perf/core, pt, bts: Get rid of itrace_started

I just noticed that hw.itrace_started and hw.config are aliased to the
same location. Now, the PT driver happens to use both, which works out
fine by sheer luck:

 - STORE(hw.itrace_start) is ordered before STORE(hw.config), in the
    program order, although there are no compiler barriers to ensure that,

 - to the perf_log_itrace_start() hw.itrace_start looks set at the same
   time as when it is intended to be set because both stores happen in the
   same path,

 - hw.config is never reset to zero in the PT driver.

Now, the use of hw.config by the PT driver makes more sense (it being a
HW PMU) than messing around with itrace_started, which is an awkward API
to begin with.

This patch replaces hw.itrace_started with an attach_state bit and an
API call for the PMU drivers to use to communicate the condition.

Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Arnaldo Carvalho de Melo <acme@infradead.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Cc: vince@deater.net
Link: http://lkml.kernel.org/r/20170330153956.25994-1-alexander.shishkin@linux.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

2 files changed, 4 insertions, 3 deletions

diff --git a/arch/x86/events/intel/bts.c b/arch/x86/events/intel/bts.c
index ddd8d3516bfc..16076eb34699 100644
--- a/arch/x86/events/intel/bts.c
+++ b/arch/x86/events/intel/bts.c
@@ -268,7 +268,7 @@ static void bts_event_start(struct perf_event *event, int flags)
 	bts->ds_back.bts_absolute_maximum = cpuc->ds->bts_absolute_maximum;
 	bts->ds_back.bts_interrupt_threshold = cpuc->ds->bts_interrupt_threshold;
 
-	event->hw.itrace_started = 1;
+	perf_event_itrace_started(event);
 	event->hw.state = 0;
 
 	__bts_event_start(event);
diff --git a/arch/x86/events/intel/pt.c b/arch/x86/events/intel/pt.c
index ae8324d65e61..81fd41d5a0d9 100644
--- a/arch/x86/events/intel/pt.c
+++ b/arch/x86/events/intel/pt.c
@@ -471,8 +471,9 @@ static void pt_config(struct perf_event *event)
 	struct pt *pt = this_cpu_ptr(&pt_ctx);
 	u64 reg;
 
-	if (!event->hw.itrace_started) {
-		event->hw.itrace_started = 1;
+	/* First round: clear STATUS, in particular the PSB byte counter. */
+	if (!event->hw.config) {
+		perf_event_itrace_started(event);
 		wrmsrl(MSR_IA32_RTIT_STATUS, 0);
 	}