytes_raw \
+ ((num_possible_cpus() + 7) / 8)
+
+#define __cpumask_size_in_longs \
+ ((__cpumask_size_in_bytes_raw + ((BITS_PER_LONG / 8) - 1)) \
+ / (BITS_PER_LONG / 8))
+
+/*
+ * __cpumask_size_in_bytes is the number of bytes needed to hold
+ * num_possible_cpus() padded out to the nearest long. This is what
+ * is saved in the buffer, just to be consistent.
+ */
+#define __cpumask_size_in_bytes \
+ (__cpumask_size_in_longs * (BITS_PER_LONG / 8))
+
+#undef __cpumask
+#define __cpumask(item, src) __dynamic_array(unsigned long, item, \
+ __cpumask_size_in_longs)
+
#undef DECLARE_EVENT_CLASS
#define DECLARE_EVENT_CLASS(call, proto, args, tstruct, assign, print) \
static inline notrace int ftrace_get_offsets_##call( \
@@ -513,12 +554,22 @@ static inline notrace int ftrace_get_offsets_##call( \
__entry->__data_loc_##item = __data_offsets.item;

#undef __string
-#define __string(item, src) __dynamic_array(char, item, -1) \
+#define __string(item, src) __dynamic_array(char, item, -1)

#undef __assign_str
#define __assign_str(dst, src) \
strcpy(__get_str(dst), (src) ? (const char *)(src) : "(null)");

+#undef __cpumask
+#define __cpumask(item, src) __dynamic_array(unsigned long, item, -1)
+
+#undef __get_cpumask
+#define __get_cpumask(field) (char *)__get_dynamic_array(field)
+
+#undef __assign_cpumask
+#define __assign_cpumask(dst, src) \
+ memcpy(__get_cpumask(dst), (src), __cpumask_size_in_bytes)
+
#undef TP_fast_assign
#define TP_fast_assign(args...) args

@@ -586,6 +637,7 @@ static inline void ftrace_test_probe_##call(void) \
#undef __print_hex
#undef __get_dynamic_array
#undef __get_str
+#undef __get_cpumask

#undef TP_printk
#define TP_printk(fmt, args...) "\"" fmt "\", " __stringify(args)
@@ -651,6 +703,9 @@ __attribute__((section("_ftrace_events"))) *__event_##call = &event_##call
#undef __get_str
#define __get_str(field) (char *)__get_dynamic_array(field)

+#undef __get_cpumask
+#define __get_cpumask(field) (char *)__get_dynamic_array(field)
+
#undef __perf_addr
#define __perf_addr(a) (__addr = (a))

diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
index a436de1..de43631 100644
--- a/kernel/trace/trace_output.c
+++ b/kernel/trace/trace_output.c
@@ -126,6 +126,36 @@ trace_seq_printf(struct trace_seq *s, const char *fmt, ...)
EXPORT_SYMBOL_GPL(trace_seq_printf);

/**
+ * trace_seq_cpumask - put a list of longs as a cpumask print output
+ * @s: trace sequence descriptor
+ * @maskp: points to an array of unsigned longs that represent a cpumask
+ * @nmaskbits: The number of bits that are valid in @maskp
+ *
+ * It returns 0 if the trace oversizes the buffer's free
+ * space, 1 otherwise.
+ *
+ * Although the name has cpumask, it does not use the cpumask structure,
+ * but instead the internal bitmask structure used by cpumask. This
+ * is used for printing cpumasks in tracepoints.
+ */
+int
+trace_seq_cpumask(struct trace_seq *s, const unsigned long *maskp,
+ int nmaskbits)
+{
+ int len = (PAGE_SIZE - 1) - s->len;
+ int ret;
+
+ if (s->full || !len)
+ return 0;
+
+ ret = bitmap_scnprintf(s->buffer, len, maskp, nmaskbits);
+ s->len += ret;
+
+ return 1;
+}
+EXPORT_SYMBOL_GPL(trace_seq_cpumask);
+
+/**
* trace_seq_vprintf - sequence printing of trace information
* @s: trace sequence descriptor
* @fmt: printf format string
@@ -399,6 +429,19 @@ EXPORT_SYMBOL(ftrace_print_symbols_seq_u64);
#endif

const char *
+ftrace_print_cpumask_seq(struct trace_seq *p, void *cpumask_ptr,
+ unsigned int cpumask_size)
+{
+ const char *ret = p->buffer + p->len;
+
+ trace_seq_cpumask(p, cpumask_ptr, cpumask_size * 8);
+ trace_seq_putc(p, 0);
+
+ return ret;
+}
+EXPORT_SYMBOL_GPL(ftrace_print_cpumask_seq);
+
+const char *
ftrace_print_hex_seq(struct trace_seq *p, const unsigned char *buf, int buf_len)
{
int i;
--
1.8.1.4