![Ming Lei](/assets/img/avatar_default.png)
Commit84676c1f21
("genirq/affinity: assign vectors to all possible CPUs") tried to spread the interrupts accross all possible CPUs to make sure that in case of phsyical hotplug (e.g. virtualization) the CPUs which get plugged in after the device was initialized are targeted by a hardware queue and the corresponding interrupt. This has a downside in cases where the ACPI tables claim that there are more possible CPUs than present CPUs and the number of interrupts to spread out is smaller than the number of possible CPUs. These bogus ACPI tables are unfortunately not uncommon. In such a case the vector spreading algorithm assigns interrupts to CPUs which can never be utilized and as a consequence these interrupts are unused instead of being mapped to present CPUs. As a result the performance of the device is suboptimal. To fix this spread the interrupt vectors in two stages: 1) Spread as many interrupts as possible among the present CPUs 2) Spread the remaining vectors among non present CPUs On a 8 core system, where CPU 0-3 are present and CPU 4-7 are not present, for a device with 4 queues the resulting interrupt affinity is: 1) Before84676c1f21
("genirq/affinity: assign vectors to all possible CPUs") irq 39, cpu list 0 irq 40, cpu list 1 irq 41, cpu list 2 irq 42, cpu list 3 2) With84676c1f21
("genirq/affinity: assign vectors to all possible CPUs") irq 39, cpu list 0-2 irq 40, cpu list 3-4,6 irq 41, cpu list 5 irq 42, cpu list 7 3) With the refined vector spread applied: irq 39, cpu list 0,4 irq 40, cpu list 1,6 irq 41, cpu list 2,5 irq 42, cpu list 3,7 On a 8 core system, where all CPUs are present the resulting interrupt affinity for the 4 queues is: irq 39, cpu list 0,1 irq 40, cpu list 2,3 irq 41, cpu list 4,5 irq 42, cpu list 6,7 This is independent of the number of CPUs which are online at the point of initialization because in such a system the offline CPUs can be easily onlined afterwards, while in non-present CPUs need to be plugged physically or virtually which requires external interaction. The downside of this approach is that in case of physical hotplug the interrupt vector spreading might be suboptimal when CPUs 4-7 are physically plugged. Suboptimal from a NUMA point of view and due to the single target nature of interrupt affinities the later plugged CPUs might not be targeted by interrupts at all. Though, physical hotplug systems are not the common case while the broken ACPI table disease is wide spread. So it's preferred to have as many interrupts as possible utilized at the point where the device is initialized. Block multi-queue devices like NVME create a hardware queue per possible CPU, so the goal of commit84676c1f21
to assign one interrupt vector per possible CPU is still achieved even with physical/virtual hotplug. [ tglx: Changed from online to present CPUs for the first spreading stage, renamed variables for readability sake, added comments and massaged changelog ] Reported-by: Laurence Oberman <loberman@redhat.com> Signed-off-by: Ming Lei <ming.lei@redhat.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: Christoph Hellwig <hch@lst.de> Cc: Jens Axboe <axboe@kernel.dk> Cc: linux-block@vger.kernel.org Cc: Christoph Hellwig <hch@infradead.org> Link: https://lkml.kernel.org/r/20180308105358.1506-5-ming.lei@redhat.com
271 lines
6.7 KiB
C
271 lines
6.7 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* Copyright (C) 2016 Thomas Gleixner.
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* Copyright (C) 2016-2017 Christoph Hellwig.
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*/
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#include <linux/interrupt.h>
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#include <linux/kernel.h>
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#include <linux/slab.h>
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#include <linux/cpu.h>
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static void irq_spread_init_one(struct cpumask *irqmsk, struct cpumask *nmsk,
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int cpus_per_vec)
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{
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const struct cpumask *siblmsk;
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int cpu, sibl;
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for ( ; cpus_per_vec > 0; ) {
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cpu = cpumask_first(nmsk);
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/* Should not happen, but I'm too lazy to think about it */
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if (cpu >= nr_cpu_ids)
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return;
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cpumask_clear_cpu(cpu, nmsk);
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cpumask_set_cpu(cpu, irqmsk);
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cpus_per_vec--;
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/* If the cpu has siblings, use them first */
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siblmsk = topology_sibling_cpumask(cpu);
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for (sibl = -1; cpus_per_vec > 0; ) {
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sibl = cpumask_next(sibl, siblmsk);
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if (sibl >= nr_cpu_ids)
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break;
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if (!cpumask_test_and_clear_cpu(sibl, nmsk))
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continue;
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cpumask_set_cpu(sibl, irqmsk);
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cpus_per_vec--;
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}
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}
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}
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static cpumask_var_t *alloc_node_to_cpumask(void)
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{
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cpumask_var_t *masks;
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int node;
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masks = kcalloc(nr_node_ids, sizeof(cpumask_var_t), GFP_KERNEL);
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if (!masks)
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return NULL;
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for (node = 0; node < nr_node_ids; node++) {
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if (!zalloc_cpumask_var(&masks[node], GFP_KERNEL))
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goto out_unwind;
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}
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return masks;
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out_unwind:
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while (--node >= 0)
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free_cpumask_var(masks[node]);
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kfree(masks);
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return NULL;
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}
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static void free_node_to_cpumask(cpumask_var_t *masks)
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{
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int node;
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for (node = 0; node < nr_node_ids; node++)
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free_cpumask_var(masks[node]);
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kfree(masks);
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}
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static void build_node_to_cpumask(cpumask_var_t *masks)
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{
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int cpu;
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for_each_possible_cpu(cpu)
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cpumask_set_cpu(cpu, masks[cpu_to_node(cpu)]);
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}
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static int get_nodes_in_cpumask(cpumask_var_t *node_to_cpumask,
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const struct cpumask *mask, nodemask_t *nodemsk)
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{
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int n, nodes = 0;
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/* Calculate the number of nodes in the supplied affinity mask */
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for_each_node(n) {
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if (cpumask_intersects(mask, node_to_cpumask[n])) {
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node_set(n, *nodemsk);
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nodes++;
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}
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}
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return nodes;
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}
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static int irq_build_affinity_masks(const struct irq_affinity *affd,
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int startvec, int numvecs,
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cpumask_var_t *node_to_cpumask,
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const struct cpumask *cpu_mask,
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struct cpumask *nmsk,
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struct cpumask *masks)
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{
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int n, nodes, cpus_per_vec, extra_vecs, done = 0;
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int last_affv = affd->pre_vectors + numvecs;
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int curvec = startvec;
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nodemask_t nodemsk = NODE_MASK_NONE;
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if (!cpumask_weight(cpu_mask))
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return 0;
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nodes = get_nodes_in_cpumask(node_to_cpumask, cpu_mask, &nodemsk);
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/*
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* If the number of nodes in the mask is greater than or equal the
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* number of vectors we just spread the vectors across the nodes.
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*/
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if (numvecs <= nodes) {
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for_each_node_mask(n, nodemsk) {
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cpumask_copy(masks + curvec, node_to_cpumask[n]);
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if (++done == numvecs)
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break;
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if (++curvec == last_affv)
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curvec = affd->pre_vectors;
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}
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goto out;
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}
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for_each_node_mask(n, nodemsk) {
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int ncpus, v, vecs_to_assign, vecs_per_node;
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/* Spread the vectors per node */
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vecs_per_node = (numvecs - (curvec - affd->pre_vectors)) / nodes;
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/* Get the cpus on this node which are in the mask */
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cpumask_and(nmsk, cpu_mask, node_to_cpumask[n]);
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/* Calculate the number of cpus per vector */
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ncpus = cpumask_weight(nmsk);
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vecs_to_assign = min(vecs_per_node, ncpus);
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/* Account for rounding errors */
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extra_vecs = ncpus - vecs_to_assign * (ncpus / vecs_to_assign);
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for (v = 0; curvec < last_affv && v < vecs_to_assign;
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curvec++, v++) {
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cpus_per_vec = ncpus / vecs_to_assign;
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/* Account for extra vectors to compensate rounding errors */
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if (extra_vecs) {
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cpus_per_vec++;
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--extra_vecs;
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}
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irq_spread_init_one(masks + curvec, nmsk, cpus_per_vec);
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}
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done += v;
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if (done >= numvecs)
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break;
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if (curvec >= last_affv)
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curvec = affd->pre_vectors;
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--nodes;
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}
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out:
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return done;
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}
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/**
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* irq_create_affinity_masks - Create affinity masks for multiqueue spreading
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* @nvecs: The total number of vectors
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* @affd: Description of the affinity requirements
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*
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* Returns the masks pointer or NULL if allocation failed.
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*/
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struct cpumask *
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irq_create_affinity_masks(int nvecs, const struct irq_affinity *affd)
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{
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int affvecs = nvecs - affd->pre_vectors - affd->post_vectors;
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int curvec, usedvecs;
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cpumask_var_t nmsk, npresmsk, *node_to_cpumask;
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struct cpumask *masks = NULL;
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/*
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* If there aren't any vectors left after applying the pre/post
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* vectors don't bother with assigning affinity.
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*/
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if (nvecs == affd->pre_vectors + affd->post_vectors)
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return NULL;
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if (!zalloc_cpumask_var(&nmsk, GFP_KERNEL))
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return NULL;
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if (!zalloc_cpumask_var(&npresmsk, GFP_KERNEL))
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goto outcpumsk;
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node_to_cpumask = alloc_node_to_cpumask();
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if (!node_to_cpumask)
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goto outnpresmsk;
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masks = kcalloc(nvecs, sizeof(*masks), GFP_KERNEL);
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if (!masks)
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goto outnodemsk;
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/* Fill out vectors at the beginning that don't need affinity */
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for (curvec = 0; curvec < affd->pre_vectors; curvec++)
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cpumask_copy(masks + curvec, irq_default_affinity);
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/* Stabilize the cpumasks */
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get_online_cpus();
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build_node_to_cpumask(node_to_cpumask);
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/* Spread on present CPUs starting from affd->pre_vectors */
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usedvecs = irq_build_affinity_masks(affd, curvec, affvecs,
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node_to_cpumask, cpu_present_mask,
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nmsk, masks);
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/*
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* Spread on non present CPUs starting from the next vector to be
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* handled. If the spreading of present CPUs already exhausted the
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* vector space, assign the non present CPUs to the already spread
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* out vectors.
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*/
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if (usedvecs >= affvecs)
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curvec = affd->pre_vectors;
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else
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curvec = affd->pre_vectors + usedvecs;
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cpumask_andnot(npresmsk, cpu_possible_mask, cpu_present_mask);
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usedvecs += irq_build_affinity_masks(affd, curvec, affvecs,
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node_to_cpumask, npresmsk,
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nmsk, masks);
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put_online_cpus();
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/* Fill out vectors at the end that don't need affinity */
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if (usedvecs >= affvecs)
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curvec = affd->pre_vectors + affvecs;
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else
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curvec = affd->pre_vectors + usedvecs;
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for (; curvec < nvecs; curvec++)
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cpumask_copy(masks + curvec, irq_default_affinity);
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outnodemsk:
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free_node_to_cpumask(node_to_cpumask);
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outnpresmsk:
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free_cpumask_var(npresmsk);
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outcpumsk:
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free_cpumask_var(nmsk);
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return masks;
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}
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/**
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* irq_calc_affinity_vectors - Calculate the optimal number of vectors
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* @minvec: The minimum number of vectors available
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* @maxvec: The maximum number of vectors available
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* @affd: Description of the affinity requirements
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*/
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int irq_calc_affinity_vectors(int minvec, int maxvec, const struct irq_affinity *affd)
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{
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int resv = affd->pre_vectors + affd->post_vectors;
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int vecs = maxvec - resv;
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int ret;
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if (resv > minvec)
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return 0;
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get_online_cpus();
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ret = min_t(int, cpumask_weight(cpu_possible_mask), vecs) + resv;
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put_online_cpus();
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return ret;
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}
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