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Date: Thu, 12 Jan 2012 14:37:35 +0200
From: Avi Kivity <avi@...hat.com>
To: Liu Ping Fan <kernelfans@...il.com>
CC: kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
aliguori@...ibm.com, gleb@...hat.com, mtosatti@...hat.com,
xiaoguangrong.eric@...il.com, jan.kiszka@....de,
yoshikawa.takuya@....ntt.co.jp, Rik van Riel <riel@...hat.com>
Subject: Re: [PATCH v7] kvm: make vcpu life cycle separated from kvm instance
On 01/07/2012 04:55 AM, Liu Ping Fan wrote:
> From: Liu Ping Fan <pingfank@...ux.vnet.ibm.com>
>
> Currently, vcpu will be destructed only after kvm instance is
> destroyed. This result to vcpu keep idle in kernel, but can not
> be freed when it is unplugged in guest.
>
> Change this to vcpu's destruction before kvm instance, so vcpu MUST
Must?
> and CAN be destroyed before kvm instance. By this way, we can remove
> vcpu when guest does not need it any longer.
>
> TODO: push changes to other archs besides x86.
>
> -Rename kvm_vcpu_zap to kvm_vcpu_destruct and so on.
kvm_vcpu_destroy.
>
> struct kvm_vcpu {
> struct kvm *kvm;
> + struct list_head list;
vcpu_list_link, so it's clear this is not a head but a link, and so we
know which list it belongs to.
> - struct kvm_vcpu *vcpus[KVM_MAX_VCPUS];
> + struct list_head vcpus;
This has the potential for a slight performance regression by bouncing
an extra cache line, but it's acceptable IMO. We can always introduce
an apic ID -> vcpu hash table which improves things all around.
> |
> @@ -1593,11 +1598,9 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *me)
> {
> struct kvm *kvm = me->kvm;
> struct kvm_vcpu *vcpu;
> - int last_boosted_vcpu = me->kvm->last_boosted_vcpu;
> - int yielded = 0;
> - int pass;
> - int i;
> -
> + struct task_struct *task = NULL;
> + struct pid *pid;
> + int pass, firststart, lastone, yielded, idx;
Avoid unrelated changes please.
> @@ -1605,15 +1608,26 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *me)
> * VCPU is holding the lock that we need and will release it.
> * We approximate round-robin by starting at the last boosted VCPU.
> */
> - for (pass = 0; pass < 2 && !yielded; pass++) {
> - kvm_for_each_vcpu(i, vcpu, kvm) {
> - struct task_struct *task = NULL;
> - struct pid *pid;
> - if (!pass && i < last_boosted_vcpu) {
> - i = last_boosted_vcpu;
> + for (pass = 0, firststart = 0; pass < 2 && !yielded; pass++) {
> +
> + idx = srcu_read_lock(&kvm->srcu);
Can move the lock to the top level.
> + kvm_for_each_vcpu(vcpu, kvm) {
> + if (kvm->last_boosted_vcpu_id < 0 && !pass) {
> + pass = 1;
> + break;
> + }
> + if (!pass && !firststart &&
> + vcpu->vcpu_id != kvm->last_boosted_vcpu_id) {
> + continue;
> + } else if (!pass && !firststart) {
> + firststart = 1;
> continue;
> - } else if (pass && i > last_boosted_vcpu)
> + } else if (pass && !lastone) {
> + if (vcpu->vcpu_id == kvm->last_boosted_vcpu_id)
> + lastone = 1;
> + } else if (pass && lastone)
> break;
> +
Seems like a large change. Is this because the vcpu list is unordered?
Maybe it's better to order it.
Rik?
> if (vcpu == me)
> continue;
> if (waitqueue_active(&vcpu->wq))
> @@ -1629,15 +1643,20 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *me)
> put_task_struct(task);
> continue;
> }
> +
> if (yield_to(task, 1)) {
> put_task_struct(task);
> - kvm->last_boosted_vcpu = i;
> + mutex_lock(&kvm->lock);
> + kvm->last_boosted_vcpu_id = vcpu->vcpu_id;
> + mutex_unlock(&kvm->lock);
Why take the mutex?
> @@ -1673,11 +1692,30 @@ static int kvm_vcpu_mmap(struct file *file, struct vm_area_struct *vma)
> return 0;
> }
>
> +static void kvm_vcpu_destruct(struct kvm_vcpu *vcpu)
> +{
> + kvm_arch_vcpu_destruct(vcpu);
> +}
> +
> static int kvm_vcpu_release(struct inode *inode, struct file *filp)
> {
> struct kvm_vcpu *vcpu = filp->private_data;
> + struct kvm *kvm = vcpu->kvm;
> + filp->private_data = NULL;
> +
> + mutex_lock(&kvm->lock);
> + list_del_rcu(&vcpu->list);
> + atomic_dec(&kvm->online_vcpus);
> + mutex_unlock(&kvm->lock);
> + synchronize_srcu_expedited(&kvm->srcu);
Why _expedited?
Even better would be call_srcu() but it doesn't exist.
I think we can actually use regular rcu. The only user that blocks is
kvm_vcpu_on_spin(), yes? so we can convert the vcpu to a task using
get_pid_task(), then, outside the rcu lock, call yield_to().
>
> - kvm_put_kvm(vcpu->kvm);
> + mutex_lock(&kvm->lock);
> + if (kvm->last_boosted_vcpu_id == vcpu->vcpu_id)
> + kvm->last_boosted_vcpu_id = -1;
> + mutex_unlock(&kvm->lock);
> +
> + /*vcpu is out of list,drop it safely*/
> + kvm_vcpu_destruct(vcpu);
Can all kvm_arch_vcpu_destroy() directly.
> +static struct kvm_vcpu *kvm_vcpu_create(struct kvm *kvm, u32 id)
> +{
> + struct kvm_vcpu *vcpu;
> + vcpu = kvm_arch_vcpu_create(kvm, id);
> + if (IS_ERR(vcpu))
> + return vcpu;
> + INIT_LIST_HEAD(&vcpu->list);
Really needed?
> + return vcpu;
> +}
Just fold this into the caller.
> +
> /*
> * Creates some virtual cpus. Good luck creating more than one.
> */
> static int kvm_vm_ioctl_create_vcpu(struct kvm *kvm, u32 id)
> {
> - int r;
> + int r, idx;
> struct kvm_vcpu *vcpu, *v;
>
> - vcpu = kvm_arch_vcpu_create(kvm, id);
> + vcpu = kvm_vcpu_create(kvm, id);
> if (IS_ERR(vcpu))
> return PTR_ERR(vcpu);
>
> @@ -1723,13 +1771,15 @@ static int kvm_vm_ioctl_create_vcpu(struct kvm *kvm, u32 id)
> goto unlock_vcpu_destroy;
> }
>
> - kvm_for_each_vcpu(r, v, kvm)
> + idx = srcu_read_lock(&kvm->srcu);
> + kvm_for_each_vcpu(v, kvm) {
> if (v->vcpu_id == id) {
> r = -EEXIST;
> + srcu_read_unlock(&kvm->srcu, idx);
Put that in the error path please (add a new label if needed).
> goto unlock_vcpu_destroy;
>
> - kvm->vcpus[atomic_read(&kvm->online_vcpus)] = vcpu;
> - smp_wmb();
> + /*Protected by kvm->lock*/
Spaces.
> + list_add_rcu(&vcpu->list, &kvm->vcpus);
> atomic_inc(&kvm->online_vcpus);
--
error compiling committee.c: too many arguments to function
--
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