Re: [PATCH 1/1] selftests: KVM: add test to print boottime wallclock

[Maxim Levitsky <mlevitsk@redhat.com>]

У пт, 2023-10-06 у 10:57 -0700, Dongli Zhang пише:
> As inspired by the discussion in [1], the boottime wallclock may drift due
> to the fact that the masterclock (or host monotonic clock) and kvmclock are
> calculated based on the algorithms in different domains.
> 
> This is to introduce a testcase to print the boottime wallclock
> periodically to help diagnose the wallclock drift issue in the future.
> 
> The idea is to wrmsr the MSR_KVM_WALL_CLOCK_NEW, and read the boottime
> wallclock nanoseconds immediately.
> 
> References:
> [1] https://lore.kernel.org/all/20231001111313.77586-1-nsaenz@amazon.com
> 
> Cc: David Woodhouse <dwmw@amazon.co.uk>
> Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
> ---
>  tools/testing/selftests/kvm/Makefile          |   3 +-
>  .../selftests/kvm/x86_64/boottime_wallclock.c | 100 ++++++++++++++++++
>  2 files changed, 102 insertions(+), 1 deletion(-)
>  create mode 100644 tools/testing/selftests/kvm/x86_64/boottime_wallclock.c
> 
> diff --git a/tools/testing/selftests/kvm/Makefile b/tools/testing/selftests/kvm/Makefile
> index a3bb36fb3cfc..fea05b0118de 100644
> --- a/tools/testing/selftests/kvm/Makefile
> +++ b/tools/testing/selftests/kvm/Makefile
> @@ -60,7 +60,8 @@ LIBKVM_riscv += lib/riscv/ucall.c
>  TEST_PROGS_x86_64 += x86_64/nx_huge_pages_test.sh
>  
>  # Compiled test targets
> -TEST_GEN_PROGS_x86_64 = x86_64/cpuid_test
> +TEST_GEN_PROGS_x86_64 = x86_64/boottime_wallclock
> +TEST_GEN_PROGS_x86_64 += x86_64/cpuid_test
>  TEST_GEN_PROGS_x86_64 += x86_64/cr4_cpuid_sync_test
>  TEST_GEN_PROGS_x86_64 += x86_64/dirty_log_page_splitting_test
>  TEST_GEN_PROGS_x86_64 += x86_64/get_msr_index_features
> diff --git a/tools/testing/selftests/kvm/x86_64/boottime_wallclock.c b/tools/testing/selftests/kvm/x86_64/boottime_wallclock.c
> new file mode 100644
> index 000000000000..cc48c9b19920
> --- /dev/null
> +++ b/tools/testing/selftests/kvm/x86_64/boottime_wallclock.c
> @@ -0,0 +1,100 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Copyright (C) 2023 Oracle and/or its affiliates.
> + */
> +
> +#include <asm/kvm_para.h>
> +#include <asm/pvclock-abi.h>
> +
> +#include "kvm_util.h"
> +#include "processor.h"
> +
> +static int period = 10;
> +
> +#define GUEST_SYNC_WALLCLOCK(__stage, __val)                        \
> +		GUEST_SYNC_ARGS(__stage, __val, 0, 0, 0)
> +
> +static void guest_main(vm_paddr_t wc_pa, struct pvclock_wall_clock *wc)
> +{
> +	uint64_t wallclock;
> +
> +	while (true) {
> +		wrmsr(MSR_KVM_WALL_CLOCK_NEW, wc_pa);
> +
> +		wallclock = wc->sec * NSEC_PER_SEC + wc->nsec;
> +
> +		GUEST_SYNC_WALLCLOCK(0, wallclock);

Won't this fill the output very fast?
Do you think it will be worth it to wait some time (e.g 1 second or at least 1/10 of a second)
between each print?

> +	}
> +}
> +
> +static void handle_sync(struct ucall *uc)
> +{
> +	uint64_t wallclock;
> +
> +	wallclock = uc->args[2];
> +
> +	pr_info("Boottime wallclock value: %"PRIu64" ns\n", wallclock);
> +}
> +
> +static void handle_abort(struct ucall *uc)
> +{
> +	REPORT_GUEST_ASSERT(*uc);
> +}
> +
> +static void enter_guest(struct kvm_vcpu *vcpu)
> +{
> +	struct ucall uc;
> +
> +	while (true) {
> +		vcpu_run(vcpu);
> +
> +		TEST_ASSERT_KVM_EXIT_REASON(vcpu, KVM_EXIT_IO);
> +
> +		switch (get_ucall(vcpu, &uc)) {
> +		case UCALL_SYNC:
> +			handle_sync(&uc);
> +			break;
> +		case UCALL_ABORT:
> +			handle_abort(&uc);
> +			return;
> +		default:
> +			TEST_ASSERT(0, "unhandled ucall: %ld\n", uc.cmd);
> +			return;
> +		}
> +
> +		sleep(period);
> +	}
> +}
> +
> +int main(int argc, char *argv[])
> +{
> +	struct kvm_vcpu *vcpu;
> +	struct kvm_vm *vm;
> +	vm_vaddr_t wc_gva;
> +	vm_paddr_t wc_gpa;
> +	int opt;
> +
> +	while ((opt = getopt(argc, argv, "p:h")) != -1) {
> +		switch (opt) {
> +		case 'p':
> +			period = atoi_positive("The period (seconds)", optarg);
> +			break;
> +		case 'h':
> +		default:
> +			pr_info("usage: %s [-p period (seconds)]\n", argv[0]);
> +			exit(1);
> +		}
> +	}
> +
> +	pr_info("Capture boottime wallclock every %d seconds.\n", period);
> +	pr_info("Stop with Ctrl + c.\n\n");
> +
> +	vm = vm_create_with_one_vcpu(&vcpu, guest_main);
> +
> +	wc_gva = vm_vaddr_alloc(vm, getpagesize(), 0x10000);
> +	wc_gpa = addr_gva2gpa(vm, wc_gva);
> +	vcpu_args_set(vcpu, 2, wc_gpa, wc_gva);
> +
> +	enter_guest(vcpu);
> +	kvm_vm_free(vm);
> +}


Best regards,
	Maxim Levitsky