RE: [PATCH 3/4 net-next] net: mana: add a function to spread IRQs per CPUs
From: Michael Kelley <hidden>
Date: 2024-01-09 19:22:43
Also in:
linux-hyperv, linux-rdma, lkml
From: Souradeep Chakrabarti <redacted> Sent: Tuesday, January 9, 2024 2:51 AM
From: Yury Norov <yury.norov@gmail.com> Souradeep investigated that the driver performs faster if IRQs are spread on CPUs with the following heuristics: 1. No more than one IRQ per CPU, if possible; 2. NUMA locality is the second priority; 3. Sibling dislocality is the last priority. Let's consider this topology: Node 0 1 Core 0 1 2 3 CPU 0 1 2 3 4 5 6 7 The most performant IRQ distribution based on the above topology and heuristics may look like this: IRQ Nodes Cores CPUs 0 1 0 0-1 1 1 1 2-3 2 1 0 0-1 3 1 1 2-3 4 2 2 4-5 5 2 3 6-7 6 2 2 4-5 7 2 3 6-7
I didn't pay attention to the detailed discussion of this issue over the past 2 to 3 weeks during the holidays in the U.S., but the above doesn't align with the original problem as I understood it. I thought the original problem was to avoid putting IRQs on both hyper-threads in the same core, and that the perf improvements are based on that configuration. At least that's what the commit message for Patch 4/4 in this series says. The above chart results in 8 IRQs being assigned to the 8 CPUs, probably with 1 IRQ per CPU. At least on x86, if the affinity mask for an IRQ contains multiple CPUs, matrix_find_best_cpu() should balance the IRQ assignments between the CPUs in the mask. So the original problem is still present because both hyper-threads in a core are likely to have an IRQ assigned. Of course, this example has 8 IRQs and 8 CPUs, so assigning an IRQ to every hyper-thread may be the only choice. If that's the case, maybe this just isn't a good example to illustrate the original problem and solution. But even with a better example where the # of IRQs is <= half the # of CPUs in a NUMA node, I don't think the code below accomplishes the original intent. Maybe I've missed something along the way in getting to this version of the patch. Please feel free to set me straight. :-) Michael
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The irq_setup() routine introduced in this patch leverages the for_each_numa_hop_mask() iterator and assigns IRQs to sibling groups as described above. According to [1], for NUMA-aware but sibling-ignorant IRQ distribution based on cpumask_local_spread() performance test results look like this: /ntttcp -r -m 16 NTTTCP for Linux 1.4.0 --------------------------------------------------------- 08:05:20 INFO: 17 threads created 08:05:28 INFO: Network activity progressing... 08:06:28 INFO: Test run completed. 08:06:28 INFO: Test cycle finished. 08:06:28 INFO: ##### Totals: ##### 08:06:28 INFO: test duration :60.00 seconds 08:06:28 INFO: total bytes :630292053310 08:06:28 INFO: throughput :84.04Gbps 08:06:28 INFO: retrans segs :4 08:06:28 INFO: cpu cores :192 08:06:28 INFO: cpu speed :3799.725MHz 08:06:28 INFO: user :0.05% 08:06:28 INFO: system :1.60% 08:06:28 INFO: idle :96.41% 08:06:28 INFO: iowait :0.00% 08:06:28 INFO: softirq :1.94% 08:06:28 INFO: cycles/byte :2.50 08:06:28 INFO: cpu busy (all) :534.41% For NUMA- and sibling-aware IRQ distribution, the same test works 15% faster: /ntttcp -r -m 16 NTTTCP for Linux 1.4.0 --------------------------------------------------------- 08:08:51 INFO: 17 threads created 08:08:56 INFO: Network activity progressing... 08:09:56 INFO: Test run completed. 08:09:56 INFO: Test cycle finished. 08:09:56 INFO: ##### Totals: ##### 08:09:56 INFO: test duration :60.00 seconds 08:09:56 INFO: total bytes :741966608384 08:09:56 INFO: throughput :98.93Gbps 08:09:56 INFO: retrans segs :6 08:09:56 INFO: cpu cores :192 08:09:56 INFO: cpu speed :3799.791MHz 08:09:56 INFO: user :0.06% 08:09:56 INFO: system :1.81% 08:09:56 INFO: idle :96.18% 08:09:56 INFO: iowait :0.00% 08:09:56 INFO: softirq :1.95% 08:09:56 INFO: cycles/byte :2.25 08:09:56 INFO: cpu busy (all) :569.22% [1] https://lore.kernel.org/all/20231211063726.GA4977@linuxonhyperv3.guj3 yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net/ Signed-off-by: Yury Norov <yury.norov@gmail.com> Co-developed-by: Souradeep Chakrabarti [off-list ref] --- .../net/ethernet/microsoft/mana/gdma_main.c | 29 +++++++++++++++++++ 1 file changed, 29 insertions(+)diff --git a/drivers/net/ethernet/microsoft/mana/gdma_main.cb/drivers/net/ethernet/microsoft/mana/gdma_main.c index 6367de0c2c2e..6a967d6be01e 100644--- a/drivers/net/ethernet/microsoft/mana/gdma_main.c +++ b/drivers/net/ethernet/microsoft/mana/gdma_main.c@@ -1243,6 +1243,35 @@ void mana_gd_free_res_map(struct gdma_resource *r) r->size = 0; } +static __maybe_unused int irq_setup(unsigned int *irqs, unsigned int len, int node) +{ + const struct cpumask *next, *prev = cpu_none_mask; + cpumask_var_t cpus __free(free_cpumask_var); + int cpu, weight; + + if (!alloc_cpumask_var(&cpus, GFP_KERNEL)) + return -ENOMEM; + + rcu_read_lock(); + for_each_numa_hop_mask(next, node) { + weight = cpumask_weight_andnot(next, prev); + while (weight > 0) { + cpumask_andnot(cpus, next, prev); + for_each_cpu(cpu, cpus) { + if (len-- == 0) + goto done; + irq_set_affinity_and_hint(*irqs++, topology_sibling_cpumask(cpu)); + cpumask_andnot(cpus, cpus, topology_sibling_cpumask(cpu)); + --weight; + } + } + prev = next; + } +done: + rcu_read_unlock(); + return 0; +} + static int mana_gd_setup_irqs(struct pci_dev *pdev) { unsigned int max_queues_per_port = num_online_cpus(); --2.34.1