On Tue, Oct 27, 2020 at 04:37:33PM -0700, Ben Gardon wrote:
The dirty log perf test will time verious dirty logging operations (enabling dirty logging, dirtying memory, getting the dirty log, clearing the dirty log, and disabling dirty logging) in order to quantify dirty logging performance. This test can be used to inform future performance improvements to KVM's dirty logging infrastructure.
One thing to mention is that there're a few patches in the kvm dirty ring series that reworked the dirty log test quite a bit (to add similar test for dirty ring). For example:
https://lore.kernel.org/kvm/20201023183358.50607-11-peterx@redhat.com/
Just a FYI if we're going to use separate test programs. Merging this tests should benefit in many ways, of course (e.g., dirty ring may directly runnable with the perf tests too; so we can manually enable this "perf mode" as a new parameter in dirty_log_test, if possible?), however I don't know how hard - maybe there's some good reason to keep them separate...
[...]
+static void run_test(enum vm_guest_mode mode, unsigned long iterations,
uint64_t phys_offset, int vcpus,uint64_t vcpu_memory_bytes, int wr_fract)+{
[...]
- /* Start the iterations */
- iteration = 0;
- host_quit = false;
- clock_gettime(CLOCK_MONOTONIC, &start);
- for (vcpu_id = 0; vcpu_id < vcpus; vcpu_id++) {
pthread_create(&vcpu_threads[vcpu_id], NULL, vcpu_worker,&perf_test_args.vcpu_args[vcpu_id]);- }
- /* Allow the vCPU to populate memory */
- pr_debug("Starting iteration %lu - Populating\n", iteration);
- while (READ_ONCE(vcpu_last_completed_iteration[vcpu_id]) != iteration)
pr_debug("Waiting for vcpu_last_completed_iteration == %lu\n",iteration);
Isn't array vcpu_last_completed_iteration[] initialized to all zeros? If so, I feel like this "while" won't run as expected to wait for populating mem.
The flooding pr_debug() seems a bit scary too if the mem size is huge.. How about a pr_debug() after the loop (so if we don't see that it means it hanged)?
(There's another similar pr_debug() after this point too within a loop)
Thanks,