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[34.82.181.220]) by smtp.gmail.com with ESMTPSA id b3-20020a170902650300b0016f1319d2a7sm1907904plk.297.2022.09.06.12.01.34 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 06 Sep 2022 12:01:35 -0700 (PDT) Date: Tue, 6 Sep 2022 12:01:31 -0700 From: Ricardo Koller To: Colton Lewis Cc: kvm@vger.kernel.org, pbonzini@redhat.com, maz@kernel.org, dmatlack@google.com, seanjc@google.com, oupton@google.com Subject: Re: [PATCH v3 1/3] KVM: selftests: Implement random number generation for guest code. Message-ID: References: <20220901195237.2152238-1-coltonlewis@google.com> <20220901195237.2152238-2-coltonlewis@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220901195237.2152238-2-coltonlewis@google.com> Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Thu, Sep 01, 2022 at 07:52:35PM +0000, Colton Lewis wrote: > Implement random number generation for guest code to randomize parts > of the test, making it less predictable and a more accurate reflection > of reality. > > Create a -r argument to specify a random seed. If no argument is > provided, the seed defaults to the current Unix timestamp. > > The random number generator chosen is the Park-Miller Linear > Congruential Generator, a fancy name for a basic and well-understood > random number generator entirely sufficient for this purpose. Each > vCPU calculates its own seed by adding its index to the seed provided. > > Signed-off-by: Colton Lewis > --- > .../selftests/kvm/dirty_log_perf_test.c | 12 ++++++++++-- > .../selftests/kvm/include/perf_test_util.h | 2 ++ > .../testing/selftests/kvm/lib/perf_test_util.c | 18 +++++++++++++++++- > 3 files changed, 29 insertions(+), 3 deletions(-) > > diff --git a/tools/testing/selftests/kvm/dirty_log_perf_test.c b/tools/testing/selftests/kvm/dirty_log_perf_test.c > index d60a34cdfaee..2f91acd94130 100644 > --- a/tools/testing/selftests/kvm/dirty_log_perf_test.c > +++ b/tools/testing/selftests/kvm/dirty_log_perf_test.c > @@ -126,6 +126,7 @@ struct test_params { > bool partition_vcpu_memory_access; > enum vm_mem_backing_src_type backing_src; > int slots; > + uint32_t random_seed; > }; > > static void toggle_dirty_logging(struct kvm_vm *vm, int slots, bool enable) > @@ -220,6 +221,8 @@ static void run_test(enum vm_guest_mode mode, void *arg) > p->slots, p->backing_src, > p->partition_vcpu_memory_access); > > + pr_info("Random seed: %u\n", p->random_seed); > + perf_test_set_random_seed(vm, p->random_seed); > perf_test_set_wr_fract(vm, p->wr_fract); > > guest_num_pages = (nr_vcpus * guest_percpu_mem_size) >> vm_get_page_shift(vm); > @@ -337,7 +340,7 @@ static void help(char *name) > { > puts(""); > printf("usage: %s [-h] [-i iterations] [-p offset] [-g] " > - "[-m mode] [-n] [-b vcpu bytes] [-v vcpus] [-o] [-s mem type]" > + "[-m mode] [-n] [-b vcpu bytes] [-v vcpus] [-o] [-r random seed ] [-s mem type]" > "[-x memslots]\n", name); > puts(""); > printf(" -i: specify iteration counts (default: %"PRIu64")\n", > @@ -362,6 +365,7 @@ static void help(char *name) > 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"); > + printf(" -r: specify the starting random seed.\n"); > backing_src_help("-s"); > printf(" -x: Split the memory region into this number of memslots.\n" > " (default: 1)\n"); > @@ -378,6 +382,7 @@ int main(int argc, char *argv[]) > .partition_vcpu_memory_access = true, > .backing_src = DEFAULT_VM_MEM_SRC, > .slots = 1, > + .random_seed = time(NULL), > }; > int opt; > > @@ -388,7 +393,7 @@ int main(int argc, char *argv[]) > > guest_modes_append_default(); > > - while ((opt = getopt(argc, argv, "ghi:p:m:nb:f:v:os:x:")) != -1) { > + while ((opt = getopt(argc, argv, "ghi:p:m:nb:f:v:or:s:x:")) != -1) { > switch (opt) { > case 'g': > dirty_log_manual_caps = 0; > @@ -421,6 +426,9 @@ int main(int argc, char *argv[]) > case 'o': > p.partition_vcpu_memory_access = false; > break; > + case 'r': > + p.random_seed = atoi(optarg); > + break; > case 's': > p.backing_src = parse_backing_src_type(optarg); > break; > diff --git a/tools/testing/selftests/kvm/include/perf_test_util.h b/tools/testing/selftests/kvm/include/perf_test_util.h > index d822cb670f1c..f18530984b42 100644 > --- a/tools/testing/selftests/kvm/include/perf_test_util.h > +++ b/tools/testing/selftests/kvm/include/perf_test_util.h > @@ -34,6 +34,7 @@ struct perf_test_args { > uint64_t gpa; > uint64_t size; > uint64_t guest_page_size; > + uint32_t random_seed; > int wr_fract; > > /* Run vCPUs in L2 instead of L1, if the architecture supports it. */ > @@ -51,6 +52,7 @@ struct kvm_vm *perf_test_create_vm(enum vm_guest_mode mode, int vcpus, > 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_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 *)); > void perf_test_join_vcpu_threads(int vcpus); > diff --git a/tools/testing/selftests/kvm/lib/perf_test_util.c b/tools/testing/selftests/kvm/lib/perf_test_util.c > index f989ff91f022..1292ed7d1193 100644 > --- a/tools/testing/selftests/kvm/lib/perf_test_util.c > +++ b/tools/testing/selftests/kvm/lib/perf_test_util.c > @@ -36,6 +36,13 @@ static void (*vcpu_thread_fn)(struct perf_test_vcpu_args *); > /* Set to true once all vCPU threads are up and running. */ > static bool all_vcpu_threads_running; > > + > +/* Park-Miller LCG using standard constants */ > +static uint32_t perf_test_random(uint32_t seed) > +{ > + return (uint64_t)seed * 48271 % ((uint32_t)(1 << 31) - 1); > +} Nit: I would prefer moving this to include/kvm_test_util.h, maybe something like: get_next_random(seed). There could be other users of this. > + > /* > * Continuously write to the first 8 bytes of each page in the > * specified region. > @@ -47,6 +54,7 @@ void perf_test_guest_code(uint32_t vcpu_id) > uint64_t gva; > uint64_t pages; > int i; > + uint32_t rand = pta->random_seed + vcpu_id; > > /* Make sure vCPU args data structure is not corrupt. */ > GUEST_ASSERT(vcpu_args->vcpu_id == vcpu_id); > @@ -56,6 +64,7 @@ void perf_test_guest_code(uint32_t vcpu_id) > > while (true) { > for (i = 0; i < pages; i++) { > + rand = perf_test_random(rand); > uint64_t addr = gva + (i * pta->guest_page_size); > > if (i % pta->wr_fract == 0) > @@ -115,8 +124,9 @@ struct kvm_vm *perf_test_create_vm(enum vm_guest_mode mode, int vcpus, > > pr_info("Testing guest mode: %s\n", vm_guest_mode_string(mode)); > > - /* By default vCPUs will write to memory. */ > + /* Set perf_test_args defaults. */ > pta->wr_fract = 1; > + pta->random_seed = time(NULL); > > /* > * Snapshot the non-huge page size. This is used by the guest code to > @@ -224,6 +234,12 @@ void perf_test_set_wr_fract(struct kvm_vm *vm, int wr_fract) > sync_global_to_guest(vm, perf_test_args); > } > > +void perf_test_set_random_seed(struct kvm_vm *vm, uint32_t random_seed) > +{ > + perf_test_args.random_seed = random_seed; > + sync_global_to_guest(vm, perf_test_args); > +} > + > uint64_t __weak perf_test_nested_pages(int nr_vcpus) > { > return 0; > -- > 2.37.2.789.g6183377224-goog >