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

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Message-ID: <e2f344bd3c9f096e94889904f85333352dce0bcc.camel@redhat.com>
Date:   Wed, 11 Oct 2023 21:46:45 +0300
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     Dongli Zhang <dongli.zhang@...cle.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

У вт, 2023-10-10 у 09:31 -0700, Dongli Zhang пише:
> 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.


Sorry about this, I haven't noticed this code!


Best regards,
	Maxim Levitsky
> 
> +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
> > 
> >