Re: [PATCH v2 2/3] KVM: selftests: Randomize which pages are written vs read.

[David Matlack <dmatlack@google.com>]

On Wed, Aug 17, 2022 at 09:41:45PM +0000, Colton Lewis wrote:
> Randomize which tables are written vs read using the random number
> arrays. Change the variable wr_fract and associated function calls to
> write_percent that now operates as a percentage from 0 to 100 where X
> means each page has an X% chance of being written. Change the -f
> argument to -w to reflect the new variable semantics. Keep the same
> default of 100 percent writes.

Doesn't the new option cause like a 1000x slowdown in "Dirty memory
time"?  I don't think we should merge this until that is understood and
addressed (and it should be at least called out here so that reviewers
can be made aware).

> 
> Signed-off-by: Colton Lewis <coltonlewis@google.com>
> ---
>  .../selftests/kvm/access_tracking_perf_test.c |  2 +-
>  .../selftests/kvm/dirty_log_perf_test.c       | 28 ++++++++++---------
>  .../selftests/kvm/include/perf_test_util.h    |  4 +--
>  .../selftests/kvm/lib/perf_test_util.c        |  9 +++---
>  4 files changed, 23 insertions(+), 20 deletions(-)
> 
> diff --git a/tools/testing/selftests/kvm/access_tracking_perf_test.c b/tools/testing/selftests/kvm/access_tracking_perf_test.c
> index 1c2749b1481a..e87696b60e0f 100644
> --- a/tools/testing/selftests/kvm/access_tracking_perf_test.c
> +++ b/tools/testing/selftests/kvm/access_tracking_perf_test.c
> @@ -272,7 +272,7 @@ static void run_iteration(struct kvm_vm *vm, int nr_vcpus, const char *descripti
>  static void access_memory(struct kvm_vm *vm, int nr_vcpus,
>  			  enum access_type access, const char *description)
>  {
> -	perf_test_set_wr_fract(vm, (access == ACCESS_READ) ? INT_MAX : 1);
> +	perf_test_set_write_percent(vm, (access == ACCESS_READ) ? 0 : 100);
>  	iteration_work = ITERATION_ACCESS_MEMORY;
>  	run_iteration(vm, nr_vcpus, description);
>  }
> diff --git a/tools/testing/selftests/kvm/dirty_log_perf_test.c b/tools/testing/selftests/kvm/dirty_log_perf_test.c
> index 362b946019e9..9226eeea79bc 100644
> --- a/tools/testing/selftests/kvm/dirty_log_perf_test.c
> +++ b/tools/testing/selftests/kvm/dirty_log_perf_test.c
> @@ -128,10 +128,10 @@ static void vcpu_worker(struct perf_test_vcpu_args *vcpu_args)
>  struct test_params {
>  	unsigned long iterations;
>  	uint64_t phys_offset;
> -	int wr_fract;
>  	bool partition_vcpu_memory_access;
>  	enum vm_mem_backing_src_type backing_src;
>  	int slots;
> +	uint32_t write_percent;
>  	uint32_t random_seed;
>  };
>  
> @@ -227,7 +227,7 @@ static void run_test(enum vm_guest_mode mode, void *arg)
>  				 p->partition_vcpu_memory_access);
>  
>  	perf_test_set_random_seed(vm, p->random_seed);
> -	perf_test_set_wr_fract(vm, p->wr_fract);
> +	perf_test_set_write_percent(vm, p->write_percent);
>  
>  	guest_num_pages = (nr_vcpus * guest_percpu_mem_size) >> vm->page_shift;
>  	guest_num_pages = vm_adjust_num_guest_pages(mode, guest_num_pages);
> @@ -355,7 +355,7 @@ static void help(char *name)
>  	puts("");
>  	printf("usage: %s [-h] [-i iterations] [-p offset] [-g] "
>  	       "[-m mode] [-n] [-b vcpu bytes] [-v vcpus] [-o] [-r random seed ] [-s mem type]"
> -	       "[-x memslots]\n", name);
> +	       "[-x memslots] [-w percentage]\n", name);
>  	puts("");
>  	printf(" -i: specify iteration counts (default: %"PRIu64")\n",
>  	       TEST_HOST_LOOP_N);
> @@ -375,10 +375,6 @@ static void help(char *name)
>  	printf(" -b: specify the size of the memory region which should be\n"
>  	       "     dirtied by each vCPU. e.g. 10M or 3G.\n"
>  	       "     (default: 1G)\n");
> -	printf(" -f: specify the fraction of pages which should be written to\n"
> -	       "     as opposed to simply read, in the form\n"
> -	       "     1/<fraction of pages to write>.\n"
> -	       "     (default: 1 i.e. all pages are written to.)\n");
>  	printf(" -v: specify the number of vCPUs to run.\n");
>  	printf(" -o: Overlap guest memory accesses instead of partitioning\n"
>  	       "     them into a separate region of memory for each vCPU.\n");
> @@ -386,6 +382,11 @@ static void help(char *name)
>  	backing_src_help("-s");
>  	printf(" -x: Split the memory region into this number of memslots.\n"
>  	       "     (default: 1)\n");
> +	printf(" -w: specify the percentage of pages which should be written to\n"
> +	       "     as an integer from 0-100 inclusive. This is probabalistic,\n"
> +	       "     so -w X means each page has an X%% chance of writing\n"
> +	       "     and a (100-X)%% chance of reading.\n"
> +	       "     (default: 100 i.e. all pages are written to.)\n");
>  	puts("");
>  	exit(0);
>  }
> @@ -395,10 +396,10 @@ int main(int argc, char *argv[])
>  	int max_vcpus = kvm_check_cap(KVM_CAP_MAX_VCPUS);
>  	struct test_params p = {
>  		.iterations = TEST_HOST_LOOP_N,
> -		.wr_fract = 1,
>  		.partition_vcpu_memory_access = true,
>  		.backing_src = DEFAULT_VM_MEM_SRC,
>  		.slots = 1,
> +		.write_percent = 100,
>  		.random_seed = time(NULL),
>  	};
>  	int opt;
> @@ -410,7 +411,7 @@ int main(int argc, char *argv[])
>  
>  	guest_modes_append_default();
>  
> -	while ((opt = getopt(argc, argv, "eghi:p:m:nb:f:v:or:s:x:")) != -1) {
> +	while ((opt = getopt(argc, argv, "eghi:p:m:nb:v:or:s:x:w:")) != -1) {
>  		switch (opt) {
>  		case 'e':
>  			/* 'e' is for evil. */
> @@ -433,10 +434,11 @@ int main(int argc, char *argv[])
>  		case 'b':
>  			guest_percpu_mem_size = parse_size(optarg);
>  			break;
> -		case 'f':
> -			p.wr_fract = atoi(optarg);
> -			TEST_ASSERT(p.wr_fract >= 1,
> -				    "Write fraction cannot be less than one");
> +		case 'w':
> +			perf_test_args.write_percent = atoi(optarg);
> +			TEST_ASSERT(perf_test_args.write_percent >= 0
> +				    && perf_test_args.write_percent <= 100,
> +				    "Write percentage must be between 0 and 100");

perf_test_create_vm() overwrites this with 100. Did you mean
p.write_percent?

>  			break;
>  		case 'v':
>  			nr_vcpus = atoi(optarg);
> diff --git a/tools/testing/selftests/kvm/include/perf_test_util.h b/tools/testing/selftests/kvm/include/perf_test_util.h
> index 9517956424fc..8da4a839c585 100644
> --- a/tools/testing/selftests/kvm/include/perf_test_util.h
> +++ b/tools/testing/selftests/kvm/include/perf_test_util.h
> @@ -37,7 +37,7 @@ struct perf_test_args {
>  	uint64_t size;
>  	uint64_t guest_page_size;
>  	uint32_t random_seed;
> -	int wr_fract;
> +	int write_percent;
>  
>  	/* Run vCPUs in L2 instead of L1, if the architecture supports it. */
>  	bool nested;
> @@ -53,7 +53,7 @@ struct kvm_vm *perf_test_create_vm(enum vm_guest_mode mode, int nr_vcpus,
>  				   bool partition_vcpu_memory_access);
>  void perf_test_destroy_vm(struct kvm_vm *vm);
>  
> -void perf_test_set_wr_fract(struct kvm_vm *vm, int wr_fract);
> +void perf_test_set_write_percent(struct kvm_vm *vm, uint32_t write_percent);
>  void perf_test_set_random_seed(struct kvm_vm *vm, uint32_t random_seed);
>  
>  void perf_test_start_vcpu_threads(int vcpus, void (*vcpu_fn)(struct perf_test_vcpu_args *));
> diff --git a/tools/testing/selftests/kvm/lib/perf_test_util.c b/tools/testing/selftests/kvm/lib/perf_test_util.c
> index 8d85923acb4e..1a6b69713337 100644
> --- a/tools/testing/selftests/kvm/lib/perf_test_util.c
> +++ b/tools/testing/selftests/kvm/lib/perf_test_util.c
> @@ -48,6 +48,7 @@ void perf_test_guest_code(uint32_t vcpu_idx)
>  	struct perf_test_vcpu_args *vcpu_args = &pta->vcpu_args[vcpu_idx];
>  	uint64_t gva;
>  	uint64_t pages;
> +	uint32_t *rnd_arr = (uint32_t *)vcpu_args->random_array;
>  	int i;
>  
>  	gva = vcpu_args->gva;
> @@ -60,7 +61,7 @@ void perf_test_guest_code(uint32_t vcpu_idx)
>  		for (i = 0; i < pages; i++) {
>  			uint64_t addr = gva + (i * pta->guest_page_size);
>  
> -			if (i % pta->wr_fract == 0)
> +			if (rnd_arr[i] % 100 < pta->write_percent)
>  				*(uint64_t *)addr = 0x0123456789ABCDEF;
>  			else
>  				READ_ONCE(*(uint64_t *)addr);
> @@ -150,7 +151,7 @@ struct kvm_vm *perf_test_create_vm(enum vm_guest_mode mode, int nr_vcpus,
>  	pr_info("Testing guest mode: %s\n", vm_guest_mode_string(mode));
>  
>  	/* Set perf_test_args defaults. */
> -	pta->wr_fract = 100;
> +	pta->write_percent = 100;
>  	pta->random_seed = time(NULL);
>  
>  	/*
> @@ -258,9 +259,9 @@ void perf_test_destroy_vm(struct kvm_vm *vm)
>  	kvm_vm_free(vm);
>  }
>  
> -void perf_test_set_wr_fract(struct kvm_vm *vm, int wr_fract)
> +void perf_test_set_write_percent(struct kvm_vm *vm, uint32_t write_percent)
>  {
> -	perf_test_args.wr_fract = wr_fract;
> +	perf_test_args.write_percent = write_percent;
>  	sync_global_to_guest(vm, perf_test_args);
>  }
>  
> -- 
> 2.37.1.595.g718a3a8f04-goog
>