If anyone has a chance to re-review this test patch series I'd be grateful. I responded to most of the feedback I received in the first series, and believe this test will be a useful performance benchmark for future development. On Mon, Dec 16, 2019 at 1:39 PM Ben Gardon <bgardon@xxxxxxxxxx> wrote: > > When handling page faults for many vCPUs during demand paging, KVM's MMU > lock becomes highly contended. This series creates a test with a naive > userfaultfd based demand paging implementation to demonstrate that > contention. This test serves both as a functional test of userfaultfd > and a microbenchmark of demand paging performance with a variable number > of vCPUs and memory per vCPU. > > The test creates N userfaultfd threads, N vCPUs, and a region of memory > with M pages per vCPU. The N userfaultfd polling threads are each set up > to serve faults on a region of memory corresponding to one of the vCPUs. > Each of the vCPUs is then started, and touches each page of its disjoint > memory region, sequentially. In response to faults, the userfaultfd > threads copy a static buffer into the guest's memory. This creates a > worst case for MMU lock contention as we have removed most of the > contention between the userfaultfd threads and there is no time required > to fetch the contents of guest memory. > > This test was run successfully on Intel Haswell, Broadwell, and > Cascadelake hosts with a variety of vCPU counts and memory sizes. > > This test was adapted from the dirty_log_test. > > The series can also be viewed in Gerrit here: > https://linux-review.googlesource.com/c/virt/kvm/kvm/+/1464 > (Thanks to Dmitry Vyukov <dvyukov@xxxxxxxxxx> for setting up the Gerrit > instance) > > Ben Gardon (9): > KVM: selftests: Create a demand paging test > KVM: selftests: Add demand paging content to the demand paging test > KVM: selftests: Add memory size parameter to the demand paging test > KVM: selftests: Pass args to vCPU instead of using globals > KVM: selftests: Support multiple vCPUs in demand paging test > KVM: selftests: Time guest demand paging > KVM: selftests: Add parameter to _vm_create for memslot 0 base paddr > KVM: selftests: Support large VMs in demand paging test > Add static flag > > tools/testing/selftests/kvm/.gitignore | 1 + > tools/testing/selftests/kvm/Makefile | 4 +- > .../selftests/kvm/demand_paging_test.c | 610 ++++++++++++++++++ > tools/testing/selftests/kvm/dirty_log_test.c | 2 +- > .../testing/selftests/kvm/include/kvm_util.h | 3 +- > tools/testing/selftests/kvm/lib/kvm_util.c | 7 +- > 6 files changed, 621 insertions(+), 6 deletions(-) > create mode 100644 tools/testing/selftests/kvm/demand_paging_test.c > > -- > 2.23.0.444.g18eeb5a265-goog >
