Re: [Qemu-devel] [PATCH] msix: Drop tracking of used vectors

[Michael S. Tsirkin]

On Thu, Jul 05, 2012 at 11:42:14AM +0200, Jan Kiszka wrote:
> This optimization was once used in qemu-kvm to keep KVM route usage low.
> But now we solved that problem via lazy updates.

What if we are using vhost which AFAIK can't use the lazy path?

> It also tried to handle
> the case of vectors shared between different sources of the same device.
> However, this never really worked

Interesting. Guests actually have support and it seems to work for me.
What's the issue?

> and will have to be addressed
> differently anyway.

what's the plan to address this?

> So drop this obsolete interface.
> 
> We still need interfaces to clear pending vectors though. Provide
> msix_clear_vector and msix_clear_all_vectors for this.
> 
> Signed-off-by: Jan Kiszka <address@hidden>

Looks like if guest tries to use too many vectors it will have to switch
to userspace virtio where previously we would report failure to guest
and it would configure less vectors, which seems better.

I'd like to understand whether this patch is a pre-requisite for
anything or just a cleanup?


> ---
>  hw/ivshmem.c    |   20 -------------------
>  hw/msix.c       |   57 ++++++++++++------------------------------------------
>  hw/msix.h       |    5 +--
>  hw/pci.h        |    2 -
>  hw/virtio-pci.c |   20 +++++++-----------
>  5 files changed, 23 insertions(+), 81 deletions(-)
> 
> diff --git a/hw/ivshmem.c b/hw/ivshmem.c
> index 7d4123c..9afc4a2 100644
> --- a/hw/ivshmem.c
> +++ b/hw/ivshmem.c
> @@ -508,28 +508,11 @@ static void ivshmem_read(void *opaque, const uint8_t * 
> buf, int flags)
>      return;
>  }
>  
> -/* Select the MSI-X vectors used by device.
> - * ivshmem maps events to vectors statically, so
> - * we just enable all vectors on init and after reset. */
> -static void ivshmem_use_msix(IVShmemState * s)
> -{
> -    int i;
> -
> -    if (!msix_present(&s->dev)) {
> -        return;
> -    }
> -
> -    for (i = 0; i < s->vectors; i++) {
> -        msix_vector_use(&s->dev, i);
> -    }
> -}
> -
>  static void ivshmem_reset(DeviceState *d)
>  {
>      IVShmemState *s = DO_UPCAST(IVShmemState, dev.qdev, d);
>  
>      s->intrstatus = 0;
> -    ivshmem_use_msix(s);
>      return;
>  }
>  
> @@ -571,8 +554,6 @@ static void ivshmem_setup_msi(IVShmemState * s)
>  
>      /* allocate QEMU char devices for receiving interrupts */
>      s->eventfd_table = g_malloc0(s->vectors * sizeof(EventfdEntry));
> -
> -    ivshmem_use_msix(s);
>  }
>  
>  static void ivshmem_save(QEMUFile* f, void *opaque)
> @@ -614,7 +595,6 @@ static int ivshmem_load(QEMUFile* f, void *opaque, int 
> version_id)
>  
>      if (ivshmem_has_feature(proxy, IVSHMEM_MSI)) {
>          msix_load(&proxy->dev, f);
> -     ivshmem_use_msix(proxy);
>      } else {
>          proxy->intrstatus = qemu_get_be32(f);
>          proxy->intrmask = qemu_get_be32(f);
> diff --git a/hw/msix.c b/hw/msix.c
> index fd9ea95..e38927c 100644
> --- a/hw/msix.c
> +++ b/hw/msix.c
> @@ -260,7 +260,6 @@ int msix_init(struct PCIDevice *dev, unsigned short 
> nentries,
>  
>      dev->msix_table = g_malloc0(table_size);
>      dev->msix_pba = g_malloc0(pba_size);
> -    dev->msix_entry_used = g_malloc0(nentries * sizeof 
> *dev->msix_entry_used);
>  
>      msix_mask_all(dev, nentries);
>  
> @@ -317,16 +316,6 @@ int msix_init_exclusive_bar(PCIDevice *dev, unsigned 
> short nentries,
>      return 0;
>  }
>  
> -static void msix_free_irq_entries(PCIDevice *dev)
> -{
> -    int vector;
> -
> -    for (vector = 0; vector < dev->msix_entries_nr; ++vector) {
> -        dev->msix_entry_used[vector] = 0;
> -        msix_clr_pending(dev, vector);
> -    }
> -}
> -
>  /* Clean up resources for the device. */
>  void msix_uninit(PCIDevice *dev, MemoryRegion *table_bar, MemoryRegion 
> *pba_bar)
>  {
> @@ -335,7 +324,6 @@ void msix_uninit(PCIDevice *dev, MemoryRegion *table_bar, 
> MemoryRegion *pba_bar)
>      }
>      pci_del_capability(dev, PCI_CAP_ID_MSIX, MSIX_CAP_LENGTH);
>      dev->msix_cap = 0;
> -    msix_free_irq_entries(dev);
>      dev->msix_entries_nr = 0;
>      memory_region_del_subregion(pba_bar, &dev->msix_pba_mmio);
>      memory_region_destroy(&dev->msix_pba_mmio);
> @@ -345,8 +333,6 @@ void msix_uninit(PCIDevice *dev, MemoryRegion *table_bar, 
> MemoryRegion *pba_bar)
>      memory_region_destroy(&dev->msix_table_mmio);
>      g_free(dev->msix_table);
>      dev->msix_table = NULL;
> -    g_free(dev->msix_entry_used);
> -    dev->msix_entry_used = NULL;
>      dev->cap_present &= ~QEMU_PCI_CAP_MSIX;
>      return;
>  }
> @@ -381,7 +367,6 @@ void msix_load(PCIDevice *dev, QEMUFile *f)
>          return;
>      }
>  
> -    msix_free_irq_entries(dev);
>      qemu_get_buffer(f, dev->msix_table, n * PCI_MSIX_ENTRY_SIZE);
>      qemu_get_buffer(f, dev->msix_pba, (n + 7) / 8);
>      msix_update_function_masked(dev);
> @@ -410,8 +395,9 @@ void msix_notify(PCIDevice *dev, unsigned vector)
>  {
>      MSIMessage msg;
>  
> -    if (vector >= dev->msix_entries_nr || !dev->msix_entry_used[vector])
> +    if (vector >= dev->msix_entries_nr) {
>          return;
> +    }
>      if (msix_is_masked(dev, vector)) {
>          msix_set_pending(dev, vector);
>          return;
> @@ -427,7 +413,7 @@ void msix_reset(PCIDevice *dev)
>      if (!msix_present(dev)) {
>          return;
>      }
> -    msix_free_irq_entries(dev);
> +    msix_clear_all_vectors(dev);
>      dev->config[dev->msix_cap + MSIX_CONTROL_OFFSET] &=
>           ~dev->wmask[dev->msix_cap + MSIX_CONTROL_OFFSET];
>      memset(dev->msix_table, 0, dev->msix_entries_nr * PCI_MSIX_ENTRY_SIZE);
> @@ -435,41 +421,24 @@ void msix_reset(PCIDevice *dev)
>      msix_mask_all(dev, dev->msix_entries_nr);
>  }
>  
> -/* PCI spec suggests that devices make it possible for software to configure
> - * less vectors than supported by the device, but does not specify a standard
> - * mechanism for devices to do so.
> - *
> - * We support this by asking devices to declare vectors software is going to
> - * actually use, and checking this on the notification path. Devices that
> - * don't want to follow the spec suggestion can declare all vectors as used. 
> */
> -
> -/* Mark vector as used. */
> -int msix_vector_use(PCIDevice *dev, unsigned vector)
> +/* Clear pending vector. */
> +void msix_clear_vector(PCIDevice *dev, unsigned vector)
>  {
> -    if (vector >= dev->msix_entries_nr)
> -        return -EINVAL;
> -    dev->msix_entry_used[vector]++;
> -    return 0;
> -}
> -
> -/* Mark vector as unused. */
> -void msix_vector_unuse(PCIDevice *dev, unsigned vector)
> -{
> -    if (vector >= dev->msix_entries_nr || !dev->msix_entry_used[vector]) {
> -        return;
> -    }
> -    if (--dev->msix_entry_used[vector]) {
> -        return;
> +    if (msix_present(dev) && vector < dev->msix_entries_nr) {
> +        msix_clr_pending(dev, vector);
>      }
> -    msix_clr_pending(dev, vector);
>  }
>  
> -void msix_unuse_all_vectors(PCIDevice *dev)
> +void msix_clear_all_vectors(PCIDevice *dev)
>  {
> +    unsigned int vector;
> +
>      if (!msix_present(dev)) {
>          return;
>      }
> -    msix_free_irq_entries(dev);
> +    for (vector = 0; vector < dev->msix_entries_nr; ++vector) {
> +        msix_clr_pending(dev, vector);
> +    }
>  }
>  
>  unsigned int msix_nr_vectors_allocated(const PCIDevice *dev)
> diff --git a/hw/msix.h b/hw/msix.h
> index 1786e27..f235e32 100644
> --- a/hw/msix.h
> +++ b/hw/msix.h
> @@ -25,9 +25,8 @@ void msix_load(PCIDevice *dev, QEMUFile *f);
>  int msix_enabled(PCIDevice *dev);
>  int msix_present(PCIDevice *dev);
>  
> -int msix_vector_use(PCIDevice *dev, unsigned vector);
> -void msix_vector_unuse(PCIDevice *dev, unsigned vector);
> -void msix_unuse_all_vectors(PCIDevice *dev);
> +void msix_clear_vector(PCIDevice *dev, unsigned vector);
> +void msix_clear_all_vectors(PCIDevice *dev);
>  
>  void msix_notify(PCIDevice *dev, unsigned vector);
>  
> diff --git a/hw/pci.h b/hw/pci.h
> index 6c80442..e4a2603 100644
> --- a/hw/pci.h
> +++ b/hw/pci.h
> @@ -238,8 +238,6 @@ struct PCIDevice {
>      /* Memory Regions for MSIX table and pending bit entries. */
>      MemoryRegion msix_table_mmio;
>      MemoryRegion msix_pba_mmio;
> -    /* Reference-count for entries actually in use by driver. */
> -    unsigned *msix_entry_used;
>      /* MSIX function mask set or MSIX disabled */
>      bool msix_function_masked;
>      /* Version id needed for VMState */
> diff --git a/hw/virtio-pci.c b/hw/virtio-pci.c
> index 6ed21b7..34a936e 100644
> --- a/hw/virtio-pci.c
> +++ b/hw/virtio-pci.c
> @@ -137,9 +137,6 @@ static int virtio_pci_load_config(void * opaque, QEMUFile 
> *f)
>      } else {
>          proxy->vdev->config_vector = VIRTIO_NO_VECTOR;
>      }
> -    if (proxy->vdev->config_vector != VIRTIO_NO_VECTOR) {
> -        return msix_vector_use(&proxy->pci_dev, proxy->vdev->config_vector);
> -    }
>      return 0;
>  }
>  
> @@ -153,9 +150,6 @@ static int virtio_pci_load_queue(void * opaque, int n, 
> QEMUFile *f)
>          vector = VIRTIO_NO_VECTOR;
>      }
>      virtio_queue_set_vector(proxy->vdev, n, vector);
> -    if (vector != VIRTIO_NO_VECTOR) {
> -        return msix_vector_use(&proxy->pci_dev, vector);
> -    }
>      return 0;
>  }
>  
> @@ -300,7 +294,7 @@ static void virtio_ioport_write(void *opaque, uint32_t 
> addr, uint32_t val)
>          if (pa == 0) {
>              virtio_pci_stop_ioeventfd(proxy);
>              virtio_reset(proxy->vdev);
> -            msix_unuse_all_vectors(&proxy->pci_dev);
> +            msix_clear_all_vectors(&proxy->pci_dev);
>          }
>          else
>              virtio_queue_set_addr(vdev, vdev->queue_sel, pa);
> @@ -327,7 +321,7 @@ static void virtio_ioport_write(void *opaque, uint32_t 
> addr, uint32_t val)
>  
>          if (vdev->status == 0) {
>              virtio_reset(proxy->vdev);
> -            msix_unuse_all_vectors(&proxy->pci_dev);
> +            msix_clear_all_vectors(&proxy->pci_dev);
>          }
>  
>          /* Linux before 2.6.34 sets the device as OK without enabling
> @@ -339,18 +333,20 @@ static void virtio_ioport_write(void *opaque, uint32_t 
> addr, uint32_t val)
>          }
>          break;
>      case VIRTIO_MSI_CONFIG_VECTOR:
> -        msix_vector_unuse(&proxy->pci_dev, vdev->config_vector);
> +        msix_clear_vector(&proxy->pci_dev, vdev->config_vector);
>          /* Make it possible for guest to discover an error took place. */
> -        if (msix_vector_use(&proxy->pci_dev, val) < 0)
> +        if (val >= vdev->nvectors) {
>              val = VIRTIO_NO_VECTOR;
> +        }
>          vdev->config_vector = val;
>          break;
>      case VIRTIO_MSI_QUEUE_VECTOR:
> -        msix_vector_unuse(&proxy->pci_dev,
> +        msix_clear_vector(&proxy->pci_dev,
>                            virtio_queue_vector(vdev, vdev->queue_sel));
>          /* Make it possible for guest to discover an error took place. */
> -        if (msix_vector_use(&proxy->pci_dev, val) < 0)
> +        if (val >= vdev->nvectors) {
>              val = VIRTIO_NO_VECTOR;
> +        }
>          virtio_queue_set_vector(vdev, vdev->queue_sel, val);
>          break;
>      default:
> -- 
> 1.7.3.4