Re: [PATCH v21 4/4] perf: arm_pmuv3: Add support for the Branch Record Buffer Extension (BRBE)

On Wed, May 21, 2025 at 04:58:42PM +0100, James Clark wrote:

On 19/05/2025 10:56 pm, Rob Herring wrote:

quoted

On Mon, May 19, 2025 at 04:06:22PM +0100, Will Deacon wrote:

quoted

Hey Rob,

On Mon, Apr 07, 2025 at 12:41:33PM -0500, Rob Herring (Arm) wrote:

quoted

From: Anshuman Khandual <redacted>

The ARMv9.2 architecture introduces the optional Branch Record Buffer
Extension (BRBE), which records information about branches as they are
executed into set of branch record registers. BRBE is similar to x86's
Last Branch Record (LBR) and PowerPC's Branch History Rolling Buffer
(BHRB).

Since you picked this up from v19, the driver has changed considerably
and I presume you will be continuing to extend it in future as the
architecture progresses. Perhaps having you listed as Author (and
crucially, in git blame :p) with Anshuman as a Co-developed-by: would be
more appropriate?

Shrug.

quoted

quoted

---
  drivers/perf/Kconfig         |  11 +
  drivers/perf/Makefile        |   1 +
  drivers/perf/arm_brbe.c      | 802 +++++++++++++++++++++++++++++++++++++++++++
  drivers/perf/arm_brbe.h      |  47 +++
  drivers/perf/arm_pmu.c       |  15 +-
  drivers/perf/arm_pmuv3.c     | 129 ++++++-
  include/linux/perf/arm_pmu.h |   8 +
  7 files changed, 1006 insertions(+), 7 deletions(-)

Do you know if James Clark's tests [1] are going to be respun for the
perf tool? It would be handy to have some way to test this new
functionality.

Yes. I dropped them here because I've been told by Arnaldo in the past
to send userspace stuff separately.

That version of the test was out of date so I've pushed the new version
here: https://git.linaro.org/plugins/gitiles/people/james.clark/linux.git/+/16e4a18c2d5fc53736f05c9052b1d11d74909707

But I'll wait for the driver changes to be finalised before posting it. Or
Rob can take it back into the patchset.

Thanks, James. I just wanted to make sure that there was still a plan
for upstreaming these separately from the driver. Have you had a chance
to run them against this v21?

Will