From: Michal Hocko <mhocko@kernel.org>
To: Shaokun Zhang <zhangshaokun@hisilicon.com>
Cc: linux-kernel@vger.kernel.org, yuqi jin <jinyuqi@huawei.com>,
Andrew Morton <akpm@linux-foundation.org>,
Mike Rapoport <rppt@linux.ibm.com>,
Paul Burton <paul.burton@mips.com>,
Michael Ellerman <mpe@ellerman.id.au>,
Anshuman Khandual <anshuman.khandual@arm.com>
Subject: Re: [PATCH v2] lib: optimize cpumask_local_spread()
Date: Tue, 5 Nov 2019 08:01:41 +0100 [thread overview]
Message-ID: <20191105070141.GF22672@dhcp22.suse.cz> (raw)
In-Reply-To: <1572863268-28585-1-git-send-email-zhangshaokun@hisilicon.com>
On Mon 04-11-19 18:27:48, Shaokun Zhang wrote:
> From: yuqi jin <jinyuqi@huawei.com>
>
> In the multi-processor and NUMA system, I/O 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, instead
> of choosing any online cpu immediately.
>
> For the current code, it only considers the local NUMA node and it
> doesn't compute the distances between different NUMA nodes for the
> non-local NUMA nodes. Let's optimize it and find the nearest node
> through NUMA distance. The performance will be better if it return
> the nearest node than the random node.
Numbers please
[...]
> +/**
> + * 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)
> +{
> + int node_dist[MAX_NUMNODES] = {0};
> + bool used[MAX_NUMNODES] = {0};
Ugh. This might be a lot of stack space. Some distro kernels use large
NODE_SHIFT (e.g 10 so this would be 4kB of stack space just for the
node_dist).
> + int cpu, j, id;
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2019-11-05 7:01 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-04 10:27 [PATCH v2] lib: optimize cpumask_local_spread() Shaokun Zhang
2019-11-05 7:01 ` Michal Hocko [this message]
2019-11-06 1:33 ` Andrew Morton
2019-11-06 2:49 ` Shaokun Zhang
2019-11-06 7:17 ` Michal Hocko
2019-11-06 8:02 ` Shaokun Zhang
2019-11-06 9:22 ` Michal Hocko
2019-11-07 1:48 ` Shaokun Zhang
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