It is all well described by Stephen Rothwell who initially spotted that:
----------------------------->8----------------------------
After merging the origin tree, today's linux-next build (arc
haps_hs_smp_defconfig+kselftest) produced these warnings:

arch/arc/include/asm/perf_event.h:126:27: warning: 'arc_pmu_cache_map' defined but not used [-Wunused-const-variable=]
arch/arc/include/asm/perf_event.h:91:27: warning: 'arc_pmu_ev_hw_map' defined but not used [-Wunused-const-variable=]

Introduced by commit 0dd450fe ("ARC: Add perf support for ARC700 cores")

The 2 static arrays should be moved into arch/arc/kernel/perf_event.c
(the only place that uses them). We get the warning because perf_event.h
is also included by arch/arc/kernel/unaligned.c.
----------------------------->8----------------------------

Could be easily reproduced by running make with "W=1" on any up-to-date
sources, when extra warnings get enabled (in particular
"-Wunused-const-variable"), otherwise disabled by default in the top-level
Makefile as "These warnings generated too much noise in a regular build".

Cc: Mischa Jonker <mjonker@synopsys.com>
Reported-by: NStephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: NAlexey Brodkin <abrodkin@synopsys.com>
Signed-off-by: NVineet Gupta <vgupta@kernel.org>