On Fri, Sep 09, 2022 at 10:26:10AM -0700, David Matlack wrote:
> On Fri, Sep 09, 2022 at 12:43:00PM +0000, Colton Lewis wrote:
> > Create the ability to randomize page access order with the -a
> > argument, including the possibility that the same pages may be hit
> > multiple times during an iteration or not at all.
> >
> > Population sets random access to false.
>
> Please make sure to also explain the why in addition to the what.
>
> >
> > Signed-off-by: Colton Lewis <coltonlewis@xxxxxxxxxx>
> > ---
> > tools/testing/selftests/kvm/dirty_log_perf_test.c | 11 +++++++++--
> > .../selftests/kvm/include/perf_test_util.h | 2 ++
> > tools/testing/selftests/kvm/lib/perf_test_util.c | 15 ++++++++++++++-
> > 3 files changed, 25 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 c2ad299b3760..3639d5f95033 100644
> > --- a/tools/testing/selftests/kvm/dirty_log_perf_test.c
> > +++ b/tools/testing/selftests/kvm/dirty_log_perf_test.c
> > @@ -127,6 +127,7 @@ struct test_params {
> > int slots;
> > uint32_t write_percent;
> > uint32_t random_seed;
> > + bool random_access;
> > };
> >
> > static void toggle_dirty_logging(struct kvm_vm *vm, int slots, bool enable)
> > @@ -248,6 +249,7 @@ static void run_test(enum vm_guest_mode mode, void *arg)
> > vcpu_last_completed_iteration[vcpu_id] = -1;
> >
> > perf_test_set_write_percent(vm, 100);
> > + perf_test_set_random_access(vm, false);
> > perf_test_start_vcpu_threads(nr_vcpus, vcpu_worker);
> >
> > /* Allow the vCPUs to populate memory */
> > @@ -270,6 +272,7 @@ static void run_test(enum vm_guest_mode mode, void *arg)
> > ts_diff.tv_sec, ts_diff.tv_nsec);
> >
> > perf_test_set_write_percent(vm, p->write_percent);
> > + perf_test_set_random_access(vm, p->random_access);
> >
> > while (iteration < p->iterations) {
> > /*
> > @@ -341,10 +344,11 @@ static void run_test(enum vm_guest_mode mode, void *arg)
> > static void help(char *name)
> > {
> > puts("");
> > - printf("usage: %s [-h] [-i iterations] [-p offset] [-g] "
> > + printf("usage: %s [-h] [-a] [-i iterations] [-p offset] [-g] "
> > "[-m mode] [-n] [-b vcpu bytes] [-v vcpus] [-o] [-r random seed ] [-s mem type]"
> > "[-x memslots] [-w percentage]\n", name);
> > puts("");
> > + printf(" -a: access memory randomly rather than in order.\n");
> > printf(" -i: specify iteration counts (default: %"PRIu64")\n",
> > TEST_HOST_LOOP_N);
> > printf(" -g: Do not enable KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2. This\n"
> > @@ -396,8 +400,11 @@ int main(int argc, char *argv[])
> >
> > guest_modes_append_default();
> >
> > - while ((opt = getopt(argc, argv, "ghi:p:m:nb:v:or:s:x:w:")) != -1) {
> > + while ((opt = getopt(argc, argv, "aghi:p:m:nb:v:or:s:x:w:")) != -1) {
> > switch (opt) {
> > + case 'a':
> > + p.random_access = true;
> > + break;
> > case 'g':
> > dirty_log_manual_caps = 0;
> > break;
> > diff --git a/tools/testing/selftests/kvm/include/perf_test_util.h b/tools/testing/selftests/kvm/include/perf_test_util.h
> > index f93f2ea7c6a3..d9664a31e01c 100644
> > --- a/tools/testing/selftests/kvm/include/perf_test_util.h
> > +++ b/tools/testing/selftests/kvm/include/perf_test_util.h
> > @@ -39,6 +39,7 @@ struct perf_test_args {
> >
> > /* Run vCPUs in L2 instead of L1, if the architecture supports it. */
> > bool nested;
> > + bool random_access;
> >
> > struct perf_test_vcpu_args vcpu_args[KVM_MAX_VCPUS];
> > };
> > @@ -53,6 +54,7 @@ void perf_test_destroy_vm(struct kvm_vm *vm);
> >
> > 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_set_random_access(struct kvm_vm *vm, bool random_access);
> >
> > 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 12a3597be1f9..ce657fa92f05 100644
> > --- a/tools/testing/selftests/kvm/lib/perf_test_util.c
> > +++ b/tools/testing/selftests/kvm/lib/perf_test_util.c
> > @@ -46,6 +46,7 @@ void perf_test_guest_code(uint32_t vcpu_id)
> > struct perf_test_vcpu_args *vcpu_args = &pta->vcpu_args[vcpu_id];
> > uint64_t gva;
> > uint64_t pages;
> > + uint64_t addr;
> > int i;
> > uint32_t rand = pta->random_seed + vcpu_id;
> >
> > @@ -57,7 +58,13 @@ void perf_test_guest_code(uint32_t vcpu_id)
> >
> > while (true) {
> > for (i = 0; i < pages; i++) {
> > - uint64_t addr = gva + (i * pta->guest_page_size);
> > + guest_random(&rand);
> > +
> > + if (pta->random_access)
> > + addr = gva + ((rand % pages) * pta->guest_page_size);
> > + else
> > + addr = gva + (i * pta->guest_page_size);
> > +
> > guest_random(&rand);
>
> Is it on purpose use a separate random number for access offset and
> read/write?
>
It's because of the following, from https://lore.kernel.org/kvm/YxDvVyFpMC9U3O25@xxxxxxxxxx/
I think addr and write_percent need two different random numbers.
Otherwise, you will end up with a situation where all addresses where
(rnd_arr[i] % 100 < pta->write_percent) will get a write (always).
Something like this:
012345678 <= address
wwwrrrwww
837561249 <= access order
I think the best way to fix this is to abstract the random number
reading into something like get_next_rand(), and use it twice per
iteration.
> >
> > if (rand % 100 < pta->write_percent)
> > @@ -233,6 +240,12 @@ void perf_test_set_random_seed(struct kvm_vm *vm, uint32_t random_seed)
> > sync_global_to_guest(vm, perf_test_args.random_seed);
> > }
> >
> > +void perf_test_set_random_access(struct kvm_vm *vm, bool random_access)
> > +{
> > + perf_test_args.random_access = random_access;
> > + sync_global_to_guest(vm, perf_test_args.random_access);
> > +}
> > +
> > uint64_t __weak perf_test_nested_pages(int nr_vcpus)
> > {
> > return 0;
> > --
> > 2.37.2.789.g6183377224-goog
> >
