Commit ba9786f3 authored by Deng-Cheng Zhu's avatar Deng-Cheng Zhu Committed by Ralf Baechle

MIPS, Perf-events: Use unsigned delta for right shift in event update

Leverage the commit for ARM by Will Deacon:

- 446a5a8b
    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.
Acked-by: default avatarWill Deacon <will.deacon@arm.com>
Acked-by: default avatarDavid Daney <ddaney@caviumnetworks.com>
Signed-off-by: default avatarDeng-Cheng Zhu <dengcheng.zhu@gmail.com>
To: a.p.zijlstra@chello.nl
To: fweisbec@gmail.com
To: will.deacon@arm.com
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Cc: wuzhangjin@gmail.com
Cc: paulus@samba.org
Cc: mingo@elte.hu
Cc: acme@redhat.com
Cc: matt@console-pimps.org
Cc: sshtylyov@mvista.com
Patchwork: http://patchwork.linux-mips.org/patch/2015/Signed-off-by: default avatarRalf Baechle <ralf@linux-mips.org>
parent 98f92f2f
...@@ -169,7 +169,7 @@ static void mipspmu_event_update(struct perf_event *event, ...@@ -169,7 +169,7 @@ static void mipspmu_event_update(struct perf_event *event,
unsigned long flags; unsigned long flags;
int shift = 64 - TOTAL_BITS; int shift = 64 - TOTAL_BITS;
s64 prev_raw_count, new_raw_count; s64 prev_raw_count, new_raw_count;
s64 delta; u64 delta;
again: again:
prev_raw_count = local64_read(&hwc->prev_count); prev_raw_count = local64_read(&hwc->prev_count);
......
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