Re: [PATCH 3/7] KVM-HV: KVM Steal time implementation

Glauber Costa
2011-06-16T03:31:29Z

On 06/15/2011 06:09 AM, Gleb Natapov wrote:
> On Wed, Jun 15, 2011 at 12:09:31AM -0300, Glauber Costa wrote:
>> On 06/14/2011 04:45 AM, Gleb Natapov wrote:
>>> On Mon, Jun 13, 2011 at 07:31:33PM -0400, Glauber Costa wrote:
>>>> To implement steal time, we need the hypervisor to pass the guest information
>>>> about how much time was spent running other processes outside the VM.
>>>> This is per-vcpu, and using the kvmclock structure for that is an abuse
>>>> we decided not to make.
>>>>
>>>> In this patchset, I am introducing a new msr, KVM_MSR_STEAL_TIME, that
>>>> holds the memory area address containing information about steal time
>>>>
>>>> This patch contains the hypervisor part for it. I am keeping it separate from
>>>> the headers to facilitate backports to people who wants to backport the kernel
>>>> part but not the hypervisor, or the other way around.
>>>>
>>>> Signed-off-by: Glauber Costa<glommer@redhat.com>
>>>> CC: Rik van Riel<riel@redhat.com>
>>>> CC: Jeremy Fitzhardinge<jeremy.fitzhardinge@citrix.com>
>>>> CC: Peter Zijlstra<peterz@infradead.org>
>>>> CC: Avi Kivity<avi@redhat.com>
>>>> CC: Anthony Liguori<aliguori@us.ibm.com>
>>>> CC: Eric B Munson<emunson@mgebm.net>
>>>> ---
>>>> arch/x86/include/asm/kvm_host.h | 8 +++++
>>>> arch/x86/include/asm/kvm_para.h | 4 ++
>>>> arch/x86/kvm/x86.c | 60 +++++++++++++++++++++++++++++++++++++--
>>>> 3 files changed, 69 insertions(+), 3 deletions(-)
>>>>
>>>> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
>>>> index fc38eca..5dce014 100644
>>>> --- a/arch/x86/include/asm/kvm_host.h
>>>> +++ b/arch/x86/include/asm/kvm_host.h
>>>> @@ -388,6 +388,14 @@ struct kvm_vcpu_arch {
>>>> unsigned int hw_tsc_khz;
>>>> unsigned int time_offset;
>>>> struct page *time_page;
>>>> +
>>>> + struct {
>>>> + u64 msr_val;
>>>> + gpa_t stime;
>>>> + struct kvm_steal_time steal;
>>>> + u64 this_time_out;
>>>> + } st;
>>>> +
>>>> u64 last_guest_tsc;
>>>> u64 last_kernel_ns;
>>>> u64 last_tsc_nsec;
>>>> diff --git a/arch/x86/include/asm/kvm_para.h b/arch/x86/include/asm/kvm_para.h
>>>> index ac306c4..0341e61 100644
>>>> --- a/arch/x86/include/asm/kvm_para.h
>>>> +++ b/arch/x86/include/asm/kvm_para.h
>>>> @@ -45,6 +45,10 @@ struct kvm_steal_time {
>>>> __u32 pad[6];
>>>> };
>>>>
>>>> +#define KVM_STEAL_ALIGNMENT_BITS 5
>>>> +#define KVM_STEAL_VALID_BITS ((-1ULL<< (KVM_STEAL_ALIGNMENT_BITS + 1)))
>>>> +#define KVM_STEAL_RESERVED_MASK (((1<< KVM_STEAL_ALIGNMENT_BITS) - 1 )<< 1)
>>>> +
>>>> #define KVM_MAX_MMU_OP_BATCH 32
>>>>
>>>> #define KVM_ASYNC_PF_ENABLED (1<< 0)
>>>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>>>> index 6645634..10fe028 100644
>>>> --- a/arch/x86/kvm/x86.c
>>>> +++ b/arch/x86/kvm/x86.c
>>>> @@ -797,12 +797,12 @@ EXPORT_SYMBOL_GPL(kvm_get_dr);
>>>> * kvm-specific. Those are put in the beginning of the list.
>>>> */
>>>>
>>>> -#define KVM_SAVE_MSRS_BEGIN 8
>>>> +#define KVM_SAVE_MSRS_BEGIN 9
>>>> static u32 msrs_to_save[] = {
>>>> MSR_KVM_SYSTEM_TIME, MSR_KVM_WALL_CLOCK,
>>>> MSR_KVM_SYSTEM_TIME_NEW, MSR_KVM_WALL_CLOCK_NEW,
>>>> HV_X64_MSR_GUEST_OS_ID, HV_X64_MSR_HYPERCALL,
>>>> - HV_X64_MSR_APIC_ASSIST_PAGE, MSR_KVM_ASYNC_PF_EN,
>>>> + HV_X64_MSR_APIC_ASSIST_PAGE, MSR_KVM_ASYNC_PF_EN, MSR_KVM_STEAL_TIME,
>>>> MSR_IA32_SYSENTER_CS, MSR_IA32_SYSENTER_ESP, MSR_IA32_SYSENTER_EIP,
>>>> MSR_STAR,
>>>> #ifdef CONFIG_X86_64
>>>> @@ -1480,6 +1480,34 @@ static void kvmclock_reset(struct kvm_vcpu *vcpu)
>>>> }
>>>> }
>>>>
>>>> +static void record_steal_time(struct kvm_vcpu *vcpu)
>>>> +{
>>>> + u64 delta;
>>>> +
>>>> + if (vcpu->arch.st.stime&& vcpu->arch.st.this_time_out) {
>>>> +
>>>> + if (unlikely(kvm_read_guest(vcpu->kvm, vcpu->arch.st.stime,
>>>> + &vcpu->arch.st.steal, sizeof(struct kvm_steal_time)))) {
>>>> +
>>>> + vcpu->arch.st.stime = 0;
>>>> + return;
>>>> + }
>>>> +
>>>> + delta = (get_kernel_ns() - vcpu->arch.st.this_time_out);
>>>> +
>>>> + vcpu->arch.st.steal.steal += delta;
>>>> + vcpu->arch.st.steal.version += 2;
>>>> +
>>>> + if (unlikely(kvm_write_guest(vcpu->kvm, vcpu->arch.st.stime,
>>> Why not use kvm_write_guest_cached() here and introduce kvm_read_guest_cached()
>>> for the read above?
>>
>> Actually, I'd expect most read/writes to benefit from caching, no?
>> So why don't we just rename kvm_write_guest_cached() to
>> kvm_write_guest(), and the few places - if any - that need to force
>> transversing of the gfn mappings, get renamed to
>> kvm_write_guest_uncached ?
>>
> Good idea. I do not see any places where kvm_write_guest_uncached is
> needed from a brief look. Avi?
>
>>>> + &vcpu->arch.st.steal, sizeof(struct kvm_steal_time)))) {
>>>> +
>>>> + vcpu->arch.st.stime = 0;
>>>> + return;
>>>> + }
>>>> + }
>>>> +
>>>> +}
>>>> +
>>>> int kvm_set_msr_common(struct kvm_vcpu *vcpu, u32 msr, u64 data)
>>>> {
>>>> switch (msr) {
>>>> @@ -1562,6 +1590,23 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, u32 msr, u64 data)
>>>> if (kvm_pv_enable_async_pf(vcpu, data))
>>>> return 1;
>>>> break;
>>>> + case MSR_KVM_STEAL_TIME:
>>>> + vcpu->arch.st.msr_val = data;
>>>> +
>>>> + if (!(data& KVM_MSR_ENABLED)) {
>>>> + vcpu->arch.st.stime = 0;
>>>> + break;
>>>> + }
>>>> +
>>>> + if (data& KVM_STEAL_RESERVED_MASK)
>>>> + return 1;
>>>> +
>>>> + vcpu->arch.st.this_time_out = get_kernel_ns();
>>>> + vcpu->arch.st.stime = data& KVM_STEAL_VALID_BITS;
>>>> + record_steal_time(vcpu);
>>>> +
>>>> + break;
>>>> +
>>>> case MSR_IA32_MCG_CTL:
>>>> case MSR_IA32_MCG_STATUS:
>>>> case MSR_IA32_MC0_CTL ... MSR_IA32_MC0_CTL + 4 * KVM_MAX_MCE_BANKS - 1:
>>>> @@ -1847,6 +1892,9 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, u32 msr, u64 *pdata)
>>>> case MSR_KVM_ASYNC_PF_EN:
>>>> data = vcpu->arch.apf.msr_val;
>>>> break;
>>>> + case MSR_KVM_STEAL_TIME:
>>>> + data = vcpu->arch.st.msr_val;
>>>> + break;
>>>> case MSR_IA32_P5_MC_ADDR:
>>>> case MSR_IA32_P5_MC_TYPE:
>>>> case MSR_IA32_MCG_CAP:
>>>> @@ -2158,6 +2206,8 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
>>>> kvm_migrate_timers(vcpu);
>>>> vcpu->cpu = cpu;
>>>> }
>>>> +
>>>> + record_steal_time(vcpu);
>>>> }
>>>>
>>>> void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
>>>> @@ -2165,6 +2215,7 @@ void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
>>>> kvm_x86_ops->vcpu_put(vcpu);
>>>> kvm_put_guest_fpu(vcpu);
>>>> kvm_get_msr(vcpu, MSR_IA32_TSC,&vcpu->arch.last_guest_tsc);
>>>> + vcpu->arch.st.this_time_out = get_kernel_ns();
>>>> }
>>>>
>>> Shouldn't we call record_steal_time(vcpu)/vcpu->arch.st.this_time_out = get_kernel_ns();
>>> just before/after entering/exiting a guest? vcpu_(put|get) are called
>>> for each vcpu ioctl, not only VCPU_RUN.
>> Sorry, missed that the first time I've read your e-mail.
>>
>> If done like you said, time spent on the hypervisor is accounted as
>> steal time. I don't think it is.
> I thought that this is the point of a steal time. Running other
> tasks/guests is a hypervisor overhead too after all :) Also what about
> time spend serving host interrupts between put/get? It will not be
> accounted as steal time, correct?

This is mostly semantics. I like to compare this to a normal process:
There is a difference between time the OS spent on your behalf, doing
your system calls (sys), and time spent by other processes. Similar
thing here.

Which put/get are you referring to specifically ? You mean vcpu_put() vs
vcpu_load() ?

If they are after vcpu_put(), they will, because at this time your
process is officially out of the cpu.

>>
>> Steal time is time spent running someone else's job instead of
>> yours. The name for the time spent in the hypervisor doing something
>> for *you* is just overhead.
> OK. That is the question of a definition I guess. If you define it like
> that the code is correct.
>
>>
>>>
>>>> static int is_efer_nx(void)
>>>> @@ -2477,7 +2528,8 @@ static void do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
>>>> (1<< KVM_FEATURE_NOP_IO_DELAY) |
>>>> (1<< KVM_FEATURE_CLOCKSOURCE2) |
>>>> (1<< KVM_FEATURE_ASYNC_PF) |
>>>> - (1<< KVM_FEATURE_CLOCKSOURCE_STABLE_BIT);
>>>> + (1<< KVM_FEATURE_CLOCKSOURCE_STABLE_BIT) |
>>>> + (1<< KVM_FEATURE_STEAL_TIME);
>>>> entry->ebx = 0;
>>>> entry->ecx = 0;
>>>> entry->edx = 0;
>>>> @@ -6200,6 +6252,8 @@ int kvm_arch_vcpu_reset(struct kvm_vcpu *vcpu)
>>>>
>>>> kvmclock_reset(vcpu);
>>>>
>>>> + vcpu->arch.st.stime = 0;
>>>> +
>>>> kvm_clear_async_pf_completion_queue(vcpu);
>>>> kvm_async_pf_hash_reset(vcpu);
>>>> vcpu->arch.apf.halted = false;
>>>> --
>>>> 1.7.3.4
>>>>
>>>> --
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>>>
>>> --
>>> Gleb.
>
> --
> Gleb.