On Thu, Jul 25, 2019 at 10:00:25AM -0600, Logan Gunthorpe wrote: > > > On 2019-07-25 12:10 a.m., Christoph Hellwig wrote: > > On Wed, Jul 24, 2019 at 09:58:59AM -0600, Logan Gunthorpe wrote: > >> > >> > >> On 2019-07-24 12:32 a.m., Christoph Hellwig wrote: > >>>> struct dev_pagemap *pgmap = sg_page(sg)->pgmap; > >>>> + struct pci_dev *client; > >>>> + int dist; > >>>> + > >>>> + client = find_parent_pci_dev(dev); > >>>> + if (WARN_ON_ONCE(!client)) > >>>> + return 0; > >>>> > >>>> + dist = upstream_bridge_distance(pgmap->pci_p2pdma_provider, > >>>> + client, NULL); > >>> > >>> Doing this on every mapping call sounds expensive.. > >> > >> The result of this function is cached in an xarray (per patch 4) so, on > >> the hot path, it should just be a single xa_load() which should be a > >> relatively fast lookup which is similarly used for other hot path > >> operations. > > > > We don't cache find_parent_pci_dev, though. So we should probably > > export find_parent_pci_dev with a proper namespaces name and cache > > that in the caler. > > Oh, yes, I'll take a look at this. Of the two callers: NVMe should be > easy we could just pass the PCI device instead of the struct device. > RDMA is significantly more unclear: would you add a pci_dev to struct > ib_device? Or maybe we should be able to simply rely on the fact that > the DMA device *must* be a PCI device and just use to_pci_dev() directly? AFAIK you need to use the ib_device->dma_device and add some kind of is_pci_dev to make it safe Jason
