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

Gleb Natapov
2011-06-16T12:21:55Z

On Thu, Jun 16, 2011 at 09:11:42AM -0300, Glauber Costa wrote:
> On 06/16/2011 08:27 AM, Gleb Natapov wrote:
> >On Thu, Jun 16, 2011 at 12:31:02AM -0300, Glauber Costa wrote:
> >>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.
> >>
> >The problem with this approach is that things like doing "info cpus"
> >in qemu monitor will change guest scheduling behaviour. Do we want it
> >to be like that?
>
> You mean because it is running in a different thread, and will
> compete for resources with the cpu thread ?
>
No, because it executes GET_REGS ioctl (in vcpu thread). The time
it takes to execute it is accounted as time the hypervior spent on behave
of a guest. Not a big deal if it is executed rarely. I tend to use "info
cpus"/"info register" quite a lot when debugging and would preffer it to
not affect guest behaviour.

> >>Which put/get are you referring to specifically ? You mean
> >>vcpu_put() vs vcpu_load() ?
> >>
> >Yes.
> >
> >>If they are after vcpu_put(), they will, because at this time your
> >>process is officially out of the cpu.
> >>
> >And if they are between vcpu_load() and vcpu_put() they will be accounted as
> >a work done on behalf of a guest although they are likely unrelated.
> I think the best we can do around it here is record steal time /
> measure time as late as we can. We could in theory subtract irq
> time, but it sounds too complicated for little gain.
>
Recording steal time/measure time as close as possible to vmentry/vmexit
is what I propose :) I agree about little gain part.

> >>
> >>>>
> >>>>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
> >>>>>>
> >>>>>>--
> >>>>>>To unsubscribe from this list: send the line "unsubscribe kvm" in
> >>>>>>the body of a message to majordomo@vger.kernel.org
> >>>>>>More majordomo info at http://vger.kernel.org/majordomo-info.html
> >>>>>
> >>>>>--
> >>>>> Gleb.
> >>>
> >>>--
> >>> Gleb.
> >
> >--
> > Gleb.

--
Gleb.