Re: [Qemu-devel] [RFC PATCH 5/5] vfio/quirks: Enable ioeventfd quirks to be handled by vfio directly

[Auger Eric <eric.auger@redhat.com>]

Hi Alex,
On 07/02/18 01:26, Alex Williamson wrote:
> With vfio ioeventfd support, we can program vfio-pci to perform a
> specified BAR write when an eventfd is triggered.  This allows the
> KVM ioeventfd to be wired directly to vfio-pci, entirely avoiding
> userspace handling for these events.  On the same micro-benchmark
> where the ioeventfd got us to almost 90% of performance versus
> disabling the GeForce quirks, this gets us to within 95%.
> 
> Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
> ---
>  hw/vfio/pci-quirks.c |   42 ++++++++++++++++++++++++++++++++++++------
>  1 file changed, 36 insertions(+), 6 deletions(-)
> 
> diff --git a/hw/vfio/pci-quirks.c b/hw/vfio/pci-quirks.c
> index e739efe601b1..35a4d5197e2d 100644
> --- a/hw/vfio/pci-quirks.c
> +++ b/hw/vfio/pci-quirks.c
> @@ -16,6 +16,7 @@
>  #include "qemu/range.h"
>  #include "qapi/error.h"
>  #include "qapi/visitor.h"
> +#include <sys/ioctl.h>
>  #include "hw/nvram/fw_cfg.h"
>  #include "pci.h"
>  #include "trace.h"
> @@ -287,13 +288,27 @@ static VFIOQuirk *vfio_quirk_alloc(int nr_mem)
>      return quirk;
>  }
>  
> -static void vfio_ioeventfd_exit(VFIOIOEventFD *ioeventfd)
> +static void vfio_ioeventfd_exit(VFIOPCIDevice *vdev, VFIOIOEventFD *ioeventfd)
>  {
> +    struct vfio_device_ioeventfd vfio_ioeventfd;
> +
>      QLIST_REMOVE(ioeventfd, next);
> +
>      memory_region_del_eventfd(ioeventfd->mr, ioeventfd->addr, ioeventfd->size,
>                                ioeventfd->match_data, ioeventfd->data,
>                                &ioeventfd->e);
> +
>      qemu_set_fd_handler(event_notifier_get_fd(&ioeventfd->e), NULL, NULL, NULL);
> +
> +    vfio_ioeventfd.argsz = sizeof(vfio_ioeventfd);
> +    vfio_ioeventfd.flags = ioeventfd->size;
> +    vfio_ioeventfd.data = ioeventfd->data;
> +    vfio_ioeventfd.offset = ioeventfd->region->fd_offset +
> +                            ioeventfd->region_addr;
> +    vfio_ioeventfd.fd = -1;
> +
> +    ioctl(vdev->vbasedev.fd, VFIO_DEVICE_IOEVENTFD, &vfio_ioeventfd);
> +
>      event_notifier_cleanup(&ioeventfd->e);
>      g_free(ioeventfd);
>  }
> @@ -315,6 +330,8 @@ static VFIOIOEventFD *vfio_ioeventfd_init(VFIOPCIDevice *vdev,
>                                            hwaddr region_addr)
>  {
>      VFIOIOEventFD *ioeventfd = g_malloc0(sizeof(*ioeventfd));
> +    struct vfio_device_ioeventfd vfio_ioeventfd;
> +    char vfio_enabled = '+';
>  
>      if (event_notifier_init(&ioeventfd->e, 0)) {
>          g_free(ioeventfd);
> @@ -329,15 +346,28 @@ static VFIOIOEventFD *vfio_ioeventfd_init(VFIOPCIDevice *vdev,
>      ioeventfd->region = region;
>      ioeventfd->region_addr = region_addr;
>  
> -    qemu_set_fd_handler(event_notifier_get_fd(&ioeventfd->e),
> -                        vfio_ioeventfd_handler, NULL, ioeventfd);
> +    vfio_ioeventfd.argsz = sizeof(vfio_ioeventfd);
> +    vfio_ioeventfd.flags = ioeventfd->size;
> +    vfio_ioeventfd.data = ioeventfd->data;
> +    vfio_ioeventfd.offset = ioeventfd->region->fd_offset +
> +                            ioeventfd->region_addr;
> +    vfio_ioeventfd.fd = event_notifier_get_fd(&ioeventfd->e);
> +
> +    if (ioctl(vdev->vbasedev.fd,
> +              VFIO_DEVICE_IOEVENTFD, &vfio_ioeventfd) != 0) {
> +        qemu_set_fd_handler(event_notifier_get_fd(&ioeventfd->e),
> +                            vfio_ioeventfd_handler, NULL, ioeventfd);
> +        vfio_enabled = '-';
> +    }
> +
>      memory_region_add_eventfd(ioeventfd->mr, ioeventfd->addr,
>                                ioeventfd->size, ioeventfd->match_data,
>                                ioeventfd->data, &ioeventfd->e);
>  
>      info_report("Enabled automatic ioeventfd acceleration for %s region %d, "
> -                "offset 0x%"HWADDR_PRIx", data 0x%"PRIx64", size %u",
> -                vdev->vbasedev.name, region->nr, region_addr, data, size);
> +                "offset 0x%"HWADDR_PRIx", data 0x%"PRIx64", size %u, vfio%c",
> +                vdev->vbasedev.name, region->nr, region_addr, data, size,
> +                vfio_enabled);
Not sure if this message is really helpful for the end-user to
understand what happens. Maybe adding a trace event when everything
happens as it should and an error_report if we failed setting up the
vfio kernel handler, explaining the sub-optimal performance that can result.

Thanks

Eric
>  
>      return ioeventfd;
>  }
> @@ -1767,7 +1797,7 @@ void vfio_bar_quirk_exit(VFIOPCIDevice *vdev, int nr)
>  
>      QLIST_FOREACH(quirk, &bar->quirks, next) {
>          while (!QLIST_EMPTY(&quirk->ioeventfds)) {
> -            vfio_ioeventfd_exit(QLIST_FIRST(&quirk->ioeventfds));
> +            vfio_ioeventfd_exit(vdev, QLIST_FIRST(&quirk->ioeventfds));
>          }
>  
>          for (i = 0; i < quirk->nr_mem; i++) {
>