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

[Jan Kiszka <jan.kiszka@web.de>]

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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



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