From: Shaokun Zhang <zhangshaokun@hisilicon.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: <linux-kernel@vger.kernel.org>, yuqi jin <jinyuqi@huawei.com>,
"Mike Rapoport" <rppt@linux.ibm.com>,
Paul Burton <paul.burton@mips.com>,
"Michal Hocko" <mhocko@suse.com>,
Michael Ellerman <mpe@ellerman.id.au>,
"Anshuman Khandual" <anshuman.khandual@arm.com>
Subject: Re: [PATCH] lib: optimize cpumask_local_spread()
Date: Mon, 4 Nov 2019 14:02:47 +0800 [thread overview]
Message-ID: <cc3640e1-0e29-f196-97e4-ebf0bc8be78b@hisilicon.com> (raw)
In-Reply-To: <20191031173721.e2a40b037799a149433a4867@linux-foundation.org>
Hi Andrew,
On 2019/11/1 8:37, Andrew Morton wrote:
> 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
Got it and my limited realization, thanks for more explanations about it.
> 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.
>
Ok
>> +{
>> + 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.
>
Ok,
> 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.
>
Got it and I will follow it in next version.
Thanks,
Shaokun
>
>> + 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();
>> }
>
>
> .
>
prev parent reply other threads:[~2019-11-04 6:03 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-31 6:03 [PATCH] lib: optimize cpumask_local_spread() Shaokun Zhang
2019-10-31 7:39 ` Michal Hocko
2019-11-04 3:37 ` Shaokun Zhang
2019-11-01 0:37 ` Andrew Morton
2019-11-04 6:02 ` Shaokun Zhang [this message]
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