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

["Michael S. Tsirkin" <mst@redhat.com>]

On Fri, Aug 24, 2012 at 10:21:44AM +0200, 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 <jan.kiszka@siemens.com>
> >>
> >> 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 <jan.kiszka@siemens.com>
> >> ---
> >>
> >> 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.
> 
> Jan
> 
> 

I'd like to keep it for virtio and remove for everyone else.
Draft patch sent, it's weekend here so consider it
pseudo-code, pls take a look.

-- 
MST