linux-kernel - Re: [PATCH 3/6] KVM: selftests: memslot_perf

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Date:   Mon, 17 Oct 2022 19:34:42 +0200
From:   "Maciej S. Szmigiero" <mail@...iej.szmigiero.name>
To:     Gavin Shan <gshan@...hat.com>
Cc:     kvmarm@...ts.cs.columbia.edu, kvmarm@...ts.linux.dev,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        ajones@...tanamicro.com, pbonzini@...hat.com, maz@...nel.org,
        shuah@...nel.org, oliver.upton@...ux.dev, seanjc@...gle.com,
        peterx@...hat.com, ricarkol@...gle.com, zhenyzha@...hat.com,
        shan.gavin@...il.com
Subject: Re: [PATCH 3/6] KVM: selftests: memslot_perf_test: Probe memory slots
 for once

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@...hat.com>
> ---
>   .../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