Re: [PATCH 3/6] KVM: selftests: memslot_perf_test: Probe memory slots for once

From: Maciej S. Szmigiero
Date: Mon Oct 17 2022 - 13:35:23 EST


On 14.10.2022 09:19, Gavin Shan wrote:
prepare_vm() is called in every iteration and run. The allowed memory
slots (KVM_CAP_NR_MEMSLOTS) are probed for multiple times. It's not
free and unnecessary.

Move the probing logic for the allowed memory slots to parse_args()
for once, which is upper layer of prepare_vm().

No functional change intended.

Signed-off-by: Gavin Shan <gshan@xxxxxxxxxx>
---
.../testing/selftests/kvm/memslot_perf_test.c | 29 ++++++++++---------
1 file changed, 16 insertions(+), 13 deletions(-)

diff --git a/tools/testing/selftests/kvm/memslot_perf_test.c b/tools/testing/selftests/kvm/memslot_perf_test.c
index dcb492b3f27b..d5aa9148f96f 100644
--- a/tools/testing/selftests/kvm/memslot_perf_test.c
+++ b/tools/testing/selftests/kvm/memslot_perf_test.c
@@ -245,27 +245,17 @@ static bool prepare_vm(struct vm_data *data, int nslots, uint64_t *maxslots,
void *guest_code, uint64_t mempages,
struct timespec *slot_runtime)
{
- uint32_t max_mem_slots;
uint64_t rempages;
uint64_t guest_addr;
uint32_t slot;
struct timespec tstart;
struct sync_area *sync;
- max_mem_slots = kvm_check_cap(KVM_CAP_NR_MEMSLOTS);
- TEST_ASSERT(max_mem_slots > 1,
- "KVM_CAP_NR_MEMSLOTS should be greater than 1");
- TEST_ASSERT(nslots > 1 || nslots == -1,
- "Slot count cap should be greater than 1");
- if (nslots != -1)
- max_mem_slots = min(max_mem_slots, (uint32_t)nslots);
- pr_info_v("Allowed number of memory slots: %"PRIu32"\n", max_mem_slots);
-
TEST_ASSERT(mempages > 1,
"Can't test without any memory");
data->npages = mempages;
- data->nslots = max_mem_slots - 1;
+ data->nslots = nslots;
data->pages_per_slot = mempages / data->nslots;
if (!data->pages_per_slot) {
*maxslots = mempages + 1;
@@ -885,8 +875,8 @@ static bool parse_args(int argc, char *argv[],
break;
case 's':
targs->nslots = atoi(optarg);
- if (targs->nslots <= 0 && targs->nslots != -1) {
- pr_info("Slot count cap has to be positive or -1 for no cap\n");
+ if (targs->nslots <= 1 && targs->nslots != -1) {
+ pr_info("Slot count cap must be larger than 1 or -1 for no cap\n");
return false;
}
break;
@@ -932,6 +922,19 @@ static bool parse_args(int argc, char *argv[],
return false;
}
+ /* Memory slot 0 is reserved */
+ if (targs->nslots == -1) {
+ targs->nslots = kvm_check_cap(KVM_CAP_NR_MEMSLOTS) - 1;
+ if (targs->nslots < 1) {
+ pr_info("KVM_CAP_NR_MEMSLOTS should be greater than 1\n");
+ return false;
+ }
+ } else {
+ targs->nslots--;
+ }
+
+ pr_info_v("Number of memory slots: %d\n", targs->nslots);
+

Can't see any capping of the command line provided slot count to
KVM_CAP_NR_MEMSLOTS value, like the old code did.

return true;
}

Thanks,
Maciej