Re: [Qemu-devel] [RESEND PATCH v16 6/6] hw/vfio/platform: add irqfd support

[Eric Auger <eric.auger@linaro.org>]

On 06/26/2015 01:57 PM, Peter Maydell wrote:
> On 15 June 2015 at 17:33, Eric Auger <eric.auger@linaro.org> wrote:
>> 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 Bennée <alex.bennee@linaro.org>
>> Tested-by: Vikram Sethi <vikrams@codeaurora.org>
>>
>> ---
>> v15 -> v16:
>> - add Vikram's T-b
>>
>> 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.
>> ---
>>  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 9382bb7..1d44085 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");
> 
> This error message seems rather cryptic; what is it trying to tell the user?
I acknowledge  ;-)
I will replace by "vfio: Unable to init event notifier for resampling"
> 
>> +        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;
> 
> Stray double-space.
ok
> 
>> +            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 */
> 
> This comment could probably be phrased more informatively :-)
sure
> 
>> +    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)
>> @@ -548,6 +646,7 @@ 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;
>> @@ -555,6 +654,13 @@ 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
> 
> You shouldn't need this CONFIG_KVM ifdef -- we deliberately provide
> "always false" versions of functions like kvm_irqfds_enabled() in
> sysemu/kvm.h so that we can avoid littering code with ifdefs.
> 
> It looks like your commit f41389ae3c54b failed to provide the
> non-KVM version of kvm_resamplefds_enabled(), but the correct
> fix is to provide it...
OK I ignored that. I will add kvm_resamplefds_allowed in kvm-stub.c then.
> 
> This implies removing the ifdefs earlier around vfio_start_irqfd_injection,
> but that should be OK -- we provide stub versions of functions like
> kvm_irqchip_add_irqfd_notifier() so the non-KVM code can still compile.

OK will try this out.

So this answers my previous question. Will send a v17

Thanks

Eric
> 
>> +
>>      trace_vfio_platform_realize(vbasedev->name, vdev->compat);
>>
>>      ret = vfio_base_device_init(vbasedev);
>> @@ -584,6 +690,7 @@ 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 6060d36..4390381 100644
>> --- a/trace-events
>> +++ b/trace-events
>> @@ -1594,6 +1594,7 @@ 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
>>
> 
> thanks
> -- PMM
>