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Message-ID: <2604fa79-b114-60d9-c28d-0d53cd0dc5c7@oracle.com>
Date: Tue, 10 Oct 2023 09:31:18 -0700
From: Dongli Zhang <dongli.zhang@...cle.com>
To: Maxim Levitsky <mlevitsk@...hat.com>, kvm@...r.kernel.org,
linux-kselftest@...r.kernel.org
Cc: linux-kernel@...r.kernel.org, pbonzini@...hat.com,
shuah@...nel.org, seanjc@...gle.com, dwmw2@...radead.org,
joe.jin@...cle.com
Subject: Re: [PATCH 1/1] selftests: KVM: add test to print boottime wallclock
Hi Maxim,
On 10/10/23 09:13, Maxim Levitsky wrote:
> 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://urldefense.com/v3/__https://lore.kernel.org/all/20231001111313.77586-1-nsaenz@amazon.com__;!!ACWV5N9M2RV99hQ!MOnoujF4PlfvZ3SUuyXgIpJC5mWiE5uLUsNW6AWgirGXcObN5uil_fnthRVcYaPA0N2uoNyLChBogHC7ZS6t$
>>
>> Cc: David Woodhouse <dwmw@...zon.co.uk>
>> Signed-off-by: Dongli Zhang <dongli.zhang@...cle.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?
The wait time is controlled by the VMM side (of selftest) as in below.
In the while loop at VMM side, it sleeps for a period (configurable argument),
until it runs into the guest again.
Therefore, the user can decide the frequency to print the boottime wallclock.
+static void enter_guest(struct kvm_vcpu *vcpu)
+{
+ struct ucall uc;
+
+ while (true) {
+ vcpu_run(vcpu); -----------> to schedule guest vcpu here
+
+ 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); ------------> sleep here
+ }
+}
Thank you very much!
Dongli Zhang
>
>> + }
>> +}
>> +
>> +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
>
>
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