ARM: 6205/1: perf: ensure counter delta is treated as unsigned
authorWill Deacon <will.deacon@arm.com>
Fri, 2 Jul 2010 15:41:52 +0000 (16:41 +0100)
committerRussell King <rmk+kernel@arm.linux.org.uk>
Sun, 4 Jul 2010 22:11:37 +0000 (23:11 +0100)
commit446a5a8b1eb91a6990e5c8fe29f14e7a95b69132
treedd60d5a5db4438d66e0baa78acda85f7be4fbae6
parent42c4dafe803dcad82980fd8b0831a89032156f93
ARM: 6205/1: perf: ensure counter delta is treated as unsigned

Hardware performance counters on ARM are 32-bits wide but atomic64_t
variables are used to represent counter data in the hw_perf_event structure.

The armpmu_event_update function right-shifts a signed 64-bit delta variable
and adds the result to the event count. This can lead to shifting in sign-bits
if the MSB of the 32-bit counter value is set. This results in perf output
such as:

 Performance counter stats for 'sleep 20':

 18446744073460670464  cycles             <-- 0xFFFFFFFFF12A6000
        7783773  instructions             #      0.000 IPC
            465  context-switches
            161  page-faults
        1172393  branches

   20.154242147  seconds time elapsed

This patch ensures that the delta value is treated as unsigned so that the
right shift sets the upper bits to zero.

Cc: <stable@kernel.org>
Acked-by: Jamie Iles <jamie.iles@picochip.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
arch/arm/kernel/perf_event.c