On Fri, Apr 30, 2021 at 1:59 PM Arnaldo Carvalho de Melo
[off-list ref] wrote:

Em Mon, Apr 19, 2021 at 10:15:02PM -0500, Rob Herring escreveu:

quoted

Hi all,

Another version of arm64 userspace counter access support. I sent out
the libperf bits separately and those are now applied (Thanks!), so this
is just the arm64 bits.


This originally resurrected Raphael's series[1] to enable userspace counter
access on arm64. My previous versions are here[2][3][4][5][6][7]. A git
branch is here[8].

Rob, please don't mix kernel patches with tools patches. The kernel
bits, if arch specific should go via the arch maintainer, core stuff to
PeterZ/Ingo/bpetkov/tglx, and tooling stuff I'll collect.

Okay, perhaps MAINTAINERS should be updated to reflect that better.

We did it on purpose to avoid any semblance of kernel/tool lockstep.

The kernel changes should not prevent the tooling from working and the
tooling changes shouldn't require the kernel changes.

Preexisting kernels should work with new tools and vice versa.

The only issue I see here is the userspace access tests will fail if
enabled in libperf for an arch but run on an older kernel without
userspace access support. I could instead skip tests if cap_user_rdpmc
is not set, but then how to test that it is set when it should be? I
suppose checking sysfs 'rdpmc' is one option assuming we end up with
the same file on Arm.

Rob

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