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SubjectRe: [PATCH v4] lib: optimize cpumask_local_spread()
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Hi Michal,

+Cc: Rusty Russell who optimised this function in commit
f36963c9d3f6 ("cpumask_set_cpu_local_first => cpumask_local_spread, lament")

On 2019/12/11 17:08, Michal Hocko wrote:
> On Wed 11-12-19 16:03:57, Shaokun Zhang wrote:
>> From: yuqi jin <jinyuqi@huawei.com>
>>
>> In multi-processor and NUMA system, I/O driver will find cpu cores that
>> which shall be bound IRQ. When cpu cores in the local numa have been
>> used, it is better to find the node closest to the local numa node for
>> performance, instead of choosing any online cpu immediately.
>>
>> On Huawei Kunpeng 920 server, there are 4 NUMA node(0 - 3) in the 2-cpu
>> system(0 - 1). The topology of this server is followed:
>> available: 4 nodes (0-3)
>> node 0 cpus: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
>> node 0 size: 63379 MB
>> node 0 free: 61899 MB
>> node 1 cpus: 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47
>> node 1 size: 64509 MB
>> node 1 free: 63942 MB
>> node 2 cpus: 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71
>> node 2 size: 64509 MB
>> node 2 free: 63056 MB
>> node 3 cpus: 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95
>> node 3 size: 63997 MB
>> node 3 free: 63420 MB
>> node distances:
>> node 0 1 2 3
>> 0: 10 16 32 33
>> 1: 16 10 25 32
>> 2: 32 25 10 16
>> 3: 33 32 16 10
>>
>> We perform PS (parameter server) business test, the behavior of the
>> service is that the client initiates a request through the network card,
>> the server responds to the request after calculation. When two PS
>> processes run on node2 and node3 separately and the network card is
>> located on 'node2' which is in cpu1, the performance of node2 (26W QPS)
>> and node3 (22W QPS) is different.
>> It is better that the NIC queues are bound to the cpu1 cores in turn,
>> then XPS will also be properly initialized, while cpumask_local_spread
>> only considers the local node. When the number of NIC queues exceeds the
>> number of cores in the local node, it returns to the online core directly.
>> So when PS runs on node3 sending a calculated request, the performance is
>> not as good as the node2.
>> The IRQ from 369-392 will be bound from NUMA node0 to NUMA node3 with this
>> patch, before the patch:
>> Euler:/sys/bus/pci # cat /proc/irq/369/smp_affinity_list
>> 0
>> Euler:/sys/bus/pci # cat /proc/irq/370/smp_affinity_list
>> 1
>> ...
>> Euler:/sys/bus/pci # cat /proc/irq/391/smp_affinity_list
>> 22
>> Euler:/sys/bus/pci # cat /proc/irq/392/smp_affinity_list
>> 23
>> After the patch:
>> Euler:/sys/bus/pci # cat /proc/irq/369/smp_affinity_list
>> 72
>> Euler:/sys/bus/pci # cat /proc/irq/370/smp_affinity_list
>> 73
>> ...
>> Euler:/sys/bus/pci # cat /proc/irq/391/smp_affinity_list
>> 94
>> Euler:/sys/bus/pci # cat /proc/irq/392/smp_affinity_list
>> 95
>> So the performance of the node3 is the same as node2 that is 26W QPS when
>> the network card is still in 'node2' with the patch.
>>
>> It is considered that the NIC and other I/O devices shall initialize the
>> interrupt binding, if the cores of the local node are used up, it is
>> reasonable to return the node closest to it. Let's optimize it and find
>> the nearest node through NUMA distance for the non-local NUMA nodes.
>
> As I've said/asked earlier. I am missing some background how this is
> affecting other existing users. Is this just that nobody has noticed the

I appreciate yours question, but I can't answer 'YES' or 'NO' to it. Since
I encountered this issue, I'm glad to discuss this in the community. If we
can solve it, it can give gain for people who maybe spend time to spot it
again.

> suboptimal cpu usage or is your workload very special in that regards.

What I have done is just that choosing cpu core from the nearest non-local
NUMA node, not the random online cpu core when the local cpu core is used
up. It's no matter what the workload is, Why I mention the PS in the patch?
Because this issue is triggered by it.

Thanks,
Shaokun

>
>> Cc: Andrew Morton <akpm@linux-foundation.org>
>> Cc: Juergen Gross <jgross@suse.com>
>> Cc: Paul Burton <paul.burton@mips.com>
>> Cc: Michal Hocko <mhocko@suse.com>
>> Cc: Michael Ellerman <mpe@ellerman.id.au>
>> Cc: Mike Rapoport <rppt@linux.ibm.com>
>> Cc: Anshuman Khandual <anshuman.khandual@arm.com>
>> Signed-off-by: yuqi jin <jinyuqi@huawei.com>
>> Signed-off-by: Shaokun Zhang <zhangshaokun@hisilicon.com>
>> ---
>> ChangeLog from v3:
>> 1. Make spread_lock local to cpumask_local_spread();
>> 2. Add more descriptions on the affinities change in log;
>>
>> ChangeLog from v2:
>> 1. Change the variables as static and use spinlock to protect;
>> 2. Give more explantation on test and performance;
>>
>> lib/cpumask.c | 102 +++++++++++++++++++++++++++++++++++++++++++++++++++-------
>> 1 file changed, 90 insertions(+), 12 deletions(-)
>>
>> diff --git a/lib/cpumask.c b/lib/cpumask.c
>> index 0cb672eb107c..f7394ba36116 100644
>> --- a/lib/cpumask.c
>> +++ b/lib/cpumask.c
>> @@ -6,6 +6,7 @@
>> #include <linux/export.h>
>> #include <linux/memblock.h>
>> #include <linux/numa.h>
>> +#include <linux/spinlock.h>
>>
>> /**
>> * cpumask_next - get the next cpu in a cpumask
>> @@ -192,18 +193,39 @@ void __init free_bootmem_cpumask_var(cpumask_var_t mask)
>> }
>> #endif
>>
>> -/**
>> - * cpumask_local_spread - select the i'th cpu with local numa cpu's first
>> - * @i: index number
>> - * @node: local numa_node
>> - *
>> - * This function selects an online CPU according to a numa aware policy;
>> - * local cpus are returned first, followed by non-local ones, then it
>> - * wraps around.
>> - *
>> - * It's not very efficient, but useful for setup.
>> - */
>> -unsigned int cpumask_local_spread(unsigned int i, int node)
>> +static void calc_node_distance(int *node_dist, int node)
>> +{
>> + int i;
>> +
>> + for (i = 0; i < nr_node_ids; i++)
>> + node_dist[i] = node_distance(node, i);
>> +}
>> +
>> +static int find_nearest_node(int *node_dist, bool *used)
>> +{
>> + int i, min_dist = node_dist[0], node_id = -1;
>> +
>> + /* Choose the first unused node to compare */
>> + for (i = 0; i < nr_node_ids; i++) {
>> + if (used[i] == 0) {
>> + min_dist = node_dist[i];
>> + node_id = i;
>> + break;
>> + }
>> + }
>> +
>> + /* Compare and return the nearest node */
>> + for (i = 0; i < nr_node_ids; i++) {
>> + if (node_dist[i] < min_dist && used[i] == 0) {
>> + min_dist = node_dist[i];
>> + node_id = i;
>> + }
>> + }
>> +
>> + return node_id;
>> +}
>> +
>> +static unsigned int __cpumask_local_spread(unsigned int i, int node)
>> {
>> int cpu;
>>
>> @@ -231,4 +253,60 @@ unsigned int cpumask_local_spread(unsigned int i, int node)
>> }
>> BUG();
>> }
>> +
>> +/**
>> + * cpumask_local_spread - select the i'th cpu with local numa cpu's first
>> + * @i: index number
>> + * @node: local numa_node
>> + *
>> + * This function selects an online CPU according to a numa aware policy;
>> + * local cpus are returned first, followed by the nearest non-local ones,
>> + * then it wraps around.
>> + *
>> + * It's not very efficient, but useful for setup.
>> + */
>> +unsigned int cpumask_local_spread(unsigned int i, int node)
>> +{
>> + static DEFINE_SPINLOCK(spread_lock);
>> + static int node_dist[MAX_NUMNODES];
>> + static bool used[MAX_NUMNODES];
>> + unsigned long flags;
>> + int cpu, j, id;
>> +
>> + /* Wrap: we always want a cpu. */
>> + i %= num_online_cpus();
>> +
>> + if (node == NUMA_NO_NODE) {
>> + for_each_cpu(cpu, cpu_online_mask)
>> + if (i-- == 0)
>> + return cpu;
>> + } else {
>> + if (nr_node_ids > MAX_NUMNODES)
>> + return __cpumask_local_spread(i, node);
>> +
>> + spin_lock_irqsave(&spread_lock, flags);
>> + memset(used, 0, nr_node_ids * sizeof(bool));
>> + calc_node_distance(node_dist, node);
>> + for (j = 0; j < nr_node_ids; j++) {
>> + id = find_nearest_node(node_dist, used);
>> + if (id < 0)
>> + break;
>> +
>> + for_each_cpu_and(cpu, cpumask_of_node(id),
>> + cpu_online_mask)
>> + if (i-- == 0) {
>> + spin_unlock_irqrestore(&spread_lock,
>> + flags);
>> + return cpu;
>> + }
>> + used[id] = 1;
>> + }
>> + spin_unlock_irqrestore(&spread_lock, flags);
>> +
>> + for_each_cpu(cpu, cpu_online_mask)
>> + if (i-- == 0)
>> + return cpu;
>> + }
>> + BUG();
>> +}
>> EXPORT_SYMBOL(cpumask_local_spread);
>> --
>> 2.7.4
>

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