linux-kernel - [PATCH 5/5] arm64: perf: Add cap_user_time

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Date:   Tue, 12 May 2020 14:41:03 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Will Deacon <will@...nel.org>, Marc Zyngier <maz@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Leo Yan <leo.yan@...aro.org>
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        mingo@...hat.com, acme@...nel.org,
        alexander.shishkin@...ux.intel.com, jolsa@...hat.com,
        daniel.lezcano@...aro.org, tglx@...utronix.de,
        sboyd@...eaurora.org, john.stultz@...aro.org,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>
Subject: [PATCH 5/5] arm64: perf: Add cap_user_time_short

This completes the ARM64 cap_user_time support.

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

--- a/arch/arm64/kernel/perf_event.c
+++ b/arch/arm64/kernel/perf_event.c
@@ -1173,6 +1173,7 @@ void arch_perf_update_userpage(struct pe
 
 	userpg->cap_user_time = 0;
 	userpg->cap_user_time_zero = 0;
+	userpg->cap_user_time_short = 0;
 
 	do {
 		rd = sched_clock_read_begin(&seq);
@@ -1183,13 +1184,13 @@ void arch_perf_update_userpage(struct pe
 		userpg->time_mult = rd->mult;
 		userpg->time_shift = rd->shift;
 		userpg->time_zero = rd->epoch_ns;
+		userpg->time_cycle = 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.
 		 */
 		userpg->time_zero -= (rd->epoch_cyc * rd->mult) >> rd->shift;
 
@@ -1214,4 +1215,5 @@ void arch_perf_update_userpage(struct pe
 	 */
 	userpg->cap_user_time = 1;
 	userpg->cap_user_time_zero = 1;
+	userpg->cap_user_time_short = 1;
 }