KVM: selftests: Introduce access_tracking_perf_test
This test measures the performance effects of KVM's access tracking.
Access tracking is driven by the MMU notifiers test_young, clear_young,
and clear_flush_young. These notifiers do not have a direct userspace
API, however the clear_young notifier can be triggered by marking a
pages as idle in /sys/kernel/mm/page_idle/bitmap. This test leverages
that mechanism to enable access tracking on guest memory.
To measure performance this test runs a VM with a configurable number of
vCPUs that each touch every page in disjoint regions of memory.
Performance is measured in the time it takes all vCPUs to finish
touching their predefined region.
$ ./access_tracking_perf_test -v 8
Testing guest mode: PA-bits:ANY, VA-bits:48, 4K pages
guest physical test memory offset: 0xffdfffff000
Populating memory : 1.337752570s
Writing to populated memory : 0.010177640s
Reading from populated memory : 0.009548239s
Mark memory idle : 23.973131748s
Writing to idle memory : 0.063584496s
Mark memory idle : 24.924652964s
Reading from idle memory : 0.062042814s
Breaking down the results:
* "Populating memory": The time it takes for all vCPUs to perform the
first write to every page in their region.
* "Writing to populated memory" / "Reading from populated memory": The
time it takes for all vCPUs to write and read to every page in their
region after it has been populated. This serves as a control for the
* "Mark memory idle": The time it takes for every vCPU to mark every
page in their region as idle through page_idle.
* "Writing to idle memory" / "Reading from idle memory": The time it
takes for all vCPUs to write and read to every page in their region
after it has been marked idle.
This test should be portable across architectures but it is only enabled
for x86_64 since that's all I have tested.
Reviewed-by: Ben Gardon <firstname.lastname@example.org>
Signed-off-by: David Matlack <email@example.com>
Signed-off-by: Paolo Bonzini <firstname.lastname@example.org>
3 files changed