Re: [PATCH v3 2/3] tracing: Add trace_irqsoff tracepoints

From: Daniel Wagner
Date: Tue Aug 30 2016 - 11:02:22 EST


On 08/30/2016 04:20 PM, Daniel Wagner wrote:
> Just setting the size of the type is not enough. The hist_field_*
> getter function want to know the offset too:

With this hack here it should work. The COMM generic field is handled via
the tracing_map_ops. We could do it also there but than we need to
a condition in the trace_map_ops if it is COMM or CPU.
This shortcut here avoids it:

diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 03c0a48..ab8958f 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -152,7 +152,8 @@ EXPORT_SYMBOL_GPL(trace_define_field);

#define __generic_field(type, item, filter_type) \
ret = __trace_define_field(&ftrace_generic_fields, #type, \
- #item, 0, 0, is_signed_type(type), \
+ #item, 0, sizeof(type), \
+ is_signed_type(type), \
filter_type); \
if (ret) \
return ret;
diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index f3a960e..77073b7 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -75,6 +75,11 @@ static u64 hist_field_log2(struct hist_field *hist_field, void *event)
return (u64) ilog2(roundup_pow_of_two(val));
}

+static u64 hist_field_cpu(struct hist_field *hist_field, void *event)
+{
+ return (u64) smp_processor_id();
+}
+
#define DEFINE_HIST_FIELD_FN(type) \
static u64 hist_field_##type(struct hist_field *hist_field, void *event)\
{ \
@@ -119,6 +124,7 @@ enum hist_field_flags {
HIST_FIELD_FL_SYSCALL = 128,
HIST_FIELD_FL_STACKTRACE = 256,
HIST_FIELD_FL_LOG2 = 512,
+ HIST_FIELD_FL_CPU = 1024,
};

struct hist_trigger_attrs {
@@ -371,6 +377,11 @@ static struct hist_field *create_hist_field(struct ftrace_event_field *field,
goto out;
}

+ if (flags & HIST_FIELD_FL_CPU) {
+ hist_field->fn = hist_field_cpu;
+ goto out;
+ }
+
if (WARN_ON_ONCE(!field))
goto out;

@@ -556,6 +567,11 @@ static int create_key_field(struct hist_trigger_data *hist_data,
key_size = MAX_FILTER_STR_VAL;
else
key_size = field->size;
+
+ // strcmp(field_name, "cpu") would also work to figure
+ // out if this is a one of the generic fields.
+ if (field->filter_type == FILTER_CPU)
+ flags |= HIST_FIELD_FL_CPU;
}

hist_data->fields[key_idx] = create_hist_field(field, flags);