On Fri, Sep 9, 2022 at 10:31 AM Ricardo Koller <ricarkol@xxxxxxxxxx> wrote:
>
> 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.
Makes sense. Depending on how many bits of randomness we need (e.g.
read/write only needs 7) we could still use one random number. But the
bit manipulation would probably more complex than just generating
another random number (which looks like a fairly cheap calculation).
Colton can you add a comment here to explain the subtlety?
>
> > >
> > > 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
> > >
