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Message-ID: <20120119143032.GC5294@redhat.com>
Date: Thu, 19 Jan 2012 16:30:33 +0200
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Jan Kiszka <jan.kiszka@...mens.com>
Cc: Alex Williamson <alex.williamson@...hat.com>,
Avi Kivity <avi@...hat.com>,
Marcelo Tosatti <mtosatti@...hat.com>,
"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC] kvm: deliver msix interrupts from irq handler
On Thu, Jan 19, 2012 at 01:04:32PM +0100, Jan Kiszka wrote:
> On 2012-01-18 19:10, Michael S. Tsirkin wrote:
> > We can deliver certain interrupts, notably MSIX,
> > from atomic context. Add a new API kvm_set_irq_inatomic,
> > that does exactly that, and use it to implement
> > an irq handler for msi.
> >
> > This reduces the pressure on scheduler in case
> > where host and guest irq share a host cpu.
> >
> > Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
> >
> > Untested.
> > Note: this is on top of my host irq patch.
> > Probably needs to be rebased to be independent
> > and split up to new API + usage.
> >
> > ---
> > include/linux/kvm_host.h | 2 +
> > virt/kvm/assigned-dev.c | 31 +++++++++++++++++++++++++-
> > virt/kvm/irq_comm.c | 52 ++++++++++++++++++++++++++++++++++++++++++++++
> > 3 files changed, 83 insertions(+), 2 deletions(-)
> >
> > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> > index f0361bc..e2b89ea 100644
> > --- a/include/linux/kvm_host.h
> > +++ b/include/linux/kvm_host.h
> > @@ -548,6 +548,8 @@ void kvm_get_intr_delivery_bitmask(struct kvm_ioapic *ioapic,
> > #endif
> > int kvm_set_irq(struct kvm *kvm, int irq_source_id, u32 irq, int level,
> > int host_irq);
> > +int kvm_set_irq_inatomic(struct kvm *kvm, int irq_source_id, u32 irq, int level,
> > + int host_irq);
> > int kvm_set_msi(struct kvm_kernel_irq_routing_entry *irq_entry, struct kvm *kvm,
> > int irq_source_id, int level, int host_irq);
> > void kvm_notify_acked_irq(struct kvm *kvm, unsigned irqchip, unsigned pin);
> > diff --git a/virt/kvm/assigned-dev.c b/virt/kvm/assigned-dev.c
> > index cc4bb7a..73bb001 100644
> > --- a/virt/kvm/assigned-dev.c
> > +++ b/virt/kvm/assigned-dev.c
> > @@ -57,6 +57,14 @@ static int find_index_from_host_irq(struct kvm_assigned_dev_kernel
> > return index;
> > }
> >
> > +static irqreturn_t kvm_assigned_dev_msi(int irq, void *dev_id)
> > +{
> > + int ret = kvm_set_irq_inatomic(assigned_dev->kvm,
> > + assigned_dev->irq_source_id,
> > + assigned_dev->guest_irq, 1, irq);
> > + return unlikely(ret == -EWOULDBLOCK) ? IRQ_WAKE_THREAD : IRQ_HANDLED;
> > +}
>
> This function gets unused (in theory) if !__KVM_HAVE_MSIX &&
> !__KVM_HAVE_MSI. Should be fixed for consistency reasons.
Does kvm still build with this !__KVM_HAVE_MSI? It does not look like
it would ...
> > +
> > static irqreturn_t kvm_assigned_dev_thread(int irq, void *dev_id)
> > {
> > struct kvm_assigned_dev_kernel *assigned_dev = dev_id;
> > @@ -75,6 +83,23 @@ static irqreturn_t kvm_assigned_dev_thread(int irq, void *dev_id)
> > }
> >
> > #ifdef __KVM_HAVE_MSIX
> > +static irqreturn_t kvm_assigned_dev_msix(int irq, void *dev_id)
> > +{
> > + struct kvm_assigned_dev_kernel *assigned_dev = dev_id;
> > + int index = find_index_from_host_irq(assigned_dev, irq);
> > + u32 vector;
> > + int ret = 0;
> > +
> > + if (index >= 0) {
> > + vector = assigned_dev->guest_msix_entries[index].vector;
> > + ret = kvm_set_irq_inatomic(assigned_dev->kvm,
> > + assigned_dev->irq_source_id,
> > + vector, 1, irq);
> > + }
> > +
> > + return unlikely(ret == -EWOULDBLOCK) ? IRQ_WAKE_THREAD : IRQ_HANDLED;
> > +}
> > +
> > static irqreturn_t kvm_assigned_dev_thread_msix(int irq, void *dev_id)
> > {
> > struct kvm_assigned_dev_kernel *assigned_dev = dev_id;
> > @@ -266,7 +291,8 @@ static int assigned_device_enable_host_msi(struct kvm *kvm,
> > }
> >
> > dev->host_irq = dev->dev->irq;
> > - if (request_threaded_irq(dev->host_irq, NULL, kvm_assigned_dev_thread,
> > + if (request_threaded_irq(dev->host_irq, kvm_assigned_dev_msi,
> > + kvm_assigned_dev_thread,
> > 0, dev->irq_name, dev)) {
> > pci_disable_msi(dev->dev);
> > return -EIO;
> > @@ -293,7 +319,8 @@ static int assigned_device_enable_host_msix(struct kvm *kvm,
> >
> > for (i = 0; i < dev->entries_nr; i++) {
> > r = request_threaded_irq(dev->host_msix_entries[i].vector,
> > - NULL, kvm_assigned_dev_thread_msix,
> > + kvm_assigned_dev_msix,
> > + kvm_assigned_dev_thread_msix,
> > 0, dev->irq_name, dev);
> > if (r)
> > goto err;
> > diff --git a/virt/kvm/irq_comm.c b/virt/kvm/irq_comm.c
> > index ba892df..68cd127 100644
> > --- a/virt/kvm/irq_comm.c
> > +++ b/virt/kvm/irq_comm.c
> > @@ -201,6 +201,58 @@ int kvm_set_irq(struct kvm *kvm, int irq_source_id, u32 irq, int level,
> > return ret;
> > }
> >
> > +static inline struct kvm_kernel_irq_routing_entry *
> > +kvm_get_entry(struct kvm *kvm, struct kvm_irq_routing_table *irq_rq, u32 irq)
> > +{
> > + struct kvm_kernel_irq_routing_entry *e;
> > + if (likely(irq < irq_rt->nr_rt_entries))
> > + hlist_for_each_entry(e, n, &irq_rt->map[irq], link)
> > + if (e->type == KVM_IRQ_ROUTING_MSI)
> > + return e;
> > + else
> > + return ERR_PTR(-EWOULDBLOCK);
> > + return ERR_PTR(-EINVAL);
> > +}
> > +
> > +/*
> > + * Deliver an IRQ in an atomic context if we can, or return a failure,
> > + * user can retry in a process context.
> > + * Return value:
> > + * -EWOULDBLOCK Can't deliver in atomic context
> > + * < 0 Interrupt was ignored (masked or not delivered for other reasons)
> > + * = 0 Interrupt was coalesced (previous irq is still pending)
> > + * > 0 Number of CPUs interrupt was delivered to
>
> Where do you make use of =0 vs. >0? Not in this patch at least. Do you
> consider using it for the APIC timer as well?
I think it might be handy in the future. It's an internal function
(not exported) so I just return what I get without worrying about it
too much: I didn't need to add code to get this :)
> > + */
> > +int kvm_set_irq_inatomic(struct kvm *kvm, int irq_source_id, u32 irq, int level,
> > + int host_irq)
> > +{
> > + struct kvm_kernel_irq_routing_entry *e;
> > + int ret = -EINVAL;
> > + struct kvm_irq_routing_table *irq_rt;
> > + struct hlist_node *n;
> > +
> > + trace_kvm_set_irq(irq, level, irq_source_id);
> > +
> > + /*
> > + * We know MSI are safe in interrupt context. They are also
> > + * easy as there's a single routing entry for these GSIs.
> > + * So only handle MSI in an atomic context, for now.
> > + */
> > + rcu_read_lock_bh();
> > + irq_rt = rcu_dereference(kvm->irq_routing);
> > + if (irq < irq_rt->nr_rt_entries)
> > + hlist_for_each_entry(e, n, &irq_rt->map[irq], link) {
> > + if (ei->type == KVM_IRQ_ROUTING_MSI)
> > + ret = kvm_set_msi(e, kvm, irq_source_id, level,
> > + host_irq);
> > + else
> > + ret = -EWOULDBLOCK;
> > + break;
> > + }
> > + rcu_read_unlock_bh();
> > + return ret;
> > +}
> > +
> > void kvm_notify_acked_irq(struct kvm *kvm, unsigned irqchip, unsigned pin)
> > {
> > struct kvm_irq_ack_notifier *kian;
>
> Highly welcome feature!
>
> Jan
I think we need to fix MSIX masking now, otherwise delivering interrupt
faster might get us a storm of interrupts.
> --
> Siemens AG, Corporate Technology, CT T DE IT 1
> Corporate Competence Center Embedded Linux
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