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Date:   Wed, 11 Dec 2019 10:08:23 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Shaokun Zhang <zhangshaokun@...ilicon.com>
Cc:     linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        yuqi jin <jinyuqi@...wei.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Juergen Gross <jgross@...e.com>,
        Paul Burton <paul.burton@...s.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Anshuman Khandual <anshuman.khandual@....com>
Subject: Re: [PATCH v4] lib: optimize cpumask_local_spread()

On Wed 11-12-19 16:03:57, Shaokun Zhang wrote:
> From: yuqi jin <jinyuqi@...wei.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
suboptimal cpu usage or is your workload very special in that regards.

> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Juergen Gross <jgross@...e.com>
> Cc: Paul Burton <paul.burton@...s.com>
> Cc: Michal Hocko <mhocko@...e.com>
> Cc: Michael Ellerman <mpe@...erman.id.au>
> Cc: Mike Rapoport <rppt@...ux.ibm.com>
> Cc: Anshuman Khandual <anshuman.khandual@....com>
> Signed-off-by: yuqi jin <jinyuqi@...wei.com>
> Signed-off-by: Shaokun Zhang <zhangshaokun@...ilicon.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

-- 
Michal Hocko
SUSE Labs

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