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

[Gavin Shan]

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