Re: [PATCH v2 1/2] KVM: x86: Use vector-hashing to deliver lowest-priority interrupts

From: Yang Zhang
Date: Sun Dec 20 2015 - 21:06:32 EST

On 2015/12/21 9:50, Wu, Feng wrote:


-----Original Message-----
From: Yang Zhang [mailto:yang.zhang.wz@xxxxxxxxx]
Sent: Monday, December 21, 2015 9:46 AM
To: Wu, Feng <feng.wu@xxxxxxxxx>; pbonzini@xxxxxxxxxx;
rkrcmar@xxxxxxxxxx
Cc: kvm@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
Subject: Re: [PATCH v2 1/2] KVM: x86: Use vector-hashing to deliver lowest-
priority interrupts

On 2015/12/16 9:37, Feng Wu wrote:
Use vector-hashing to deliver lowest-priority interrupts, As an
example, modern Intel CPUs in server platform use this method to
handle lowest-priority interrupts.

Signed-off-by: Feng Wu <feng.wu@xxxxxxxxx>
---
arch/x86/kvm/irq_comm.c | 27 ++++++++++++++++++-----
arch/x86/kvm/lapic.c | 57
++++++++++++++++++++++++++++++++++++++++---------
arch/x86/kvm/lapic.h | 2 ++
arch/x86/kvm/x86.c | 9 ++++++++
arch/x86/kvm/x86.h | 1 +
5 files changed, 81 insertions(+), 15 deletions(-)

diff --git a/arch/x86/kvm/irq_comm.c b/arch/x86/kvm/irq_comm.c
index 84b96d3..c8c5f61 100644
--- a/arch/x86/kvm/irq_comm.c
+++ b/arch/x86/kvm/irq_comm.c
@@ -32,6 +32,7 @@
#include "ioapic.h"

#include "lapic.h"
+#include "x86.h"

static int kvm_set_pic_irq(struct kvm_kernel_irq_routing_entry *e,
struct kvm *kvm, int irq_source_id, int level,
@@ -53,8 +54,10 @@ static int kvm_set_ioapic_irq(struct
kvm_kernel_irq_routing_entry *e,
int kvm_irq_delivery_to_apic(struct kvm *kvm, struct kvm_lapic *src,
struct kvm_lapic_irq *irq, unsigned long *dest_map)
{
- int i, r = -1;
+ int i, r = -1, idx = 0;
struct kvm_vcpu *vcpu, *lowest = NULL;
+ unsigned long dest_vcpu_bitmap[BITS_TO_LONGS(KVM_MAX_VCPUS)];
+ unsigned int dest_vcpus = 0;

if (irq->dest_mode == 0 && irq->dest_id == 0xff &&
kvm_lowest_prio_delivery(irq)) {
@@ -65,6 +68,8 @@ int kvm_irq_delivery_to_apic(struct kvm *kvm, struct
kvm_lapic *src,
if (kvm_irq_delivery_to_apic_fast(kvm, src, irq, &r, dest_map))
return r;

+ memset(dest_vcpu_bitmap, 0, sizeof(dest_vcpu_bitmap));
+
kvm_for_each_vcpu(i, vcpu, kvm) {
if (!kvm_apic_present(vcpu))
continue;
@@ -78,13 +83,25 @@ int kvm_irq_delivery_to_apic(struct kvm *kvm, struct
kvm_lapic *src,
r = 0;
r += kvm_apic_set_irq(vcpu, irq, dest_map);
} else if (kvm_lapic_enabled(vcpu)) {
- if (!lowest)
- lowest = vcpu;
- else if (kvm_apic_compare_prio(vcpu, lowest) < 0)
- lowest = vcpu;
+ if (!kvm_vector_hashing_enabled()) {
+ if (!lowest)
+ lowest = vcpu;
+ else if (kvm_apic_compare_prio(vcpu, lowest) <
0)
+ lowest = vcpu;
+ } else {
+ __set_bit(vcpu->vcpu_id, dest_vcpu_bitmap);
+ dest_vcpus++;
+ }
}
}

+ if (dest_vcpus != 0) {
+ idx = kvm_vector_2_index(irq->vector, dest_vcpus,
+ dest_vcpu_bitmap, KVM_MAX_VCPUS);
+
+ lowest = kvm_get_vcpu(kvm, idx - 1);
+ }
+
if (lowest)
r = kvm_apic_set_irq(lowest, irq, dest_map);

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index ecd4ea1..e29001f 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -678,6 +678,22 @@ bool kvm_apic_match_dest(struct kvm_vcpu *vcpu,
struct kvm_lapic *source,
}
}

+int kvm_vector_2_index(u32 vector, u32 dest_vcpus,
+ const unsigned long *bitmap, u32 bitmap_size)
+{
+ u32 mod;
+ int i, idx = 0;
+
+ mod = vector % dest_vcpus;
+
+ for (i = 0; i <= mod; i++) {
+ idx = find_next_bit(bitmap, bitmap_size, idx) + 1;
+ BUG_ON(idx > bitmap_size);
+ }
+
+ return idx;
+}
+
bool kvm_irq_delivery_to_apic_fast(struct kvm *kvm, struct kvm_lapic *src,
struct kvm_lapic_irq *irq, int *r, unsigned long *dest_map)
{
@@ -731,17 +747,38 @@ bool kvm_irq_delivery_to_apic_fast(struct kvm
*kvm, struct kvm_lapic *src,
dst = map->logical_map[cid];

if (kvm_lowest_prio_delivery(irq)) {
- int l = -1;
- for_each_set_bit(i, &bitmap, 16) {
- if (!dst[i])
- continue;
- if (l < 0)
- l = i;
- else if (kvm_apic_compare_prio(dst[i]->vcpu,
dst[l]->vcpu) < 0)
- l = i;
+ if (!kvm_vector_hashing_enabled()) {
+ int l = -1;
+ for_each_set_bit(i, &bitmap, 16) {
+ if (!dst[i])
+ continue;
+ if (l < 0)
+ l = i;
+ else if (kvm_apic_compare_prio(dst[i]-
vcpu, dst[l]->vcpu) < 0)
+ l = i;
+ }
+ bitmap = (l >= 0) ? 1 << l : 0;
+ } else {
+ int idx = 0;
+ unsigned int dest_vcpus = 0;
+
+ for_each_set_bit(i, &bitmap, 16) {
+ if (!dst[i]
&& !kvm_lapic_enabled(dst[i]->vcpu)) {

It should be or(||) not and (&&).

Oh, you are right! My negligence! Thanks for pointing this out, Yang!

btw, i think the kvm_lapic_enabled check is wrong here? Why need it here?


Thanks,
Feng



--
best regards
yang
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