perf kvm: Use subtraction for comparison metrics

Currently the metrics comparison uses greater operator (>), it returns
the boolean value (0 or 1).

This patch changes to use subtraction as comparison result, which can
be used by histograms sorting.  Since the subtraction result is u64
type, we change key_cmp_fun's return type to int64_t to avoid overflow.
Signed-off-by: Leo Yan <leo.yan@linaro.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Clark <james.clark@arm.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: John Garry <john.g.garry@oracle.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: linux-arm-kernel@lists.infradead.org
Link: https://lore.kernel.org/r/20230315145112.186603-2-leo.yan@linaro.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-kvm.c

@@ -64,10 +64,10 @@ static u64 get_event_ ##func(struct kvm_event *event, int vcpu)		\
 
 #define COMPARE_EVENT_KEY(func, field)					\
 GET_EVENT_KEY(func, field)						\
-static int cmp_event_ ## func(struct kvm_event *one,			\
+static int64_t cmp_event_ ## func(struct kvm_event *one,		\
 			      struct kvm_event *two, int vcpu)		\
 {									\
-	return get_event_ ##func(one, vcpu) >				\
+	return get_event_ ##func(one, vcpu) -				\
 	       get_event_ ##func(two, vcpu);				\
 }
 
@@ -525,7 +525,7 @@ static void insert_to_result(struct rb_root *result, struct kvm_event *event,
 		p = container_of(*rb, struct kvm_event, rb);
 		parent = *rb;
 
-		if (bigger(event, p, vcpu))
+		if (bigger(event, p, vcpu) > 0)
 			rb = &(*rb)->rb_left;
 		else
 			rb = &(*rb)->rb_right;

tools/perf/util/kvm-stat.h

@@ -40,7 +40,7 @@ struct kvm_event {
 	struct kvm_event_stats *vcpu;
 };
 
-typedef int (*key_cmp_fun)(struct kvm_event*, struct kvm_event*, int);
+typedef int64_t (*key_cmp_fun)(struct kvm_event*, struct kvm_event*, int);
 
 struct kvm_event_key {
 	const char *name;