Re: [Qemu-devel] [PATCH v2][for 1.2?] msix: Drop tracking of used vectors

[Michael S. Tsirkin]

On Fri, Aug 24, 2012 at 10:35:34AM +0200, Jan Kiszka wrote:
> On 2012-08-24 10:21, Jan Kiszka wrote:
> > On 2012-08-24 10:20, Michael S. Tsirkin wrote:
> >> On Fri, Aug 24, 2012 at 08:19:50AM +0200, Jan Kiszka wrote:
> >>> From: Jan Kiszka <address@hidden>
> >>>
> >>> This optimization was once used in qemu-kvm to keep KVM route usage low.
> >>> But now we solved that problem via lazy updates. It also tried to handle
> >>> the case of vectors shared between different sources of the same device.
> >>> However, this never really worked and will have to be addressed
> >>> differently anyway. 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.
> >>>
> >>> This also unbreaks MSI-X after reset for ivshmem and megasas as device
> >>> models can't easily mark their vectors used afterward (megasas didn't
> >>> even try).
> >>>
> >>> Signed-off-by: Jan Kiszka <address@hidden>
> >>> ---
> >>>
> >>> This patch has been posted some moons again, and we had a discussion
> >>> about the impact on the existing users. At that time, MSI-X refactoring
> >>> for KVM support was not yet merged. Now it is, and it should be better
> >>> much clearer that vector usage tracking has no business with that
> >>> feature.
> >>>
> >>>  hw/ivshmem.c    |   20 -------------------
> >>>  hw/megasas.c    |    4 ---
> >>>  hw/msix.c       |   57 
> >>> ++++++++++++------------------------------------------
> >>>  hw/msix.h       |    5 +--
> >>>  hw/pci.h        |    2 -
> >>>  hw/virtio-pci.c |   20 +++++++-----------
> >>>  6 files changed, 23 insertions(+), 85 deletions(-)
> >>>
> >>> diff --git a/hw/ivshmem.c b/hw/ivshmem.c
> >>> index 47f2a16..5ffff48 100644
> >>> --- a/hw/ivshmem.c
> >>> +++ b/hw/ivshmem.c
> >>> @@ -523,28 +523,11 @@ 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;
> >>>  }
> >>>  
> >>> @@ -586,8 +569,6 @@ 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)
> >>> @@ -629,7 +610,6 @@ 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/megasas.c b/hw/megasas.c
> >>> index c35a15d..4766117 100644
> >>> --- a/hw/megasas.c
> >>> +++ b/hw/megasas.c
> >>> @@ -2121,10 +2121,6 @@ static int megasas_scsi_init(PCIDevice *dev)
> >>>      pci_register_bar(&s->dev, 2, PCI_BASE_ADDRESS_SPACE_IO, &s->port_io);
> >>>      pci_register_bar(&s->dev, 3, bar_type, &s->queue_io);
> >>>  
> >>> -    if (megasas_use_msix(s)) {
> >>> -        msix_vector_use(&s->dev, 0);
> >>> -    }
> >>> -
> >>>      if (!s->sas_addr) {
> >>>          s->sas_addr = ((NAA_LOCALLY_ASSIGNED_ID << 24) |
> >>>                         IEEE_COMPANY_LOCALLY_ASSIGNED) << 36;
> >>> diff --git a/hw/msix.c b/hw/msix.c
> >>> index aea340b..163ce4c 100644
> >>> --- a/hw/msix.c
> >>> +++ b/hw/msix.c
> >>> @@ -273,7 +273,6 @@ 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);
> >>>  
> >>> @@ -326,16 +325,6 @@ 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)
> >>>  {
> >>> @@ -344,7 +333,6 @@ 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);
> >>> @@ -354,8 +342,6 @@ 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;
> >>>  }
> >>> @@ -390,7 +376,6 @@ 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);
> >>> @@ -419,8 +404,9 @@ 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;
> >>> @@ -436,7 +422,7 @@ 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);
> >>> @@ -444,41 +430,24 @@ 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;
> >>> -}
> >>> -
> >>
> >> I keep thinking we should instead call vector notifier
> >> here, so that virtio can detect and handle cases where
> >> kvm_virtio_pci_vq_vector_use fails.
> >> ATM it just asserts.
> >>
> >> Maybe I am wrong.
> >>
> >> Let's delay this decision until 1.3.
> > 
> > Yep, that feature can be added on top of this patch in 1.3, but we
> > should still remove the usage tracking to fix its issues. There is no
> > feature regression related to this.
> 
> OK, to address that virtio requirement (in 1.3) we can simply
> preallocate an MSI route on VIRTIO_MSI_CONFIG/QUEUE_VECTOR and update
> that route (I have a patch for kvm_irqchip_update_msi_route here
> already) on vector_use.
> 
> The point is: That all is pure virtio business, nothing the generic
> MSI-X layer nor any normal MSI-X device or even pci-assign/vfio have to
> deal with.
> 
> Jan
> 

Yes, I agree with that last statement.

-- 
MST