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

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On 10/18/22 1:34 AM, Maciej S. Szmigiero wrote:
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.


Indeed. I wanted to avoid extra variable @max_mem_slots and the
capping is missed. I will fix it up in next revision.

      return true;
  }

Thanks,
Gavin

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