On Fri, 28 Feb 2020 11:15:02 -0500 Peter Xu <pet...@redhat.com> 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 <pbonz...@redhat.com> > Signed-off-by: Peter Xu <pet...@redhat.com> > --- > 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
