[PATCH v8 11/11] KVM: selftests: Cache binary stats metadata for duration of test

[Ben Gardon <bgardon@xxxxxxxxxx>]

In order to improve performance across multiple reads of VM stats, cache
the stats metadata in the VM struct.

Signed-off-by: Ben Gardon <bgardon@xxxxxxxxxx>
---
 tools/testing/selftests/kvm/lib/kvm_util.c    | 32 ++++++++++---------
 .../selftests/kvm/lib/kvm_util_internal.h     |  5 +++
 2 files changed, 22 insertions(+), 15 deletions(-)

diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c
index 33d4d64c1391..a32b7b4352b9 100644
--- a/tools/testing/selftests/kvm/lib/kvm_util.c
+++ b/tools/testing/selftests/kvm/lib/kvm_util.c
@@ -736,6 +736,12 @@ void kvm_vm_free(struct kvm_vm *vmp)
 	if (vmp == NULL)
 		return;
 
+	/* Free cached stats metadata and close FD */
+	if (vmp->stats_fd) {
+		free(vmp->stats_desc);
+		close(vmp->stats_fd);
+	}
+
 	/* Free userspace_mem_regions. */
 	hash_for_each_safe(vmp->regions.slot_hash, ctr, node, region, slot_node)
 		__vm_mem_region_delete(vmp, region, false);
@@ -2694,34 +2700,30 @@ void read_stat_data(int stats_fd, struct kvm_stats_header *header,
 void __vm_get_stat(struct kvm_vm *vm, const char *stat_name, uint64_t *data,
 		   size_t max_elements)
 {
-	struct kvm_stats_desc *stats_desc;
-	struct kvm_stats_header header;
 	struct kvm_stats_desc *desc;
 	size_t size_desc;
-	int stats_fd;
 	int i;
 
-	stats_fd = vm_get_stats_fd(vm);
-
-	read_stats_header(stats_fd, &header);
-
-	stats_desc = read_stats_descriptors(stats_fd, &header);
+	if (!vm->stats_fd) {
+		vm->stats_fd = vm_get_stats_fd(vm);
+		read_stats_header(vm->stats_fd, &vm->stats_header);
+		vm->stats_desc = read_stats_descriptors(vm->stats_fd,
+							&vm->stats_header);
+	}
 
-	size_desc = get_stats_descriptor_size(&header);
+	size_desc = get_stats_descriptor_size(&vm->stats_header);
 
-	for (i = 0; i < header.num_desc; ++i) {
-		desc = (void *)stats_desc + (i * size_desc);
+	for (i = 0; i < vm->stats_header.num_desc; ++i) {
+		desc = (void *)vm->stats_desc + (i * size_desc);
 
 		if (strcmp(desc->name, stat_name))
 			continue;
 
-		read_stat_data(stats_fd, &header, desc, data, max_elements);
+		read_stat_data(vm->stats_fd, &vm->stats_header, desc,
+			       data, max_elements);
 
 		break;
 	}
-
-	free(stats_desc);
-	close(stats_fd);
 }
 
 /* VM disable NX huge pages
diff --git a/tools/testing/selftests/kvm/lib/kvm_util_internal.h b/tools/testing/selftests/kvm/lib/kvm_util_internal.h
index a03febc24ba6..e753edd7b8d3 100644
--- a/tools/testing/selftests/kvm/lib/kvm_util_internal.h
+++ b/tools/testing/selftests/kvm/lib/kvm_util_internal.h
@@ -67,6 +67,11 @@ struct kvm_vm {
 	vm_vaddr_t idt;
 	vm_vaddr_t handlers;
 	uint32_t dirty_ring_size;
+
+	/* Cache of information for binary stats interface */
+	int stats_fd;
+	struct kvm_stats_header stats_header;
+	struct kvm_stats_desc *stats_desc;
 };
 
 struct vcpu *vcpu_find(struct kvm_vm *vm, uint32_t vcpuid);
-- 
2.36.1.124.g0e6072fb45-goog