Brice aha. thanks. I knew I'd seen a function for that, but couldn't remember what it was.
Cheers JB ________________________________________ From: hwloc-users [hwloc-users-boun...@lists.open-mpi.org] on behalf of Brice Goglin [brice.gog...@inria.fr] Sent: 13 November 2017 14:57 To: Hardware locality user list Subject: Re: [hwloc-users] question about hwloc_set_area_membind_nodeset Use get_area_memlocation() membind() returns where the pages are *allowed* to go (anywhere) memlocation() returns where the pages are actually allocated. Brice Le 13/11/2017 06:52, Biddiscombe, John A. a écrit : > Thank you to you both. > > I modified the allocator to allocate one large block using hwloc_alloc and > then use one thread per numa domain to touch each page according to the > tiling pattern - unfortunately, I hadn't appreciated that now > hwloc_get_area_membind_nodeset > always returns the full machine numa mask - and not the numa domain that the > page was touched by (I guess it only gives the expected answer when > set_area_membind is used first) > > I had hoped to use a dynamic query of the pages (using the first one of a > given tile) to schedule each task that operates on a given tile to run on the > numa node that touched it. > > I can work around this by using a matrix offset calculation to get the numa > node, but if there's a way of querying the page directly - then please let me > know. > > Thanks > > JB > ________________________________________ > From: hwloc-users [hwloc-users-boun...@lists.open-mpi.org] on behalf of > Samuel Thibault [samuel.thiba...@inria.fr] > Sent: 12 November 2017 10:48 > To: Hardware locality user list > Subject: Re: [hwloc-users] question about hwloc_set_area_membind_nodeset > > Brice Goglin, on dim. 12 nov. 2017 05:19:37 +0100, wrote: >> That's likely what's happening. Each set_area() may be creating a new >> "virtual >> memory area". The kernel tries to merge them with neighbors if they go to the >> same NUMA node. Otherwise it creates a new VMA. > Mmmm, that sucks. Ideally we'd have a way to ask the kernel not to > strictly bind the memory, but just to allocate on a given memory > node, and just hope that the allocation will not go away (e.g. due to > swapping), which thus doesn't need a VMA to record the information. As > you describe below, first-touch achieves that but it's not necessarily > so convenient. > >> I can't find the exact limit but it's something like 64k so I guess >> you're exhausting that. > It's sysctl vm.max_map_count > >> Question 2 : Is there a better way of achieving the result I'm looking >> for >> (such as a call to membind with a stride of some kind to say put N pages >> in >> a row on each domain in alternation). >> >> >> Unfortunately, the interleave policy doesn't have a stride argument. It's one >> page on node 0, one page on node 1, etc. >> >> The only idea I have is to use the first-touch policy: Make sure your buffer >> isn't is physical memory yet, and have a thread on node 0 read the "0" pages, >> and another thread on node 1 read the "1" page. > Or "next-touch" if that was to ever get merged into mainline Linux :) > > Samuel > _______________________________________________ > hwloc-users mailing list > hwloc-users@lists.open-mpi.org > https://lists.open-mpi.org/mailman/listinfo/hwloc-users > _______________________________________________ > hwloc-users mailing list > hwloc-users@lists.open-mpi.org > https://lists.open-mpi.org/mailman/listinfo/hwloc-users _______________________________________________ hwloc-users mailing list hwloc-users@lists.open-mpi.org https://lists.open-mpi.org/mailman/listinfo/hwloc-users _______________________________________________ hwloc-users mailing list hwloc-users@lists.open-mpi.org https://lists.open-mpi.org/mailman/listinfo/hwloc-users
