linux-kernel - Re: [PATCH v11 9/9] cpuset: Allow reporting of sched domain generation info

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Date:   Thu, 19 Jul 2018 15:54:29 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Waiman Long <longman@...hat.com>
Cc:     Tejun Heo <tj@...nel.org>, Li Zefan <lizefan@...wei.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Ingo Molnar <mingo@...hat.com>, cgroups@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
        kernel-team@...com, pjt@...gle.com, luto@...capital.net,
        Mike Galbraith <efault@....de>, torvalds@...ux-foundation.org,
        Roman Gushchin <guro@...com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Patrick Bellasi <patrick.bellasi@....com>
Subject: Re: [PATCH v11 9/9] cpuset: Allow reporting of sched domain
 generation info

On Sun, Jun 24, 2018 at 03:30:40PM +0800, Waiman Long wrote:
> This patch enables us to report sched domain generation information.
> 
> If DYNAMIC_DEBUG is enabled, issuing the following command
> 
>   echo "file cpuset.c +p" > /sys/kernel/debug/dynamic_debug/control
> 
> and setting loglevel to 8 will allow the kernel to show what scheduling
> domain changes are being made.
> 
> Signed-off-by: Waiman Long <longman@...hat.com>
> ---
>  kernel/cgroup/cpuset.c | 18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
> 
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index 07a5575..62b7e61 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -836,6 +836,23 @@ static int generate_sched_domains(cpumask_var_t **domains,
>  	return ndoms;
>  }
>  
> +#ifdef CONFIG_DEBUG_KERNEL
> +static inline void debug_print_domains(cpumask_var_t *doms, int ndoms)
> +{
> +	int i;
> +	char buf[200];
> +	char *ptr, *end = buf + sizeof(buf) - 1;
> +
> +	for (i = 0, ptr = buf, *end = '\0'; i < ndoms; i++)
> +		ptr += snprintf(ptr, end - ptr, "dom%d=%*pbl ", i,
> +				cpumask_pr_args(doms[i]));
> +
> +	pr_debug("Generated %d domains: %s\n", ndoms, buf);
> +}
> +#else
> +static inline void debug_print_domains(cpumask_var_t *doms, int ndoms) { }
> +#endif

I still hate this patch.. it prints information already available in
sched_debug and has that rediculous on-stack buffer.