On Tue, Sep 06, 2016 at 06:50:56PM +0200, Christoph Hellwig wrote: > [adding Thomas as it's about the affinity_mask he (we) added to the > IRQ core] > > Here's my topology info: > > > > # numactl --hardware > > available: 2 nodes (0-1) > > node 0 cpus: 0 1 2 3 4 5 6 7 16 17 18 19 20 21 22 23 > > node 0 size: 15745 MB > > node 0 free: 15319 MB > > node 1 cpus: 8 9 10 11 12 13 14 15 24 25 26 27 28 29 30 31 > > node 1 size: 16150 MB > > node 1 free: 15758 MB > > node distances: > > node 0 1 > > 0: 10 21 > > 1: 21 10 > > How do you get that mapping? Does this CPU use Hyperthreading and > thus expose siblings using topology_sibling_cpumask? As that's the > only thing the old code used for any sort of special casing. > > I'll need to see if I can find a system with such a mapping to reproduce. Yes, this is a two-socket server with hyperthreading enabled. Numbering the physical CPUs before the hyperthreads is a common numbering on x86, so we're going to see this split numbering on any multi-socket hyperthreaded server. The topology_sibling_cpumask shows the right information. The resulting mask from cpu 0 on my server is 0x00010001; cpu 1 is 0x00020002, etc... > > What we want for my CPU topology is the 16th CPU to pair with CPU 0, > > 17 pairs with 1, 18 with 2, and so on. You can't convey that information > > with this scheme. We need affinity_masks per vector. > > We actually have per-vector masks, but they are hidden inside the IRQ > core and awkward to use. We could to the get_first_sibling magic > in the block-mq queue mapping (and in fact with the current code I guess > we need to). Or take a step back from trying to emulate the old code > and instead look at NUMA nodes instead of siblings which some folks > suggested a while ago. Adding the first sibling magic in blk-mq would fix my specific case, but it doesn't help genericly when we need to pair more than just thread siblings. -- To unsubscribe from this list: send the line "unsubscribe linux-block" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
