On Fri, 11 Aug 2017, Mark Rutland wrote:

> IIRC, patches were sent back in 2014, but as I mentioned above, those
> were far from suitable for upstream, even ignoring cases like
> big.LITTLE. Said patches were never reworked and reposted.

Here's the commit message in the perf_event_tests tree, having trouble 
finding the original e-mail that went with it.

commit 2cc2e21e349243889ba59408527cc1a97dd0dc44
Author: Yogesh Tillu <yogesh.ti...@linaro.org>
Date:   Tue Mar 1 14:18:22 2016 +0530

    Add support for RDPMC test with mmap way
    This test adds support for reading perf hw counter from userspace.
    Method (2)
    Test read perf hw counter in userspace using open/mmap syscall.
    It requires kernel with perf mmap patchset and
    echo 1 > /sys/bus/platform/drivers/armv8-pmu/rdpmc
    Above Method Tested On:(X86/ARM)
    It is tested with perf mmap patchset on kernel v4.5.0-rc5+
    With above Tests, we can benchmark access of perf hw counters in
    userspace with syscall vs perf_event_mmap_page way.
    Signed-off-by: Yogesh Tillu <yogesh.ti...@linaro.org>

> Just to check, how does x86 behave on each of those kernel releases?
> Many things have changed since v4.4.

I'm fairly sure this test (well, the equivelent code in 
tests/record_sample/record_mmap that I based the test on) has been passing 
on all of my x86 test machines since ~3.10 or so, or else I would noticed.

If I can get a custom kernel to boot on one of my machines I can start 
digging in and see if I can find where the EINVAL comes from.

This isn't some key thing that needs to be fixed, I was just curious about 
the behavior difference between x86 and ARM.  There are a few other minor 
x86/ARM diferences, especially realting to perf_event_open() error 
returns, that I had to special case in a few of my tests.


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