linux-kernel - Re: [PATCH 2/2] cpusets,isolcpus: add file to show isolated cpus in cpuset

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Date:	Tue, 24 Feb 2015 18:15:16 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Rik van Riel <riel@...hat.com>
cc:	linux-kernel@...r.kernel.org,
	Peter Zijlstra <peterz@...radead.org>,
	Clark Williams <williams@...hat.com>,
	Li Zefan <lizefan@...wei.com>, Ingo Molnar <mingo@...hat.com>,
	Luiz Capitulino <lcapitulino@...hat.com>,
	cgroups@...r.kernel.org
Subject: Re: [PATCH 2/2] cpusets,isolcpus: add file to show isolated cpus in
 cpuset

On Mon, 23 Feb 2015, riel@...hat.com wrote:

> From: Rik van Riel <riel@...hat.com>
> 
> The previous patch makes it so the code skips over isolcpus when
> building scheduler load balancing domains. This makes it hard to
> see for a user which of the CPUs in a cpuset are participating in
> load balancing, and which ones are isolated cpus.
> 
> Add a cpuset.isolcpus file with info on which cpus in a cpuset are
> isolated CPUs.
> 
> This file is read-only for now. In the future we could extend things
> so isolcpus can be changed at run time, for the root (system wide)
> cpuset only.
> 
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Clark Williams <williams@...hat.com>
> Cc: Li Zefan <lizefan@...wei.com>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Luiz Capitulino <lcapitulino@...hat.com>
> Cc: cgroups@...r.kernel.org
> Signed-off-by: Rik van Riel <riel@...hat.com>
> ---
>  kernel/cpuset.c | 27 +++++++++++++++++++++++++++
>  1 file changed, 27 insertions(+)
> 
> diff --git a/kernel/cpuset.c b/kernel/cpuset.c
> index 1ad63fa37cb4..19ad5d3377f8 100644
> --- a/kernel/cpuset.c
> +++ b/kernel/cpuset.c
> @@ -1563,6 +1563,7 @@ typedef enum {
>  	FILE_MEMORY_PRESSURE,
>  	FILE_SPREAD_PAGE,
>  	FILE_SPREAD_SLAB,
> +	FILE_ISOLCPUS,
>  } cpuset_filetype_t;
>  
>  static int cpuset_write_u64(struct cgroup_subsys_state *css, struct cftype *cft,
> @@ -1704,6 +1705,23 @@ static ssize_t cpuset_write_resmask(struct kernfs_open_file *of,
>  	return retval ?: nbytes;
>  }
>  
> +static size_t cpuset_sprintf_isolcpus(char *s, ssize_t pos, struct cpuset *cs)
> +{
> +	cpumask_var_t my_isolated_cpus;
> +	ssize_t count;
> +	

Whitespace.

> +	if (!alloc_cpumask_var(&my_isolated_cpus, GFP_KERNEL))
> +		return 0;
> +
> +	cpumask_and(my_isolated_cpus, cs->cpus_allowed, cpu_isolated_map);
> +
> +	count = cpulist_scnprintf(s, pos, my_isolated_cpus);
> +
> +	free_cpumask_var(my_isolated_cpus);
> +
> +	return count;
> +}
> +
>  /*
>   * These ascii lists should be read in a single call, by using a user
>   * buffer large enough to hold the entire map.  If read in smaller
> @@ -1738,6 +1756,9 @@ static int cpuset_common_seq_show(struct seq_file *sf, void *v)
>  	case FILE_EFFECTIVE_MEMLIST:
>  		s += nodelist_scnprintf(s, count, cs->effective_mems);
>  		break;
> +	case FILE_ISOLCPUS:
> +		s += cpuset_sprintf_isolcpus(s, count, cs);
> +		break;

This patch looks fine, and I think cpuset.effective_cpus and 
cpuset.isolcpus can be used well together, but will need updating now that 
commit e8e6d97c9b ("cpuset: use %*pb[l] to print bitmaps including 
cpumasks and nodemasks") has been merged which reworks this function.

It's a little unfortunate, though, that the user sees Cpus_allowed, 
cpuset.cpus, and cpuset.effective_cpus that include isolcpus and then have 
to check another cpulist for the isolcpus to see their sched domain, 
though.

>  	default:
>  		ret = -EINVAL;
>  		goto out_unlock;
> @@ -1906,6 +1927,12 @@ static struct cftype files[] = {
>  		.private = FILE_MEMORY_PRESSURE_ENABLED,
>  	},
>  
> +	{
> +		.name = "isolcpus",
> +		.seq_show = cpuset_common_seq_show,
> +		.private = FILE_ISOLCPUS,
> +	},
> +
>  	{ }	/* terminate */
>  };
>  
--
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