[PATCH v2 5/6] arm64: perf: Add cap_user_time_short

[Leo Yan]

From: Peter Zijlstra <peterz at infradead.org>

This completes the ARM64 cap_user_time support.

Signed-off-by: Peter Zijlstra (Intel) <peterz at infradead.org>
---
 arch/arm64/kernel/perf_event.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/kernel/perf_event.c b/arch/arm64/kernel/perf_event.c
index 76f6afd28b48..1e0f15305f67 100644
--- a/arch/arm64/kernel/perf_event.c
+++ b/arch/arm64/kernel/perf_event.c
@@ -1174,6 +1174,7 @@ void arch_perf_update_userpage(struct perf_event *event,
 
 	userpg->cap_user_time = 0;
 	userpg->cap_user_time_zero = 0;
+	userpg->cap_user_time_short = 0;
 
 	do {
 		rd = sched_clock_read_begin(&seq);
@@ -1184,13 +1185,13 @@ void arch_perf_update_userpage(struct perf_event *event,
 		userpg->time_mult = rd->mult;
 		userpg->time_shift = rd->shift;
 		userpg->time_zero = rd->epoch_ns;
+		userpg->time_cycles = rd->epoch_cyc;
+		userpg->time_mask = rd->sched_clock_mask;
 
 		/*
-		 * This isn't strictly correct, the ARM64 counter can be
-		 * 'short' and then we get funnies when it wraps. The correct
-		 * thing would be to extend the perf ABI with a cycle and mask
-		 * value, but because wrapping on ARM64 is very rare in
-		 * practise this 'works'.
+		 * Subtract the cycle base, such that software that
+		 * doesn't know about cap_user_time_short still 'works'
+		 * assuming no wraps.
 		 */
 		quot = rd->epoch_cyc >> rd->shift;
 		rem = rd->epoch_cyc & (((u64)1 << rd->shift) - 1);
@@ -1218,4 +1219,5 @@ void arch_perf_update_userpage(struct perf_event *event,
 	 */
 	userpg->cap_user_time = 1;
 	userpg->cap_user_time_zero = 1;
+	userpg->cap_user_time_short = 1;
 }
-- 
2.17.1