Re: [PATCH v2 2/2] perf: Userspace event

On Thu, 25 Sep 2014 13:45:05 +0100, Pawel Moll wrote:

On Wed, 2014-09-24 at 07:07 +0100, Namhyung Kim wrote:

quoted

On Tue, 23 Sep 2014 18:03:07 +0100, Pawel Moll wrote:

quoted

This patch adds a new PERF_COUNT_SW_UEVENT software event
and a related PERF_SAMPLE_UEVENT sample. User can now
write to the the perf file descriptor, injecting such
event in the perf buffer.

It seems the PERF_SAMPLE_UEVENT sample can be injected to any event.  So
why the PERF_COUNT_SW_UEVENT is needed?  At least one can use the
SW_DUMMY event for that purpose.

You're right. I needed a different SW type in one of my early
prototypes, but it's not the case any more. Consider it gone.

Okay.

quoted

Also I think it'd be better to be a record type (PERF_RECORD_XXX)
instead of a sample flag (PERF_SAMPLE_XXX).  In perf tools, we already
use perf_user_event_type for synthesized userspace events.  This way it
can avoid unnecessary sample processing for userspace events.

Fine with me. If no one objects, I'm more than happy to use
PERF_RECORD_UEVENT = 11 for it.

quoted

For contents, I prefer to give complete control to users - kernel
doesn't need to care about it other than its size.  If one just wants to
use strings only, she can write them directly.  If others want to mix
different types of data, they might need to define a data format for
their use.

Are you saying to drop even the "type 0 means zero-terminated string"
definition, even if everything else is up to the user? I quite like that
idea, especially combined with write()ing to the perf_fd (it is very
much like trace_marker then, which is beautiful in its simplicity), but
the feelings are not that strong to fight a war over it.

:)


Thanks,
Namhyung