Commit 571d91dc authored by Kan Liang's avatar Kan Liang Committed by Peter Zijlstra
Browse files

perf: Add branch stack counters 

Currently, the additional information of a branch entry is stored in a
u64 space. With more and more information added, the space is running
out. For example, the information of occurrences of events will be added
for each branch.

Two places were suggested to append the counters.
https://lore.kernel.org/lkml/20230802215814.GH231007@hirez.programming.kicks-ass.net/


One place is right after the flags of each branch entry. It changes the
existing struct perf_branch_entry. The later ARCH specific
implementation has to be really careful to consistently pick
the right struct.
The other place is right after the entire struct perf_branch_stack.
The disadvantage is that the pointer of the extra space has to be
recorded. The common interface perf_sample_save_brstack() has to be
updated.

The latter is much straightforward, and should be easily understood and
maintained. It is implemented in the patch.

Add a new branch sample type, PERF_SAMPLE_BRANCH_COUNTERS, to indicate
the event which is recorded in the branch info.

The "u64 counters" may store the occurrences of several events. The
information regarding the number of events/counters and the width of
each counter should be exposed via sysfs as a reference for the perf
tool. Define the branch_counter_nr and branch_counter_width ABI here.
The support will be implemented later in the Intel-specific patch.

Suggested-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: default avatarKan Liang <kan.liang@linux.intel.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20231025201626.3000228-1-kan.liang@linux.intel.com
parent 744940f1

Documentation/ABI/testing/sysfs-bus-event_source-devices-caps

+6 −0
Original line number Diff line number Diff line
@@ -16,3 +16,9 @@ Description: 
		Example output in powerpc:

		grep . /sys/bus/event_source/devices/cpu/caps/*

		/sys/bus/event_source/devices/cpu/caps/pmu_name:POWER9



		The "branch_counter_nr" in the supported platform exposes the

		maximum number of counters which can be shown in the u64 counters

		of PERF_SAMPLE_BRANCH_COUNTERS, while the "branch_counter_width"

		exposes the width of each counter. Both of them can be used by

		the perf tool to parse the logged counters in each branch.

arch/powerpc/perf/core-book3s.c

+1 −1
Original line number Diff line number Diff line
@@ -2313,7 +2313,7 @@ static void record_and_restart(struct perf_event *event, unsigned long val, 
			struct cpu_hw_events *cpuhw;

			cpuhw = this_cpu_ptr(&cpu_hw_events);

			power_pmu_bhrb_read(event, cpuhw);

			perf_sample_save_brstack(&data, event, &cpuhw->bhrb_stack);

			perf_sample_save_brstack(&data, event, &cpuhw->bhrb_stack, NULL);

		}



		if (event->attr.sample_type & PERF_SAMPLE_DATA_SRC &&

arch/x86/events/amd/core.c

+1 −1
Original line number Diff line number Diff line
@@ -940,7 +940,7 @@ static int amd_pmu_v2_handle_irq(struct pt_regs *regs) 
			continue;



		if (has_branch_stack(event))

			perf_sample_save_brstack(&data, event, &cpuc->lbr_stack);

			perf_sample_save_brstack(&data, event, &cpuc->lbr_stack, NULL);



		if (perf_event_overflow(event, &data, regs))

			x86_pmu_stop(event, 0);

arch/x86/events/core.c

+1 −1
Original line number Diff line number Diff line
@@ -1702,7 +1702,7 @@ int x86_pmu_handle_irq(struct pt_regs *regs) 
		perf_sample_data_init(&data, 0, event->hw.last_period);



		if (has_branch_stack(event))

			perf_sample_save_brstack(&data, event, &cpuc->lbr_stack);

			perf_sample_save_brstack(&data, event, &cpuc->lbr_stack, NULL);



		if (perf_event_overflow(event, &data, regs))

			x86_pmu_stop(event, 0);

arch/x86/events/intel/core.c

+1 −1
Original line number Diff line number Diff line
@@ -3047,7 +3047,7 @@ static int handle_pmi_common(struct pt_regs *regs, u64 status) 
		perf_sample_data_init(&data, 0, event->hw.last_period);



		if (has_branch_stack(event))

			perf_sample_save_brstack(&data, event, &cpuc->lbr_stack);

			perf_sample_save_brstack(&data, event, &cpuc->lbr_stack, NULL);



		if (perf_event_overflow(event, &data, regs))

			x86_pmu_stop(event, 0);