On Wed, Feb 13, 2019 at 10:41:55PM +0100, Thomas Gleixner wrote: > Btw, while I have your attention. There popped up an issue recently related > to that affinity logic. > > The current implementation fails when: > > /* > * If there aren't any vectors left after applying the pre/post > * vectors don't bother with assigning affinity. > */ > if (nvecs == affd->pre_vectors + affd->post_vectors) > return NULL; > > Now the discussion arised, that in that case the affinity sets are not > allocated and filled in for the pre/post vectors, but somehow the > underlying device still works and later on triggers the warning in the > blk-mq code because the MSI entries do not have affinity information > attached. > > Sure, we could make that work, but there are several issues: > > 1) irq_create_affinity_masks() has another reason to return NULL: > memory allocation fails. > > 2) Does it make sense at all. > > Right now the PCI allocator ignores the NULL return and proceeds without > setting any affinities. As a consequence nothing is managed and everything > happens to work. > > But that happens to work is more by chance than by design and the warning > is bogus if this is an expected mode of operation. > > We should address these points in some way. Ah, yes, that's a mistake in the nvme driver. It is assuming IO queues are always on managed interrupts, but that's not true if when only 1 vector could be allocated. This should be an appropriate fix to the warning: --- diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c index 022ea1ee63f8..f2ccebe1c926 100644 --- a/drivers/nvme/host/pci.c +++ b/drivers/nvme/host/pci.c @@ -506,7 +506,7 @@ static int nvme_pci_map_queues(struct blk_mq_tag_set *set) * affinity), so use the regular blk-mq cpu mapping */ map->queue_offset = qoff; - if (i != HCTX_TYPE_POLL) + if (i != HCTX_TYPE_POLL && dev->num_vecs > 1) blk_mq_pci_map_queues(map, to_pci_dev(dev->dev), offset); else blk_mq_map_queues(map); --
