arm64: perf: Implement correct cap_user_time

As reported by Leo; the existing implementation is broken when the
clock and counter don't intersect at 0.

Use the sched_clock's struct clock_read_data information to correctly
implement cap_user_time and cap_user_time_zero.

Note that the ARM64 counter is architecturally only guaranteed to be
56bit wide (implementations are allowed to be wider) and the existing
perf ABI cannot deal with wrap-around.

This implementation should also be faster than the old; seeing how we
don't need to recompute mult and shift all the time.

[leoyan: Use mul_u64_u32_shr() to convert cyc to ns to avoid overflow]

Reported-by: Leo Yan <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Leo Yan <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Will Deacon <[email protected]>

0 files changed, 0 insertions, 0 deletions