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David Alan Gilbert" , qemu-devel@nongnu.org, Eric Auger , Kirti Wankhede , qemu-arm@nongnu.org, yuzenghui@huawei.com, wanghaibin.wang@huawei.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, 27 Jan 2021 19:27:35 +0800 Shenming Lu wrote: > On 2021/1/27 5:36, Alex Williamson wrote: > > On Wed, 9 Dec 2020 16:09:19 +0800 > > Shenming Lu wrote: > > > >> Different from the normal situation when the guest starts, we can > >> know the max unmasked vetctor (at the beginning) after msix_load() > >> in VFIO migration. So in order to avoid ineffectively disabling and > > > > s/ineffectively/inefficiently/? It's "effective" either way I think. > > Yeah, I should say "inefficiently". :-) > > > > >> enabling vectors repeatedly, let's allocate all needed vectors first > >> and then enable these unmasked vectors one by one without disabling. > >> > >> Signed-off-by: Shenming Lu > >> --- > >> hw/pci/msix.c | 17 +++++++++++++++++ > >> hw/vfio/pci.c | 10 ++++++++-- > >> include/hw/pci/msix.h | 2 ++ > >> 3 files changed, 27 insertions(+), 2 deletions(-) > >> > >> diff --git a/hw/pci/msix.c b/hw/pci/msix.c > >> index 67e34f34d6..bf291d3ff8 100644 > >> --- a/hw/pci/msix.c > >> +++ b/hw/pci/msix.c > >> @@ -557,6 +557,23 @@ unsigned int msix_nr_vectors_allocated(const PCIDevice *dev) > >> return dev->msix_entries_nr; > >> } > >> > >> +int msix_get_max_unmasked_vector(PCIDevice *dev) > >> +{ > >> + int max_unmasked_vector = -1; > >> + int vector; > >> + > >> + if ((dev->config[dev->msix_cap + MSIX_CONTROL_OFFSET] & > >> + (MSIX_ENABLE_MASK | MSIX_MASKALL_MASK)) == MSIX_ENABLE_MASK) { > >> + for (vector = 0; vector < dev->msix_entries_nr; vector++) { > >> + if (!msix_is_masked(dev, vector)) { > >> + max_unmasked_vector = vector; > >> + } > >> + } > >> + } > >> + > >> + return max_unmasked_vector; > >> +} > > > > Comments from QEMU PCI folks? > > > >> + > >> static int msix_set_notifier_for_vector(PCIDevice *dev, unsigned int vector) > >> { > >> MSIMessage msg; > >> diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c > >> index 51dc373695..e755ed2514 100644 > >> --- a/hw/vfio/pci.c > >> +++ b/hw/vfio/pci.c > >> @@ -568,6 +568,9 @@ static void vfio_msix_vector_release(PCIDevice *pdev, unsigned int nr) > >> > >> static void vfio_msix_enable(VFIOPCIDevice *vdev) > >> { > >> + int max_unmasked_vector = msix_get_max_unmasked_vector(&vdev->pdev); > >> + unsigned int used_vector = MAX(max_unmasked_vector, 0); > >> + > > > > The above PCI function could also be done inline here pretty easily too: > > > > unsigned int nr, max_vec = 0; > > > > if (!msix_masked(&vdev->pdev)) > > for (nr = 0; nr < msix_nr_vectors_allocated(&vdev->pdev); nr++) { > > if (!msix_is_masked(&vdev->pdev, nr)) { > > max_vec = nr; > > } > > } > > } > > > > It's a bit cleaner than the msix utility function, imo. > > Yeah, it makes sense. > > > > >> vfio_disable_interrupts(vdev); > >> > >> vdev->msi_vectors = g_new0(VFIOMSIVector, vdev->msix->entries); > >> @@ -586,9 +589,12 @@ static void vfio_msix_enable(VFIOPCIDevice *vdev) > >> * triggering to userspace, then immediately release the vector, leaving > >> * the physical device with no vectors enabled, but MSI-X enabled, just > >> * like the guest view. > >> + * If there are unmasked vectors (such as in migration) which will be > >> + * enabled soon, we can allocate them here to avoid ineffectively disabling > >> + * and enabling vectors repeatedly later. > > > > It just happens that migration triggers this usage model where the > > MSI-X enable bit is set with vectors unmasked in the vector table, but > > this is not unique to migration, guests can follow this pattern as well. > > Has this been tested with a variety of guests? Logically it seems > > correct, but always good to prove so. Thanks, > > I have tested it in migration and normal guest startup (only the latest Linux). > And I can try to test with some other kernels, could you be more specific about this? Minimally also Windows, ideally a BSD as well. Thanks, Alex > >> */ > >> - vfio_msix_vector_do_use(&vdev->pdev, 0, NULL, NULL); > >> - vfio_msix_vector_release(&vdev->pdev, 0); > >> + vfio_msix_vector_do_use(&vdev->pdev, used_vector, NULL, NULL); > >> + vfio_msix_vector_release(&vdev->pdev, used_vector); > >> > >> if (msix_set_vector_notifiers(&vdev->pdev, vfio_msix_vector_use, > >> vfio_msix_vector_release, NULL)) { > >> diff --git a/include/hw/pci/msix.h b/include/hw/pci/msix.h > >> index 4c4a60c739..4bfb463fa6 100644 > >> --- a/include/hw/pci/msix.h > >> +++ b/include/hw/pci/msix.h > >> @@ -23,6 +23,8 @@ void msix_uninit_exclusive_bar(PCIDevice *dev); > >> > >> unsigned int msix_nr_vectors_allocated(const PCIDevice *dev); > >> > >> +int msix_get_max_unmasked_vector(PCIDevice *dev); > >> + > >> void msix_save(PCIDevice *dev, QEMUFile *f); > >> void msix_load(PCIDevice *dev, QEMUFile *f); > >> > > > > . > > >