On Wed, Feb 09, 2022 at 04:00:34PM +0800, Tony Lu wrote: > On Tue, Feb 08, 2022 at 11:32:23AM +0200, Leon Romanovsky wrote: > > On Tue, Feb 08, 2022 at 10:10:55AM +0100, Stefan Raspl wrote: > > > On 2/7/22 14:49, Leon Romanovsky wrote: > > > > On Mon, Feb 07, 2022 at 05:59:58PM +0800, Tony Lu wrote: > > > > > On Mon, Jan 31, 2022 at 09:20:52AM +0200, Leon Romanovsky wrote: > > > > > > On Mon, Jan 31, 2022 at 03:03:00AM +0800, Tony Lu wrote: > > > > > > > Currently, pages are allocated in the process context, for its NUMA node > > > > > > > isn't equal to ibdev's, which is not the best policy for performance. > > > > > > > > > > > > > > Applications will generally perform best when the processes are > > > > > > > accessing memory on the same NUMA node. When numa_balancing enabled > > > > > > > (which is enabled by most of OS distributions), it moves tasks closer to > > > > > > > the memory of sndbuf or rmb and ibdev, meanwhile, the IRQs of ibdev bind > > > > > > > to the same node usually. This reduces the latency when accessing remote > > > > > > > memory. > > > > > > > > > > > > It is very subjective per-specific test. I would expect that > > > > > > application will control NUMA memory policies (set_mempolicy(), ...) > > > > > > by itself without kernel setting NUMA node. > > > > > > > > > > > > Various *_alloc_node() APIs are applicable for in-kernel allocations > > > > > > where user can't control memory policy. > > > > > > > > > > > > I don't know SMC-R enough, but if I judge from your description, this > > > > > > allocation is controlled by the application. > > > > > > > > > > The original design of SMC doesn't handle the memory allocation of > > > > > different NUMA node, and the application can't control the NUMA policy > > > > > in SMC. > > > > > > > > > > It allocates memory according to the NUMA node based on the process > > > > > context, which is determined by the scheduler. If application process > > > > > runs on NUMA node 0, SMC allocates on node 0 and so on, it all depends > > > > > on the scheduler. If RDMA device is attached to node 1, the process runs > > > > > on node 0, it allocates memory on node 0. > > > > > > > > > > This patch tries to allocate memory on the same NUMA node of RDMA > > > > > device. Applications can't know the current node of RDMA device. The > > > > > scheduler knows the node of memory, and can let applications run on the > > > > > same node of memory and RDMA device. > > > > > > > > I don't know, everything explained above is controlled through memory > > > > policy, where application needs to run on same node as ibdev. > > > > > > The purpose of SMC-R is to provide a drop-in replacement for existing TCP/IP > > > applications. The idea is to avoid almost any modification to the > > > application, just switch the address family. So while what you say makes a > > > lot of sense for applications that intend to use RDMA, in the case of SMC-R > > > we can safely assume that most if not all applications running it assume > > > they get connectivity through a non-RDMA NIC. Hence we cannot expect the > > > applications to think about aspects such as NUMA, and we should do the right > > > thing within SMC-R. > > > > And here comes the problem, you are doing the right thing for very > > specific and narrow use case, where application and ibdev run on > > same node. It is not true for multi-core systems as application will > > be scheduled on less load node (in very simplistic form). > > > > In general case, the application will get CPU and memory based on scheduler > > heuristic as you don't use memory policy to restrict it. The assumption > > that allocations need to be close to ibdev and not to applications can > > lead to worse performance. > > > > Yes, the applications cannot run faster if they always access remote > memory. There are something complex in SMC, so choose to bind to the > RDMA device. > > As Stefan mentioned, SMC is to provide a drop-in replacement for TCP. If I'm looking on the right piece of code (net/core/skbuff.c:build_skb), even SKB is not allocated close to ehternet device. I'm not convinced that SMC should be different here. Thanks
