[PATCH v15 10/10] hw/vfio/platform: add irqfd support

Eric Auger
2015-04-30T12:41:10Z

This patch aims at optimizing IRQ handling using irqfd framework.

Instead of handling the eventfds on user-side they are handled on
kernel side using
- the KVM irqfd framework,
- the VFIO driver virqfd framework.

the virtual IRQ completion is trapped at interrupt controller
This removes the need for fast/slow path swap.

Overall this brings significant performance improvements.

Signed-off-by: Alvise Rigo <a.rigo@virtualopensystems.com>
Signed-off-by: Eric Auger <eric.auger@linaro.org>
Reviewed-by: Alex Bennee<alex.bennee@linaro.org>

---
v13 -> v14:
- use connect_irq_notifier
- remove trace_vfio_platform_start_eventfd

v12 -> v13:
- setup the new mechanism for starting irqfd, based on
LinkPropertySetter override
- use kvm_irqchip_[add,remove]_irqfd_notifier new functions: no need
to bother about gsi (hence virtualID could be removed with small
change in trace-events)

v10 -> v11:
- Add Alex' Reviewed-by
- introduce kvm_accel in this patch and initialize it

v5 -> v6
- rely on kvm_irqfds_enabled() and kvm_resamplefds_enabled()
- guard KVM code with #ifdef CONFIG_KVM

v3 -> v4:
[Alvise Rigo]
Use of VFIO Platform driver v6 unmask/virqfd feature and removal
of resamplefd handler. Physical IRQ unmasking is now done in
VFIO driver.

v3:
[Eric Auger]
initial support with resamplefd handled on QEMU side since the
unmask was not supported on VFIO platform driver v5.

Conflicts:
hw/vfio/platform.c
---
hw/vfio/platform.c | 107 ++++++++++++++++++++++++++++++++++++++++
include/hw/vfio/vfio-platform.h | 2 +
trace-events | 1 +
3 files changed, 110 insertions(+)

diff --git a/hw/vfio/platform.c b/hw/vfio/platform.c
index 35266a8..901b98e 100644
--- a/hw/vfio/platform.c
+++ b/hw/vfio/platform.c
@@ -26,6 +26,7 @@
#include "hw/sysbus.h"
#include "trace.h"
#include "hw/platform-bus.h"
+#include "sysemu/kvm.h"

/*
* Functions used whatever the injection method
@@ -51,6 +52,7 @@ static VFIOINTp *vfio_init_intp(VFIODevice *vbasedev,
intp->pin = info.index;
intp->flags = info.flags;
intp->state = VFIO_IRQ_INACTIVE;
+ intp->kvm_accel = false;

sysbus_init_irq(sbdev, &intp->qemuirq);

@@ -61,6 +63,13 @@ static VFIOINTp *vfio_init_intp(VFIODevice *vbasedev,
error_report("vfio: Error: trigger event_notifier_init failed ");
return NULL;
}
+ /* Get an eventfd for resample/unmask */
+ ret = event_notifier_init(&intp->unmask, 0);
+ if (ret) {
+ g_free(intp);
+ error_report("vfio: Error: resample event_notifier_init failed eoi");
+ return NULL;
+ }

QLIST_INSERT_HEAD(&vdev->intp_list, intp, next);
return intp;
@@ -315,6 +324,95 @@ static int vfio_start_eventfd_injection(VFIOINTp *intp)
return ret;
}

+/*
+ * Functions used for irqfd
+ */
+
+#ifdef CONFIG_KVM
+
+/**
+ * vfio_set_resample_eventfd - sets the resamplefd for an IRQ
+ * @intp: the IRQ struct handle
+ * programs the VFIO driver to unmask this IRQ when the
+ * intp->unmask eventfd is triggered
+ */
+static int vfio_set_resample_eventfd(VFIOINTp *intp)
+{
+ VFIODevice *vbasedev = &intp->vdev->vbasedev;
+ struct vfio_irq_set *irq_set;
+ int argsz, ret;
+ int32_t *pfd;
+
+ argsz = sizeof(*irq_set) + sizeof(*pfd);
+ irq_set = g_malloc0(argsz);
+ irq_set->argsz = argsz;
+ irq_set->flags = VFIO_IRQ_SET_DATA_EVENTFD | VFIO_IRQ_SET_ACTION_UNMASK;
+ irq_set->index = intp->pin;
+ irq_set->start = 0;
+ irq_set->count = 1;
+ pfd = (int32_t *)&irq_set->data;
+ *pfd = event_notifier_get_fd(&intp->unmask);
+ qemu_set_fd_handler(*pfd, NULL, NULL, NULL);
+ ret = ioctl(vbasedev->fd, VFIO_DEVICE_SET_IRQS, irq_set);
+ g_free(irq_set);
+ if (ret < 0) {
+ error_report("vfio: Failed to set resample eventfd: %m");
+ }
+ return ret;
+}
+
+static void vfio_start_irqfd_injection(SysBusDevice *sbdev, qemu_irq irq)
+{
+ VFIOPlatformDevice *vdev = VFIO_PLATFORM_DEVICE(sbdev);
+ VFIOINTp *intp;
+ bool found = false;
+
+ QLIST_FOREACH(intp, &vdev->intp_list, next) {
+ if (intp->qemuirq == irq) {
+ found = true;
+ break;
+ }
+ }
+ assert(found);
+
+ /* Get to a known interrupt state */
+ qemu_set_fd_handler(event_notifier_get_fd(&intp->interrupt),
+ NULL, NULL, vdev);
+
+ vfio_mask_single_irqindex(&vdev->vbasedev, intp->pin);
+ qemu_set_irq(intp->qemuirq, 0);
+
+ if (kvm_irqchip_add_irqfd_notifier(kvm_state, &intp->interrupt,
+ &intp->unmask, irq) < 0) {
+ goto fail_irqfd;
+ }
+
+ if (vfio_set_trigger_eventfd(intp, NULL) < 0) {
+ goto fail_vfio;
+ }
+ if (vfio_set_resample_eventfd(intp) < 0) {
+ goto fail_vfio;
+ }
+
+ /* Let'em rip */
+ vfio_unmask_single_irqindex(&vdev->vbasedev, intp->pin);
+
+ intp->kvm_accel = true;
+
+ trace_vfio_platform_start_irqfd_injection(intp->pin,
+ event_notifier_get_fd(&intp->interrupt),
+ event_notifier_get_fd(&intp->unmask));
+ return;
+fail_vfio:
+ kvm_irqchip_remove_irqfd_notifier(kvm_state, &intp->interrupt, irq);
+fail_irqfd:
+ vfio_start_eventfd_injection(intp);
+ vfio_unmask_single_irqindex(&vdev->vbasedev, intp->pin);
+ return;
+}
+
+#endif /* CONFIG_KVM */
+
/* VFIO skeleton */

static void vfio_platform_compute_needs_reset(VFIODevice *vbasedev)
@@ -549,6 +647,7 @@ static void vfio_platform_realize(DeviceState *dev, Error **errp)
{
VFIOPlatformDevice *vdev = VFIO_PLATFORM_DEVICE(dev);
SysBusDevice *sbdev = SYS_BUS_DEVICE(dev);
+ SysBusDeviceClass *sbc = SYS_BUS_DEVICE_GET_CLASS(dev);
VFIODevice *vbasedev = &vdev->vbasedev;
VFIOINTp *intp;
int i, ret;
@@ -556,6 +655,13 @@ static void vfio_platform_realize(DeviceState *dev, Error **errp)
vbasedev->type = VFIO_DEVICE_TYPE_PLATFORM;
vbasedev->ops = &vfio_platform_ops;

+#ifdef CONFIG_KVM
+ if (kvm_irqfds_enabled() && kvm_resamplefds_enabled() &&
+ vdev->irqfd_allowed) {
+ sbc->connect_irq_notifier = vfio_start_irqfd_injection;
+ }
+#endif
+
trace_vfio_platform_realize(vbasedev->name, vdev->compat);

ret = vfio_base_device_init(vbasedev);
@@ -585,6 +691,7 @@ static Property vfio_platform_dev_properties[] = {
DEFINE_PROP_BOOL("x-mmap", VFIOPlatformDevice, vbasedev.allow_mmap, true),
DEFINE_PROP_UINT32("mmap-timeout-ms", VFIOPlatformDevice,
mmap_timeout, 1100),
+ DEFINE_PROP_BOOL("x-irqfd", VFIOPlatformDevice, irqfd_allowed, true),
DEFINE_PROP_END_OF_LIST(),
};

diff --git a/include/hw/vfio/vfio-platform.h b/include/hw/vfio/vfio-platform.h
index 26b2ad6..c5cf1d7 100644
--- a/include/hw/vfio/vfio-platform.h
+++ b/include/hw/vfio/vfio-platform.h
@@ -41,6 +41,7 @@ typedef struct VFIOINTp {
int state; /* inactive, pending, active */
uint8_t pin; /* index */
uint32_t flags; /* IRQ info flags */
+ bool kvm_accel; /* set when QEMU bypass through KVM enabled */
} VFIOINTp;

/* function type for user side eventfd handler */
@@ -57,6 +58,7 @@ typedef struct VFIOPlatformDevice {
uint32_t mmap_timeout; /* delay to re-enable mmaps after interrupt */
QEMUTimer *mmap_timer; /* allows fast-path resume after IRQ hit */
QemuMutex intp_mutex; /* protect the intp_list IRQ state */
+ bool irqfd_allowed; /* debug option to force irqfd on/off */
} VFIOPlatformDevice;

typedef struct VFIOPlatformDeviceClass {
diff --git a/trace-events b/trace-events
index ed8ed90..cb6381a 100644
--- a/trace-events
+++ b/trace-events
@@ -1571,6 +1571,7 @@ vfio_platform_intp_interrupt(int pin, int fd) "Inject IRQ #%d (fd = %d)"
vfio_platform_intp_inject_pending_lockheld(int pin, int fd) "Inject pending IRQ #%d (fd = %d)"
vfio_platform_populate_interrupts(int pin, int count, int flags) "- IRQ index %d: count %d, flags=0x%x"
vfio_intp_interrupt_set_pending(int index) "irq %d is set PENDING"
+vfio_platform_start_irqfd_injection(int index, int fd, int resamplefd) "IRQ index=%d, fd = %d, resamplefd = %d"

#hw/acpi/memory_hotplug.c
mhp_acpi_invalid_slot_selected(uint32_t slot) "0x%"PRIx32
--
1.8.3.2