On Tue, 17 Mar 2020 18:49:23 -0400 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> > --- > v3.1 changelog > - only kick resamplefd for level triggered irqs [Alex] > accel/kvm/kvm-all.c | 79 ++++++++++++++++++++++++++++++++++++++++-- > accel/kvm/trace-events | 1 + > hw/intc/ioapic.c | 17 +++++++++ > include/sysemu/kvm.h | 4 +++ > 4 files changed, 99 insertions(+), 2 deletions(-) Reviewed-by: Alex Williamson <alex.william...@redhat.com> > diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c > index d49b74512a..9a85fd1b8f 100644 > --- a/accel/kvm/kvm-all.c > +++ b/accel/kvm/kvm-all.c > @@ -159,9 +159,59 @@ 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); > +} > + > +void kvm_resample_fd_notify(int gsi) > +{ > + KVMResampleFd *rfd; > + > + 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; > + } > + } > +} > + > int kvm_get_max_memslots(void) > { > KVMState *s = KVM_STATE(current_accel()); > @@ -1642,8 +1692,33 @@ static int kvm_irqchip_assign_irqfd(KVMState *s, > EventNotifier *event, > }; > > if (rfd != -1) { > - irqfd.flags |= KVM_IRQFD_FLAG_RESAMPLE; > - irqfd.resamplefd = rfd; > + assert(assign); > + if (kvm_irqchip_is_split()) { > + /* > + * When the slow irqchip (e.g. IOAPIC) is in the > + * userspace, KVM kernel resamplefd will not work because > + * the EOI of the interrupt will be delivered to userspace > + * instead, so the KVM kernel resamplefd kick will be > + * skipped. The userspace here mimics what the kernel > + * provides with resamplefd, remember the resamplefd and > + * kick it when we receive EOI of this IRQ. > + * > + * This is hackery because IOAPIC is mostly bypassed > + * (except EOI broadcasts) when irqfd is used. However > + * this can bring much performance back for split irqchip > + * with INTx IRQs (for VFIO, this gives 93% perf of the > + * full fast path, which is 46% perf boost comparing to > + * the INTx slow path). > + */ > + kvm_resample_fd_insert(virq, resample); > + } else { > + irqfd.flags |= KVM_IRQFD_FLAG_RESAMPLE; > + irqfd.resamplefd = rfd; > + } > + } else if (!assign) { > + if (kvm_irqchip_is_split()) { > + kvm_resample_fd_remove(virq); > + } > } > > if (!kvm_irqfds_enabled()) { > diff --git a/accel/kvm/trace-events b/accel/kvm/trace-events > index 4fb6e59d19..a68eb66534 100644 > --- a/accel/kvm/trace-events > +++ b/accel/kvm/trace-events > @@ -16,4 +16,5 @@ kvm_set_ioeventfd_mmio(int fd, uint64_t addr, uint32_t val, > bool assign, uint32_ > kvm_set_ioeventfd_pio(int fd, uint16_t addr, uint32_t val, bool assign, > uint32_t size, bool datamatch) "fd: %d @0x%x val=0x%x assign: %d size: %d > match: %d" > kvm_set_user_memory(uint32_t slot, uint32_t flags, uint64_t guest_phys_addr, > uint64_t memory_size, uint64_t userspace_addr, int ret) "Slot#%d flags=0x%x > gpa=0x%"PRIx64 " size=0x%"PRIx64 " ua=0x%"PRIx64 " ret=%d" > kvm_clear_dirty_log(uint32_t slot, uint64_t start, uint32_t size) > "slot#%"PRId32" start 0x%"PRIx64" size 0x%"PRIx32 > +kvm_resample_fd_notify(int gsi) "gsi %d" > > diff --git a/hw/intc/ioapic.c b/hw/intc/ioapic.c > index 15747fe2c2..2ae96e10be 100644 > --- a/hw/intc/ioapic.c > +++ b/hw/intc/ioapic.c > @@ -241,6 +241,23 @@ void ioapic_eoi_broadcast(int 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). Still kick the resamplefds if > + * they're bound to the IRQ, to make sure to EOI the > + * interrupt for the hardware correctly. > + * > + * Note: We still need to go through the irr & remote-irr > + * operations below because we don't know whether there're > + * emulated devices that are using/sharing the same IRQ. > + */ > + kvm_resample_fd_notify(n); > + > if (!(entry & IOAPIC_LVT_REMOTE_IRR)) { > continue; > } > diff --git a/include/sysemu/kvm.h b/include/sysemu/kvm.h > index 141342de98..583a976f8a 100644 > --- a/include/sysemu/kvm.h > +++ b/include/sysemu/kvm.h > @@ -555,4 +555,8 @@ int kvm_set_one_reg(CPUState *cs, uint64_t id, void > *source); > int kvm_get_one_reg(CPUState *cs, uint64_t id, void *target); > struct ppc_radix_page_info *kvm_get_radix_page_info(void); > int kvm_get_max_memslots(void); > + > +/* Notify resamplefd for EOI of specific interrupts. */ > +void kvm_resample_fd_notify(int gsi); > + > #endif
