On 05/22/2014 10:22 AM, Peter Zijlstra wrote:
> On Thu, May 22, 2014 at 09:52:46AM +0300, Adrian Hunter wrote:
>> +/*
>> + * PERF_RECORD_MISC_MMAP_DATA and PERF_RECORD_MISC_COMM_EXEC are used on
>> + * different events so can reuse the same bit position.
>> + */
>> #define PERF_RECORD_MISC_MMAP_DATA (1 << 13)
>> +#define PERF_RECORD_MISC_COMM_EXEC (1 << 13)
>> /*
>> * Indicates that the content of PERF_SAMPLE_IP points to
>> * the actual instruction that triggered the event. See also
>> diff --git a/kernel/events/core.c b/kernel/events/core.c
>> index ed50b09..760abd0 100644
>> --- a/kernel/events/core.c
>> +++ b/kernel/events/core.c
>> @@ -5067,7 +5067,7 @@ static void perf_event_comm_event(struct
>> perf_comm_event *comm_event)
>> NULL);
>> }
>>
>> -void perf_event_comm(struct task_struct *task)
>> +void perf_event_comm(struct task_struct *task, bool exec)
>> {
>> struct perf_comm_event comm_event;
>> struct perf_event_context *ctx;
>> @@ -5093,7 +5093,7 @@ void perf_event_comm(struct task_struct *task)
>> .event_id = {
>> .header = {
>> .type = PERF_RECORD_COMM,
>> - .misc = 0,
>> + .misc = exec ? PERF_RECORD_MISC_COMM_EXEC : 0,
>> /* .size */
>> },
>> /* .pid */
>
> OK, now that you pointed out the obvious, yeah, I suppose we can do that :-)
>
One problem is how user space can figure out if the kernel supports it.
For my purposes, I don't need to know in advance, but I can imagine some
users might want to. So I suggest adding:
diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
index e3fc8f0..67cec3e 100644
--- a/include/uapi/linux/perf_event.h
+++ b/include/uapi/linux/perf_event.h
@@ -301,8 +301,9 @@ struct perf_event_attr {
exclude_callchain_kernel : 1, /* exclude kernel
callchains */
exclude_callchain_user : 1, /* exclude user
callchains */
mmap2 : 1, /* include mmap with inode
data */
+ exec : 1, /* flag comm events that
are due to an exec */
- __reserved_1 : 40;
+ __reserved_1 : 39;
union {
__u32 wakeup_events; /* wakeup every n events */
Commit message:
perf tools like 'perf report' can aggregate samples by comm
strings, which generally works. However, there are other
potential use-cases. For example, to pair up 'calls'
with 'returns' accurately (from branch events like Intel BTS)
it is necessary to identify whether the process has exec'd.
Although a comm event is generated when an 'exec' happens
it is also generated whenever the comm string is changed
on a whim (e.g. by prctl PR_SET_NAME). This patch adds a
flag to the comm event to differentiate one case from the
other.
In order to determine whether the kernel supports the new
flag, a selection bit named 'exec' is added to struct
perf_event_attr. The bit does nothing but will cause
perf_event_open() to fail if the bit is set on kernels
that do not have it defined.
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