[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [PATCH v2 4/5] KVM: Kick resamplefd for split kernel irqchip
From: |
Alex Williamson |
Subject: |
Re: [PATCH v2 4/5] KVM: Kick resamplefd for split kernel irqchip |
Date: |
Mon, 9 Mar 2020 16:10:59 -0600 |
On Fri, 28 Feb 2020 11:15:02 -0500
Peter Xu <address@hidden> wrote:
> This is majorly only for X86 because that's the only one that supports
> split irqchip for now.
>
> When the irqchip is split, we face a dilemma that KVM irqfd will be
> enabled, however the slow irqchip is still running in the userspace.
> It means that the resamplefd in the kernel irqfds won't take any
> effect and it will miss to ack INTx interrupts on EOIs.
>
> One example is split irqchip with VFIO INTx, which will break if we
> use the VFIO INTx fast path.
>
> This patch can potentially supports the VFIO fast path again for INTx,
> that the IRQ delivery will still use the fast path, while we don't
> need to trap MMIOs in QEMU for the device to emulate the EIOs (see the
> callers of vfio_eoi() hook). However the EOI of the INTx will still
> need to be done from the userspace by caching all the resamplefds in
> QEMU and kick properly for IOAPIC EOI broadcast.
>
> This is tricky because in this case the userspace ioapic irr &
> remote-irr will be bypassed. However such a change will greatly boost
> performance for assigned devices using INTx irqs (TCP_RR boosts 46%
> after this patch applied).
>
> When the userspace is responsible for the resamplefd kickup, don't
> register it on the kvm_irqfd anymore, because on newer kernels (after
> commit 654f1f13ea56, 5.2+) the KVM_IRQFD will fail if with both split
> irqchip and resamplefd. This will make sure that the fast path will
> work for all supported kernels.
>
> https://patchwork.kernel.org/patch/10738541/#22609933
>
> Suggested-by: Paolo Bonzini <address@hidden>
> Signed-off-by: Peter Xu <address@hidden>
> ---
> accel/kvm/kvm-all.c | 85 +++++++++++++++++++++++++++++++++++++++++-
> accel/kvm/trace-events | 1 +
> hw/intc/ioapic.c | 23 +++++++++++-
> include/sysemu/kvm.h | 7 ++++
> 4 files changed, 112 insertions(+), 4 deletions(-)
>
> diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
> index d49b74512a..89771ea114 100644
> --- a/accel/kvm/kvm-all.c
> +++ b/accel/kvm/kvm-all.c
> @@ -159,9 +159,65 @@ static const KVMCapabilityInfo
> kvm_required_capabilites[] = {
> static NotifierList kvm_irqchip_change_notifiers =
> NOTIFIER_LIST_INITIALIZER(kvm_irqchip_change_notifiers);
>
> +struct KVMResampleFd {
> + int gsi;
> + EventNotifier *resample_event;
> + QLIST_ENTRY(KVMResampleFd) node;
> +};
> +typedef struct KVMResampleFd KVMResampleFd;
> +
> +/*
> + * Only used with split irqchip where we need to do the resample fd
> + * kick for the kernel from userspace.
> + */
> +static QLIST_HEAD(, KVMResampleFd) kvm_resample_fd_list =
> + QLIST_HEAD_INITIALIZER(kvm_resample_fd_list);
> +
> #define kvm_slots_lock(kml) qemu_mutex_lock(&(kml)->slots_lock)
> #define kvm_slots_unlock(kml) qemu_mutex_unlock(&(kml)->slots_lock)
>
> +static inline void kvm_resample_fd_remove(int gsi)
> +{
> + KVMResampleFd *rfd;
> +
> + QLIST_FOREACH(rfd, &kvm_resample_fd_list, node) {
> + if (rfd->gsi == gsi) {
> + QLIST_REMOVE(rfd, node);
> + g_free(rfd);
> + break;
> + }
> + }
> +}
> +
> +static inline void kvm_resample_fd_insert(int gsi, EventNotifier *event)
> +{
> + KVMResampleFd *rfd = g_new0(KVMResampleFd, 1);
> +
> + rfd->gsi = gsi;
> + rfd->resample_event = event;
> +
> + QLIST_INSERT_HEAD(&kvm_resample_fd_list, rfd, node);
> +}
> +
> +bool kvm_resample_fd_notify(int gsi)
> +{
> + KVMResampleFd *rfd;
> +
> + if (!kvm_irqchip_is_split()) {
> + return false;
> + }
> +
> + QLIST_FOREACH(rfd, &kvm_resample_fd_list, node) {
> + if (rfd->gsi == gsi) {
> + event_notifier_set(rfd->resample_event);
> + trace_kvm_resample_fd_notify(gsi);
> + return true;
> + }
> + }
> +
> + return false;
> +}
> +
> int kvm_get_max_memslots(void)
> {
> KVMState *s = KVM_STATE(current_accel());
[snip]
> diff --git a/hw/intc/ioapic.c b/hw/intc/ioapic.c
> index 15747fe2c2..13921b333d 100644
> --- a/hw/intc/ioapic.c
> +++ b/hw/intc/ioapic.c
> @@ -236,8 +236,27 @@ void ioapic_eoi_broadcast(int vector)
> for (n = 0; n < IOAPIC_NUM_PINS; n++) {
> entry = s->ioredtbl[n];
>
> - if ((entry & IOAPIC_VECTOR_MASK) != vector ||
> - ((entry >> IOAPIC_LVT_TRIGGER_MODE_SHIFT) & 1) !=
> IOAPIC_TRIGGER_LEVEL) {
> + if ((entry & IOAPIC_VECTOR_MASK) != vector) {
> + continue;
> + }
> +
> + /*
> + * When IOAPIC is in the userspace while APIC is still in
> + * the kernel (i.e., split irqchip), we have a trick to
> + * kick the resamplefd logic for registered irqfds from
> + * userspace to deactivate the IRQ. When that happens, it
> + * means the irq bypassed userspace IOAPIC (so the irr and
> + * remote-irr of the table entry should be bypassed too
> + * even if interrupt come), then we don't need to clear
> + * the remote-IRR and check irr again because they'll
> + * always be zeros.
> + */
> + if (kvm_resample_fd_notify(n)) {
> + continue;
> + }
It seems the problem I reported is here. In my configuration virtio-blk
and an assigned e1000e share an interrupt. virtio-blk is initializing
and apparently triggers an interrupt. The vfio-pci device is
configured for INTx though not active yet, but kvm_resample_fd_notify()
kicks the fd here, so we continue. If I remove the continue here both
devices seem to work, but I don't claim to understand the condition
we're trying to continue for here yet. This series needs more testing
with shared interrupts. Thanks,
Alex