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

Gleb Natapov
2011-06-16T11:27:25Z

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?

> 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.

>
> >>
> >>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.