Messages in this thread | | | Date | Thu, 31 Oct 2019 17:37:21 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH] lib: optimize cpumask_local_spread() |
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On Thu, 31 Oct 2019 14:03:33 +0800 Shaokun Zhang <zhangshaokun@hisilicon.com> wrote:
> From: yuqi jin <jinyuqi@huawei.com> > > In the multi-processor and NUMA system, A device may have many numa > nodes belonging to multiple cpus. When we get a local numa, it is better > to find the node closest to the local numa node to return instead of > going to the online cpu immediately. > > For example, In Huawei Kunpeng 920 system, there are 4 NUMA node(0 -3) > in the 2-socket system(0 - 1). If the I/O device is in socket1 > and the local NUMA node is 2, we shall choose the non-local node3 in > the same socket when cpu core in NUMA node2 is less that I/O requirements. > If we directly pick one cpu core from all online ones, it may be in > the another socket and it is not friendly for performance. > > ... > > Changes from RFC: > Address Michal Hocko's comment: Use GFP_ATOMIC instead of GFP_KERNEL
Are you sure this is necessary? cpumask_local_spread() is typically called when a device driver is initializing irq affinities, and sleeping allocations are usually OK at driver initialization time. If there is some driver which is calling cpumask_local_spread() from atomic context, I bet it's pretty easy to fix.
> --- a/lib/cpumask.c > +++ b/lib/cpumask.c > @@ -192,6 +192,33 @@ void __init free_bootmem_cpumask_var(cpumask_var_t mask) > } > #endif > > +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_flag)
The name "used_flag" is rather redundant for a thing of type bool - we know it's a flag! "used" would suffice.
> +{ > + int i, min_dist = node_dist[0], node_id = -1; > + > + for (i = 0; i < nr_node_ids; i++) > + if (used_flag[i] == 0) { > + min_dist = node_dist[i]; > + node_id = i; > + break; > + } > + for (i = 0; i < nr_node_ids; i++) > + if (node_dist[i] < min_dist && used_flag[i] == 0) { > + min_dist = node_dist[i]; > + node_id = i; > + } > + > + return node_id; > +} > + > /** > * cpumask_local_spread - select the i'th cpu with local numa cpu's first > * @i: index number > @@ -205,7 +232,8 @@ void __init free_bootmem_cpumask_var(cpumask_var_t mask) > */ > unsigned int cpumask_local_spread(unsigned int i, int node)
Yes, this has become quite an expensive function. That seems harmless given the typical callsites.
> { > - int cpu; > + int cpu, j, id, *node_dist; > + bool *used_flag; > > /* Wrap: we always want a cpu. */ > i %= num_online_cpus(); > @@ -215,19 +243,45 @@ unsigned int cpumask_local_spread(unsigned int i, int node) > if (i-- == 0) > return cpu; > } else { > - /* NUMA first. */ > - for_each_cpu_and(cpu, cpumask_of_node(node), cpu_online_mask) > - if (i-- == 0) > - return cpu; > + node_dist = kmalloc_array(nr_node_ids, sizeof(int), GFP_ATOMIC); > + if (!node_dist) > + for_each_cpu(cpu, cpu_online_mask) > + if (i-- == 0) > + return cpu; > > - for_each_cpu(cpu, cpu_online_mask) { > - /* Skip NUMA nodes, done above. */ > - if (cpumask_test_cpu(cpu, cpumask_of_node(node))) > - continue; > + used_flag = kmalloc_array(nr_node_ids, sizeof(bool), GFP_ATOMIC);
This could actually be an array of bits (include/linux/bitmap.h), but it hardly seems important.
In fact with CONFIG_NODES_SHIFT <= 10, such a bitmap would have max size of 128 bytes and could be a local. But again, this is unimportant as long as the other kmalloc is in there.
> + if (!used_flag) > + for_each_cpu(cpu, cpu_online_mask) > + if (i-- == 0) { > + kfree(node_dist); > + return cpu; > + } > + memset(used_flag, 0, nr_node_ids * sizeof(bool)); > > - if (i-- == 0) > - return cpu; > + calc_node_distance(node_dist, node); > + for (j = 0; j < nr_node_ids; j++) { > + id = find_nearest_node(node_dist, used_flag); > + if (id < 0) > + break; > + for_each_cpu_and(cpu, > + cpumask_of_node(id), cpu_online_mask) > + if (i-- == 0) { > + kfree(node_dist); > + kfree(used_flag); > + return cpu; > + } > + used_flag[id] = 1; > } > + > + for_each_cpu(cpu, cpu_online_mask) > + if (i-- == 0) { > + kfree(node_dist); > + kfree(used_flag); > + return cpu; > + } > + > + kfree(node_dist); > + kfree(used_flag); > } > BUG(); > }
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