linux-kernel - Re: [PATCH v4] kvm/irqchip: Speed up KVM_SET_GSI

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Date:	Mon, 2 Jun 2014 13:14:54 +0800
From:	hrg <hrgstephen@...il.com>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	Christian Borntraeger <borntraeger@...ibm.com>,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	Marcelo Tosatti <mtosatti@...hat.com>,
	"Michael S. Tsirkin" <mst@...hat.com>
Subject: Re: [PATCH v4] kvm/irqchip: Speed up KVM_SET_GSI_ROUTING

Hi,

I think you missed a cleanup_srcu_struct(&kvm->irq_srcu) in kvm_destroy_vm().

On Mon, May 5, 2014 at 10:26 PM, Paolo Bonzini <pbonzini@...hat.com> wrote:
> Il 05/05/2014 16:21, Christian Borntraeger ha scritto:
>
>> On 28/04/14 18:39, Paolo Bonzini wrote:
>>>
>>> From: Christian Borntraeger <borntraeger@...ibm.com>
>>
>>
>> Given all your work, What about From: Paolo Bonzini <pbonzini@...hat.com>
>> plus "Based on an inital patch from Christian Borntraeger"
>
>
> No big deal, I don't care about authorship that much.
>
>
>>> @@ -221,17 +225,18 @@ irqfd_wakeup(wait_queue_t *wait, unsigned mode, int
>>> sync, void *key)
>>>         unsigned long flags = (unsigned long)key;
>>>         struct kvm_kernel_irq_routing_entry *irq;
>>>         struct kvm *kvm = irqfd->kvm;
>>> +       int idx;
>>>
>>>         if (flags & POLLIN) {
>>> -               rcu_read_lock();
>>> -               irq = rcu_dereference(irqfd->irq_entry);
>>> +               idx = srcu_read_lock(&kvm->irq_srcu);
>>> +               irq = srcu_dereference(irqfd->irq_entry, &kvm->irq_srcu);
>>>                 /* An event has been signaled, inject an interrupt */
>>>                 if (irq)
>>>                         kvm_set_msi(irq, kvm,
>>> KVM_USERSPACE_IRQ_SOURCE_ID, 1,
>>>                                         false);
>>>                 else
>>>                         schedule_work(&irqfd->inject);
>>> -               rcu_read_unlock();
>>> +               srcu_read_unlock(&kvm->irq_srcu, idx);
>>>         }
>>>
>>>         if (flags & POLLHUP) {
>>> @@ -363,7 +368,7 @@ kvm_irqfd_assign(struct kvm *kvm, struct kvm_irqfd
>>> *args)
>>>                 }
>>>
>>>                 list_add_rcu(&irqfd->resampler_link,
>>> &irqfd->resampler->list);
>>> -               synchronize_rcu();
>>> +               synchronize_srcu(&kvm->irq_srcu);
>>
>>
>> No idea what resampler is, can this become time critical as well - iow do
>> we need expedited here?
>
>
> It's for level-triggered interrupts.  I decided that if synchronize_rcu was
> good enough before, synchronize_srcu will do after the patch.
>
>
>>> @@ -85,7 +86,7 @@ void kvm_unregister_irq_ack_notifier(struct kvm *kvm,
>>>         mutex_lock(&kvm->irq_lock);
>>>         hlist_del_init_rcu(&kian->link);
>>>         mutex_unlock(&kvm->irq_lock);
>>> -       synchronize_rcu();
>>> +       synchronize_srcu_expedited(&kvm->irq_srcu);
>>
>>
>> Hmm, looks like all callers are slow path (shutdown, deregister assigned
>> dev). Couldnt
>> we use the non expedited variant?
>
>
> ... but I have screwed up this one.  Thanks, I'll change it.
>
>
>>>         r = kvm_arch_init_vm(kvm, type);
>>>         if (r)
>>> -               goto out_err_nodisable;
>>> +               goto out_err_no_disable;
>>>
>>>         r = hardware_enable_all();
>>>         if (r)
>>> -               goto out_err_nodisable;
>>> +               goto out_err_no_disable;
>>>
>>>  #ifdef CONFIG_HAVE_KVM_IRQCHIP
>>>         INIT_HLIST_HEAD(&kvm->mask_notifier_list);
>>> @@ -473,10 +473,12 @@ static struct kvm *kvm_create_vm(unsigned long
>>> type)
>>>         r = -ENOMEM;
>>>         kvm->memslots = kzalloc(sizeof(struct kvm_memslots), GFP_KERNEL);
>>>         if (!kvm->memslots)
>>> -               goto out_err_nosrcu;
>>> +               goto out_err_no_srcu;
>>>         kvm_init_memslots_id(kvm);
>>>         if (init_srcu_struct(&kvm->srcu))
>>> -               goto out_err_nosrcu;
>>> +               goto out_err_no_srcu;
>>> +       if (init_srcu_struct(&kvm->irq_srcu))
>>> +               goto out_err_no_irq_srcu;
>>>         for (i = 0; i < KVM_NR_BUSES; i++) {
>>>                 kvm->buses[i] = kzalloc(sizeof(struct kvm_io_bus),
>>>                                         GFP_KERNEL);
>>> @@ -505,10 +507,12 @@ static struct kvm *kvm_create_vm(unsigned long
>>> type)
>>>         return kvm;
>>>
>>>  out_err:
>>> +       cleanup_srcu_struct(&kvm->irq_srcu);
>>> +out_err_no_irq_srcu:
>>>         cleanup_srcu_struct(&kvm->srcu);
>>> -out_err_nosrcu:
>>> +out_err_no_srcu:
>>>         hardware_disable_all();
>>> -out_err_nodisable:
>>> +out_err_no_disable:
>>
>>
>>
>> the patch would be smaller without this change, but it makes the naming
>> more consistent, so ok.
>
>
> Yeah, out_err_noirq_srcu or out_err_noirqsrcu are both very ugly.
>
> Thanks for the review, I'm making the small change to remove expedited and
> applying to kvm/queue.
>
> Paolo
>
>
>>
>>>         for (i = 0; i < KVM_NR_BUSES; i++)
>>>                 kfree(kvm->buses[i]);
>>>         kfree(kvm->memslots);
>>>
>>
>
> --
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