Re: [PATCH v2 2/2] KVM: selftests: access_tracking_perf_test: add option to skip the sanity check

[Maxim Levitsky]

On Tue, 2025-03-25 at 11:01 -0700, James Houghton wrote:
> On Mon, Mar 24, 2025 at 6:57 PM Maxim Levitsky <mlevitsk@xxxxxxxxxx> wrote:
> > Add an option to skip sanity check of number of still idle pages,
> > and set it by default to skip, in case hypervisor or NUMA balancing
> > is detected.
> > 
> > Signed-off-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx>
> 
> Thanks Maxim! I'm still working on a respin of this test with MGLRU
> integration, like [1]. Sorry it's taking me so long. I'll apply my
> changes on top of yours.
> 
> [1]: https://lore.kernel.org/kvm/20241105184333.2305744-12-jthoughton@xxxxxxxxxx/
> 
> > ---
> >  .../selftests/kvm/access_tracking_perf_test.c | 33 ++++++++++++++++---
> >  .../testing/selftests/kvm/include/test_util.h |  1 +
> >  tools/testing/selftests/kvm/lib/test_util.c   |  7 ++++
> >  3 files changed, 37 insertions(+), 4 deletions(-)
> > 
> > diff --git a/tools/testing/selftests/kvm/access_tracking_perf_test.c b/tools/testing/selftests/kvm/access_tracking_perf_test.c
> > index 3c7defd34f56..6d50c829f00c 100644
> > --- a/tools/testing/selftests/kvm/access_tracking_perf_test.c
> > +++ b/tools/testing/selftests/kvm/access_tracking_perf_test.c
> > @@ -65,6 +65,8 @@ static int vcpu_last_completed_iteration[KVM_MAX_VCPUS];
> >  /* Whether to overlap the regions of memory vCPUs access. */
> >  static bool overlap_memory_access;
> > 
> > +static int warn_on_too_many_idle_pages = -1;
> > +
> >  struct test_params {
> >         /* The backing source for the region of memory. */
> >         enum vm_mem_backing_src_type backing_src;
> > @@ -184,11 +186,10 @@ static void mark_vcpu_memory_idle(struct kvm_vm *vm,
> >          * are cached and the guest won't see the "idle" bit cleared.
> >          */
> >         if (still_idle >= pages / 10) {
> > -#ifdef __x86_64__
> > -               TEST_ASSERT(this_cpu_has(X86_FEATURE_HYPERVISOR),
> > +               TEST_ASSERT(warn_on_too_many_idle_pages,
> 
> I think this assertion is flipped (or how warn_on_too_many_idle_pages
> is being set is flipped, see below).
Yes it is no doubt about. 

I didn't notice this when I flipped the meaning
of the variable as Sean suggested.
Thanks!

Best regards,
	Maxim Levitsky


> 
> >                             "vCPU%d: Too many pages still idle (%lu out of %lu)",
> >                             vcpu_idx, still_idle, pages);
> > -#endif
> > +
> >                 printf("WARNING: vCPU%d: Too many pages still idle (%lu out of %lu), "
> >                        "this will affect performance results.\n",
> >                        vcpu_idx, still_idle, pages);
> > @@ -342,6 +343,8 @@ 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(" -w: Skip or force enable the check that after dirtying the guest memory, most (90%%) of \n"
> > +              "it is reported as dirty again (0/1)");
> >         backing_src_help("-s");
> >         puts("");
> >         exit(0);
> > @@ -359,7 +362,7 @@ int main(int argc, char *argv[])
> > 
> >         guest_modes_append_default();
> > 
> > -       while ((opt = getopt(argc, argv, "hm:b:v:os:")) != -1) {
> > +       while ((opt = getopt(argc, argv, "hm:b:v:os:w:")) != -1) {
> >                 switch (opt) {
> >                 case 'm':
> >                         guest_modes_cmdline(optarg);
> > @@ -376,6 +379,11 @@ int main(int argc, char *argv[])
> >                 case 's':
> >                         params.backing_src = parse_backing_src_type(optarg);
> >                         break;
> > +               case 'w':
> > +                       warn_on_too_many_idle_pages =
> > +                               atoi_non_negative("1 - enable warning, 0 - disable",
> > +                                                 optarg);
> 
> We still get a "warning" either way, right? Maybe this should be
> called "fail_on_too_many_idle_pages" (in which case the above
> assertion is indeed flipped). Or "warn_on_too_many_idle_pages" should
> mean *only* warn, i.e., *don't* fail, in which case, below we need to
> flip how we set it below.
> 
> > +                       break;
> >                 case 'h':
> >                 default:
> >                         help(argv[0]);
> > @@ -386,6 +394,23 @@ int main(int argc, char *argv[])
> >         page_idle_fd = open("/sys/kernel/mm/page_idle/bitmap", O_RDWR);
> >         __TEST_REQUIRE(page_idle_fd >= 0,
> >                        "CONFIG_IDLE_PAGE_TRACKING is not enabled");
> > +       if (warn_on_too_many_idle_pages == -1) {
> > +#ifdef __x86_64__
> > +               if (this_cpu_has(X86_FEATURE_HYPERVISOR)) {
> > +                       printf("Skipping idle page count sanity check, because the test is run nested\n");
> > +                       warn_on_too_many_idle_pages = 0;
> > +               } else
> > +#endif
> > +               if (is_numa_balancing_enabled()) {
> > +                       printf("Skipping idle page count sanity check, because NUMA balance is enabled\n");
> > +                       warn_on_too_many_idle_pages = 0;
> > +               } else {
> > +                       warn_on_too_many_idle_pages = 1;
> > +               }
> > +       } else if (!warn_on_too_many_idle_pages) {
> > +               printf("Skipping idle page count sanity check, because this was requested by the user\n");
> > +       }
> > +
> >         close(page_idle_fd);
> > 
> >         for_each_guest_mode(run_test, &params);
> > diff --git a/tools/testing/selftests/kvm/include/test_util.h b/tools/testing/selftests/kvm/include/test_util.h
> > index 3e473058849f..1bc9b0a92427 100644
> > --- a/tools/testing/selftests/kvm/include/test_util.h
> > +++ b/tools/testing/selftests/kvm/include/test_util.h
> > @@ -153,6 +153,7 @@ bool is_backing_src_hugetlb(uint32_t i);
> >  void backing_src_help(const char *flag);
> >  enum vm_mem_backing_src_type parse_backing_src_type(const char *type_name);
> >  long get_run_delay(void);
> > +bool is_numa_balancing_enabled(void);
> > 
> >  /*
> >   * Whether or not the given source type is shared memory (as opposed to
> > diff --git a/tools/testing/selftests/kvm/lib/test_util.c b/tools/testing/selftests/kvm/lib/test_util.c
> > index 3dc8538f5d69..03eb99af9b8d 100644
> > --- a/tools/testing/selftests/kvm/lib/test_util.c
> > +++ b/tools/testing/selftests/kvm/lib/test_util.c
> > @@ -176,6 +176,13 @@ size_t get_trans_hugepagesz(void)
> >         return get_sysfs_val("/sys/kernel/mm/transparent_hugepage/hpage_pmd_size");
> >  }
> > 
> > +bool is_numa_balancing_enabled(void)
> > +{
> > +       if (!test_sysfs_path("/proc/sys/kernel/numa_balancing"))
> > +               return false;
> > +       return get_sysfs_val("/proc/sys/kernel/numa_balancing") == 1;
> > +}
> > +
> >  size_t get_def_hugetlb_pagesz(void)
> >  {
> >         char buf[64];
> > --
> > 2.26.3
> >