This patch introduces dynamic PLE window that is based on detecting potential undrcommit case patch series (patch 1 and RESENT patch 2) from the thread https://lkml.org/lkml/2012/10/29/287.
Results are on expected lines from the discussion of ple_window experiment where summary showed improvement for undercommit cases for ebizzy workload. link: https://lkml.org/lkml/2012/10/9/545 32 vcpu guest on 32 core (HT diabled) mx3850 PLE machine base = 3.7.0-rc1 A = base + bail out on successive failures patch. (link above) B = A + dynamic ple window patch (below patch) Results w.r.t base. (Tested only on x86_64) A B ebizzy_1x 147.47995 182.69864 ebizzy_2x -4.52835 -12.22457 ebizzy_3x -5.17241 -39.55113 dbench_1x 61.14888 54.31150 dbench_2x -4.17130 -6.15509 dbench_3x -3.18740 -9.63721 Result shows improvement for 1x ebizzy case. Comments/suggestions welcome. ----8<---- kvm: Add dynamic ple window feature From: Raghavendra K T <raghavendra...@linux.vnet.ibm.com> The current value of PLE window is tuned very well for overcommited cases. However for less than 1:1 overcommit, PLE is a big overhead. A PLE window of 16k is good for such cases. This patch adds the logic of dynamic PLE window, where, upon successful yield_to in PLE handler we decrement window size until 4k Similarly when we find yield_to have been unsuccessful, we increment until 16k. With this patchset we change the defult PLE window size to 16k. Signed-off-by: Raghavendra K T <raghavendra...@linux.vnet.ibm.com> --- arch/s390/include/asm/kvm_host.h | 2 ++ arch/x86/include/asm/kvm_host.h | 4 ++++ arch/x86/kvm/svm.c | 10 ++++++++++ arch/x86/kvm/vmx.c | 32 ++++++++++++++++++++++++++++++-- arch/x86/kvm/x86.c | 10 ++++++++++ virt/kvm/kvm_main.c | 5 +++++ 6 files changed, 61 insertions(+), 2 deletions(-) diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h index b784154..012b48d 100644 --- a/arch/s390/include/asm/kvm_host.h +++ b/arch/s390/include/asm/kvm_host.h @@ -257,4 +257,6 @@ struct kvm_arch{ }; extern int sie64a(struct kvm_s390_sie_block *, u64 *); +static inline void kvm_inc_ple_window(void) {} +static inline void kvm_dec_ple_window(void) {} #endif diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h index b2e11f4..4629e59 100644 --- a/arch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@ -707,6 +707,8 @@ struct kvm_x86_ops { int (*check_intercept)(struct kvm_vcpu *vcpu, struct x86_instruction_info *info, enum x86_intercept_stage stage); + void (*inc_ple_window)(void); + void (*dec_ple_window)(void); }; struct kvm_arch_async_pf { @@ -1007,5 +1009,7 @@ int kvm_pmu_set_msr(struct kvm_vcpu *vcpu, u32 msr, u64 data); int kvm_pmu_read_pmc(struct kvm_vcpu *vcpu, unsigned pmc, u64 *data); void kvm_handle_pmu_event(struct kvm_vcpu *vcpu); void kvm_deliver_pmi(struct kvm_vcpu *vcpu); +void kvm_inc_ple_window(void); +void kvm_dec_ple_window(void); #endif /* _ASM_X86_KVM_HOST_H */ diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c index d017df3..198523e 100644 --- a/arch/x86/kvm/svm.c +++ b/arch/x86/kvm/svm.c @@ -4220,6 +4220,14 @@ out: return ret; } +static inline void svm_inc_ple_window(void) +{ +} + +static inline void svm_dec_ple_window(void) +{ +} + static struct kvm_x86_ops svm_x86_ops = { .cpu_has_kvm_support = has_svm, .disabled_by_bios = is_disabled, @@ -4310,6 +4318,8 @@ static struct kvm_x86_ops svm_x86_ops = { .set_tdp_cr3 = set_tdp_cr3, .check_intercept = svm_check_intercept, + .inc_ple_window = svm_inc_ple_window, + .dec_ple_window = svm_dec_ple_window, }; static int __init svm_init(void) diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c index ad6b1dd..68fb3e4 100644 --- a/arch/x86/kvm/vmx.c +++ b/arch/x86/kvm/vmx.c @@ -115,12 +115,17 @@ module_param(nested, bool, S_IRUGO); * According to test, this time is usually smaller than 128 cycles. * ple_window: upper bound on the amount of time a guest is allowed to execute * in a PAUSE loop. Tests indicate that most spinlocks are held for - * less than 2^12 cycles + * less than 2^12 cycles. But we keep the default value 2^14 to + * ensure less overhead in uncontended cases. * Time is measured based on a counter that runs at the same rate as the TSC, * refer SDM volume 3b section 21.6.13 & 22.1.3. */ #define KVM_VMX_DEFAULT_PLE_GAP 128 -#define KVM_VMX_DEFAULT_PLE_WINDOW 4096 +#define KVM_VMX_DEFAULT_PLE_WINDOW 16384 +#define KVM_VMX_MAX_PLE_WINDOW 16384 +#define KVM_VMX_MIN_PLE_WINDOW 4096 +#define KVM_VMX_PLE_WINDOW_DELTA 1024 + static int ple_gap = KVM_VMX_DEFAULT_PLE_GAP; module_param(ple_gap, int, S_IRUGO); @@ -7149,6 +7154,27 @@ void load_vmcs12_host_state(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12) vmcs12->host_ia32_perf_global_ctrl); } +#define MAX(a, b) ((a) > (b) ? (a) : (b)) +#define MIN(a, b) ((a) < (b) ? (a) : (b)) + +static inline void vmx_inc_ple_window(void) +{ + if (ple_gap) { + ple_window = MIN(KVM_VMX_MAX_PLE_WINDOW, + ple_window + KVM_VMX_PLE_WINDOW_DELTA); + vmcs_write32(PLE_WINDOW, ple_window); + } +} + +static inline void vmx_dec_ple_window(void) +{ + if (ple_gap) { + ple_window = MAX(KVM_VMX_MIN_PLE_WINDOW, + ple_window - (KVM_VMX_PLE_WINDOW_DELTA>>2)); + vmcs_write32(PLE_WINDOW, ple_window); + } +} + /* * Emulate an exit from nested guest (L2) to L1, i.e., prepare to run L1 * and modify vmcs12 to make it see what it would expect to see there if @@ -7314,6 +7340,8 @@ static struct kvm_x86_ops vmx_x86_ops = { .set_tdp_cr3 = vmx_set_cr3, .check_intercept = vmx_check_intercept, + .inc_ple_window = vmx_inc_ple_window, + .dec_ple_window = vmx_dec_ple_window, }; static int __init vmx_init(void) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 224a7e7..7af4315 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -6052,6 +6052,16 @@ int kvm_arch_vcpu_setup(struct kvm_vcpu *vcpu) return r; } +void kvm_inc_ple_window(void) +{ + kvm_x86_ops->inc_ple_window(); +} + +void kvm_dec_ple_window(void) +{ + kvm_x86_ops->dec_ple_window(); +} + void kvm_arch_vcpu_destroy(struct kvm_vcpu *vcpu) { int r; diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 9f390e7..0272863 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -1731,15 +1731,20 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *me) yielded = kvm_vcpu_yield_to(vcpu); if (yielded > 0) { + kvm_dec_ple_window(); kvm->last_boosted_vcpu = i; break; } else if (yielded < 0) { try--; + kvm_inc_ple_window(); if (!try) break; } } } + if (!yielded) + kvm_inc_ple_window(); + kvm_vcpu_set_in_spin_loop(me, false); /* Ensure vcpu is not eligible during next spinloop */ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
