On 11/18/20 11:38 AM, Jason Gunthorpe wrote: > On Wed, Nov 18, 2020 at 11:03:24AM -0700, David Ahern wrote: > >> With Connectx-4 Lx for example the netdev can have at most 63 queues > > What netdev calls a queue is really a "can the device deliver > interrupts and packets to a given per-CPU queue" and covers a whole > spectrum of smaller limits like RSS scheme, # of available interrupts, > ability of the device to create queues, etc. > > CX4Lx can create a huge number of queues, but hits one of these limits > that mean netdev's specific usage can't scale up. Other stuff like > RDMA doesn't have the same limits, and has tonnes of queues. > > What seems to be needed is a resource controller concept like cgroup > has for processes. The system is really organized into a tree: > > physical device > mlx5_core > / | \ \ (aux bus) > netdev rdma vdpa SF etc > | (aux bus) > mlx5_core > / \ (aux bus) > netdev vdpa > > And it does make a lot of sense to start to talk about limits at each > tree level. > > eg the top of the tree may have 128 physical interrupts. With 128 CPU > cores that isn't enough interrupts to support all of those things > concurrently. > > So the user may want to configure: > - The first level netdev only gets 64, > - 3rd level mlx5_core gets 32 > - Final level vdpa gets 8 > > Other stuff has to fight it out with the remaining shared interrupts. > > In netdev land # of interrupts governs # of queues > > For RDMA # of interrupts limits the CPU affinities for queues > > VPDA limits the # of VMs that can use VT-d > > The same story repeats for other less general resources, mlx5 also > has consumption of limited BAR space, and consumption of some limited > memory elements. These numbers are much bigger and may not need > explicit governing, but the general concept holds. > > It would be very nice if the limit could be injected when the aux > device is created but before the driver is bound. I'm not sure how to > manage that though.. > > I assume other devices will be different, maybe some devices have a > limit on the number of total queues, or a limit on the number of > VDPA or RDMA devices. > > Jason > A lot of low level resource details that need to be summarized into a nicer user / config perspective to specify limits / allocations. Thanks for the detailed response.
