[RFC PATCH v4 0/3] KVM: selftests: Improvements on dirty-ring

[Leonardo Bras]

Add support to dirty-ring on dirty_log_perf_test, so we can measure
performance differences when we change / improve the mechanism.

One major conflict I had in this set is that dirty-ring needs to be
enabled after the VM was created, but before any cpu is created, so
for that, I made a few changes on memstress so it can actually take
dirty-ring size as a parameter for VM creation. (Patch #1)
I honestly don't think it's pretty, but I could not think on a
better way of doing this without messing too much in the code.

Also added some checks in dirty-ring enable, so an error message on
ring size is more informative.

Please provide feedback :)

Thanks!
Leo

Changes since RFCv3:
- Using acquire/release barriers to make sure there is no reorder between
  incrementing iteration and summing the time spent on cleaning.
- Improved ring-size checks, although not perfect due to reserved entries
  affecting minimum size.
- Do not allocate bitmaps for dirty-ring tests, as they are unused.
- Improve help text
- Make sure ret==0 before going back to vcpu_run in dirty-ring case
Link: https://lore.kernel.org/all/20260708152232.2568907-1-leo.bras@xxxxxxx/

Changes since RFCv2:
- Added mutex to make sure only a single vcpu is 
  collecting/cleaning at a time. This gets us the ability to
  test return values, and not account for kvm.slot_lock waiting time.
- Stuff reported by Sashiko
  - Return value always positive, so assert was pointless
  - Concurrency inflating the time for dirty-ring cleaning 
Link: https://lore.kernel.org/all/20260629105950.1790259-1-leo.bras@xxxxxxx/

Changes since RFCv1:
- Stuff reported by Sashiko
  - Fixed elements / byte size wrapping issue
  - Removed element count due to concurrency
  - Testing exit_reason instead of ioctl return value
  - Some nits
Link: https://lore.kernel.org/all/20260624171656.1737580-1-leo.bras@xxxxxxx/

Leonardo Bras (3):
  KVM: selftests: memstress: Add option to enable dirty-ring on VM
    creation
  KVM: selftests: Check dirty-ring size before enabling
  KVM: selftests: dirty_log_perf_test: Add dirty-ring support

 .../testing/selftests/kvm/include/memstress.h |   3 +-
 .../selftests/kvm/access_tracking_perf_test.c |   2 +-
 .../selftests/kvm/demand_paging_test.c        |   2 +-
 .../selftests/kvm/dirty_log_perf_test.c       | 128 ++++++++++++++++--
 tools/testing/selftests/kvm/lib/kvm_util.c    |  21 ++-
 tools/testing/selftests/kvm/lib/memstress.c   |  34 ++++-
 .../kvm/memslot_modification_stress_test.c    |   2 +-
 .../kvm/x86/dirty_log_page_splitting_test.c   |   2 +-
 8 files changed, 167 insertions(+), 27 deletions(-)


base-commit: f5098b6bae761e346ebcd9da7f95622c04733cff
-- 
2.55.0