linux-kernel - Re: [Patch v4 1/3] lib: Restrict cpumask_local

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Date:   Mon, 29 Jun 2020 12:11:25 -0400
From:   Nitesh Narayan Lal <nitesh@...hat.com>
To:     linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
        peterz@...radead.org
Cc:     frederic@...nel.org, mtosatti@...hat.com, juri.lelli@...hat.com,
        abelits@...vell.com, bhelgaas@...gle.com,
        linux-pci@...r.kernel.org, rostedt@...dmis.org, mingo@...nel.org,
        tglx@...utronix.de, davem@...emloft.net, akpm@...ux-foundation.org,
        sfr@...b.auug.org.au, stephen@...workplumber.org,
        rppt@...ux.vnet.ibm.com, jinyuqi@...wei.com,
        zhangshaokun@...ilicon.com
Subject: Re: [Patch v4 1/3] lib: Restrict cpumask_local_spread to houskeeping
 CPUs


On 6/25/20 6:34 PM, Nitesh Narayan Lal wrote:
> From: Alex Belits <abelits@...vell.com>
>
> The current implementation of cpumask_local_spread() does not respect the
> isolated CPUs, i.e., even if a CPU has been isolated for Real-Time task,
> it will return it to the caller for pinning of its IRQ threads. Having
> these unwanted IRQ threads on an isolated CPU adds up to a latency
> overhead.
>
> Restrict the CPUs that are returned for spreading IRQs only to the
> available housekeeping CPUs.
>
> Signed-off-by: Alex Belits <abelits@...vell.com>
> Signed-off-by: Nitesh Narayan Lal <nitesh@...hat.com>

Hi Peter,

I just realized that Yuqi jin's patch [1] that modifies cpumask_local_spread is
lying in linux-next.
Should I do a re-post by re-basing the patches on the top of linux-next?

[1]
https://lore.kernel.org/lkml/1582768688-2314-1-git-send-email-zhangshaokun@hisilicon.com/

> ---
>  lib/cpumask.c | 16 +++++++++++-----
>  1 file changed, 11 insertions(+), 5 deletions(-)
>
> diff --git a/lib/cpumask.c b/lib/cpumask.c
> index fb22fb266f93..85da6ab4fbb5 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/sched/isolation.h>
>  
>  /**
>   * cpumask_next - get the next cpu in a cpumask
> @@ -205,22 +206,27 @@ void __init free_bootmem_cpumask_var(cpumask_var_t mask)
>   */
>  unsigned int cpumask_local_spread(unsigned int i, int node)
>  {
> -	int cpu;
> +	int cpu, hk_flags;
> +	const struct cpumask *mask;
>  
> +	hk_flags = HK_FLAG_DOMAIN | HK_FLAG_MANAGED_IRQ;
> +	mask = housekeeping_cpumask(hk_flags);
>  	/* Wrap: we always want a cpu. */
> -	i %= num_online_cpus();
> +	i %= cpumask_weight(mask);
>  
>  	if (node == NUMA_NO_NODE) {
> -		for_each_cpu(cpu, cpu_online_mask)
> +		for_each_cpu(cpu, mask) {
>  			if (i-- == 0)
>  				return cpu;
> +		}
>  	} else {
>  		/* NUMA first. */
> -		for_each_cpu_and(cpu, cpumask_of_node(node), cpu_online_mask)
> +		for_each_cpu_and(cpu, cpumask_of_node(node), mask) {
>  			if (i-- == 0)
>  				return cpu;
> +		}
>  
> -		for_each_cpu(cpu, cpu_online_mask) {
> +		for_each_cpu(cpu, mask) {
>  			/* Skip NUMA nodes, done above. */
>  			if (cpumask_test_cpu(cpu, cpumask_of_node(node)))
>  				continue;
-- 
Nitesh



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