Commit 8d4e6c4c authored by Alexander Shishkin's avatar Alexander Shishkin Committed by Ingo Molnar
Browse files

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: default avatarAlexander Shishkin <alexander.shishkin@linux.intel.com>
Signed-off-by: default avatarPeter 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: default avatarIngo Molnar <mingo@kernel.org>
parent e0563e04

arch/x86/events/intel/bts.c

+1 −1
Original line number Diff line number Diff line
@@ -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);

arch/x86/events/intel/pt.c

+3 −2
Original line number Diff line number Diff line
@@ -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);

	}

include/linux/perf_event.h

+2 −3
Original line number Diff line number Diff line
@@ -147,9 +147,6 @@ struct hw_perf_event { 
			struct list_head	cqm_groups_entry;

			struct list_head	cqm_group_entry;

		};

		struct { /* itrace */

			int			itrace_started;

		};

		struct { /* amd_power */

			u64	pwr_acc;

			u64	ptsc;
@@ -541,6 +538,7 @@ struct swevent_hlist { 
#define PERF_ATTACH_GROUP	0x02

#define PERF_ATTACH_TASK	0x04

#define PERF_ATTACH_TASK_DATA	0x08

#define PERF_ATTACH_ITRACE	0x10



struct perf_cgroup;

struct ring_buffer;
@@ -864,6 +862,7 @@ extern int perf_aux_output_skip(struct perf_output_handle *handle, 
				unsigned long size);

extern void *perf_get_aux(struct perf_output_handle *handle);

extern void perf_aux_output_flag(struct perf_output_handle *handle, u64 flags);

extern void perf_event_itrace_started(struct perf_event *event);



extern int perf_pmu_register(struct pmu *pmu, const char *name, int type);

extern void perf_pmu_unregister(struct pmu *pmu);

kernel/events/core.c

+6 −1
Original line number Diff line number Diff line
@@ -7301,6 +7301,11 @@ static void perf_log_throttle(struct perf_event *event, int enable) 
	perf_output_end(&handle);

}



void perf_event_itrace_started(struct perf_event *event)

{

	event->attach_state |= PERF_ATTACH_ITRACE;

}



static void perf_log_itrace_start(struct perf_event *event)

{

	struct perf_output_handle handle;
@@ -7316,7 +7321,7 @@ static void perf_log_itrace_start(struct perf_event *event) 
		event = event->parent;



	if (!(event->pmu->capabilities & PERF_PMU_CAP_ITRACE) ||

	    event->hw.itrace_started)

	    event->attach_state & PERF_ATTACH_ITRACE)

		return;



	rec.header.type	= PERF_RECORD_ITRACE_START;

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