Re: [PATCH V2 0/6] perf: New conditional branch filter

On Mon, 2013-09-23 at 14:45 +0530, Anshuman Khandual wrote:

On 09/21/2013 12:25 PM, Stephane Eranian wrote:

quoted

On Tue, Sep 10, 2013 at 4:06 AM, Michael Ellerman
[off-list ref] wrote:

quoted

quoted

On Fri, 2013-08-30 at 09:54 +0530, Anshuman Khandual wrote:

quoted

quoted

      This patchset is the re-spin of the original branch stack sampling
patchset which introduced new PERF_SAMPLE_BRANCH_COND filter. This patchset
also enables SW based branch filtering support for PPC64 platforms which have
branch stack sampling support. With this new enablement, the branch filter support
for PPC64 platforms have been extended to include all these combinations discussed
below with a sample test application program.

...

quoted

quoted

Mixed filters
-------------
(6) perf record -e branch-misses:u -j any_call,any_ret ./cprog
Error:
The perf.data file has no samples!

NOTE: As expected. The HW filters all the branches which are calls and SW tries to find return
branches in that given set. Both the filters are mutually exclussive, so obviously no samples
found in the end profile.

The semantics of multiple filters is not clear to me. It could be an OR,
or an AND. You have implemented AND, does that match existing behaviour
on x86 for example?

The semantic on the API is OR. AND does not make sense: CALL & RETURN?
On x86, the HW filter is an OR (default: ALL, set bit to disable a
type). I suspect
it is similar on PPC.

Given the situation as explained here, which semantic would be better for single
HW and multiple SW filters. Accordingly validate_instruction() function will have
to be re-implemented. But I believe OR-ing the SW filters will be preferable.

	(1) (HW_FILTER_1) && (SW_FILTER_1) && (SW_FILTER_2)
	or
	(2) (HW_FILTER_1) && (SW_FILTER_1 || SW_FILTER_2)

Please let me know your inputs and suggestions on this. Thank you.

You need to implement the correct semantics, regardless of how the
hardware happens to work.

That means if multiple filters are specified you need to do all the
filtering in software.

cheers