linux-kernel - [PATCH] perf, x86: Don't use clock function pointer to determine clock

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Date:	Thu, 14 Apr 2016 14:59:49 +0300
From:	Alexander Shishkin <alexander.shishkin@...ux.intel.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	vince@...ter.net, eranian@...gle.com,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Borislav Petkov <bp@...en8.de>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Daniel Lezcano <daniel.lezcano@...aro.org>
Subject: [PATCH] perf, x86: Don't use clock function pointer to determine clock

Now that local_clock() is explicitly inlined in sched.h, taking its
pointer would uninline it in the compilation unit where it's done,
making (among other things) comparing pointers to this function
produce different results in different compilation units.

Case in point, x86 perf core's user page updating function compares
event's clock against &local_clock to see if it needs to set zero
time offset related bits in the page.

This patch fixes the latter by looking at the "use_clockid" event
attribute instead, to determine whether local clock is used. Fixing
the uninlined local_clock() in perf core is left as an exercise for
the author of the prior work.

Cc: Daniel Lezcano <daniel.lezcano@...aro.org>
Fixes: http://lkml.kernel.org/r/1459541050-13654-1-git-send-email-daniel.lezcano@linaro.org
Signed-off-by: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
---
 arch/x86/events/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
index 002b2eadd6..945ce189f5 100644
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -2177,7 +2177,7 @@ void arch_perf_update_userpage(struct perf_event *event,
 	 * cap_user_time_zero doesn't make sense when we're using a different
 	 * time base for the records.
 	 */
-	if (event->clock == &local_clock) {
+	if (!event->attr.use_clockid) {
 		userpg->cap_user_time_zero = 1;
 		userpg->time_zero = data->cyc2ns_offset;
 	}
-- 
2.8.0.rc3