linux-kernel - Re: [PATCH v2] sched/debug: Put sched/domains files under the verbose flag

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Date:   Wed, 8 Feb 2023 08:26:19 -0500
From:   Phil Auld <pauld@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     gregkh@...uxfoundation.org, mingo@...hat.com, peterz@...radead.org,
        ritesh.list@...il.com, srikar@...ux.vnet.ibm.com,
        sshegde@...ux.ibm.com, vincent.guittot@...aro.org,
        vishalc@...ux.vnet.ibm.com, vschneid@...hat.com
Subject: Re: [PATCH v2] sched/debug: Put sched/domains files under the
 verbose flag

Hi Ingo, Peter,

On Fri, Jan 20, 2023 at 11:33:30AM -0500 Phil Auld wrote:
> The debug files under sched/domains can take a long time to regenerate,
> especially when updates are done one at a time. Move these files under
> the sched verbose debug flag. Allow changes to verbose to trigger
> generation of the files. This lets a user batch the updates but still
> have the information available.  The detailed topology printk messages
> are also under verbose.
> 
> Discussion that lead to this approach can be found in the link below.
> 
> Simplified code to maintain use of debugfs bool routines suggested by
> Michael Ellerman <mpe@...erman.id.au>.
> 
> Signed-off-by: Phil Auld <pauld@...hat.com>
> Cc: Michael Ellerman <mpe@...erman.id.au>
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Peter Zijlstra (Intel) <peterz@...radead.org>
> Cc: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
> Cc: Valentin Schneider <vschneid@...hat.com>
> Cc: Vishal Chourasia <vishalc@...ux.vnet.ibm.com>
> Cc: Vincent Guittot <vincent.guittot@...aro.org>
> Link: https://lore.kernel.org/all/Y01UWQL2y2r69sBX@li-05afa54c-330e-11b2-a85c-e3f3aa0db1e9.ibm.com/
> ---

Thoughts on this one?


Thanks,
Phil


> 
>  v2: fix comment typo and use cpumask_empty()
> 
>  kernel/sched/debug.c | 52 +++++++++++++++++++++++++++++++++++++++++---
>  1 file changed, 49 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
> index 1637b65ba07a..0b2340a79b65 100644
> --- a/kernel/sched/debug.c
> +++ b/kernel/sched/debug.c
> @@ -280,6 +280,45 @@ static const struct file_operations sched_dynamic_fops = {
>  
>  __read_mostly bool sched_debug_verbose;
>  
> +#ifdef CONFIG_SMP
> +static struct dentry           *sd_dentry;
> +
> +
> +static ssize_t sched_verbose_write(struct file *filp, const char __user *ubuf,
> +				  size_t cnt, loff_t *ppos)
> +{
> +	ssize_t result;
> +	bool orig;
> +
> +	cpus_read_lock();
> +	mutex_lock(&sched_domains_mutex);
> +
> +	orig = sched_debug_verbose;
> +	result = debugfs_write_file_bool(filp, ubuf, cnt, ppos);
> +
> +	if (sched_debug_verbose && !orig)
> +		update_sched_domain_debugfs();
> +	else if (!sched_debug_verbose && orig) {
> +		debugfs_remove(sd_dentry);
> +		sd_dentry = NULL;
> +	}
> +
> +	mutex_unlock(&sched_domains_mutex);
> +	cpus_read_unlock();
> +
> +	return result;
> +}
> +#else
> +#define sched_verbose_write debugfs_write_file_bool
> +#endif
> +
> +static const struct file_operations sched_verbose_fops = {
> +	.read =         debugfs_read_file_bool,
> +	.write =        sched_verbose_write,
> +	.open =         simple_open,
> +	.llseek =       default_llseek,
> +};
> +
>  static const struct seq_operations sched_debug_sops;
>  
>  static int sched_debug_open(struct inode *inode, struct file *filp)
> @@ -303,7 +342,7 @@ static __init int sched_init_debug(void)
>  	debugfs_sched = debugfs_create_dir("sched", NULL);
>  
>  	debugfs_create_file("features", 0644, debugfs_sched, NULL, &sched_feat_fops);
> -	debugfs_create_bool("verbose", 0644, debugfs_sched, &sched_debug_verbose);
> +	debugfs_create_file_unsafe("verbose", 0644, debugfs_sched, &sched_debug_verbose, &sched_verbose_fops);
>  #ifdef CONFIG_PREEMPT_DYNAMIC
>  	debugfs_create_file("preempt", 0644, debugfs_sched, NULL, &sched_dynamic_fops);
>  #endif
> @@ -345,7 +384,6 @@ late_initcall(sched_init_debug);
>  #ifdef CONFIG_SMP
>  
>  static cpumask_var_t		sd_sysctl_cpus;
> -static struct dentry		*sd_dentry;
>  
>  static int sd_flags_show(struct seq_file *m, void *v)
>  {
> @@ -402,15 +440,23 @@ void update_sched_domain_debugfs(void)
>  	if (!debugfs_sched)
>  		return;
>  
> +	if (!sched_debug_verbose)
> +		return;
> +
>  	if (!cpumask_available(sd_sysctl_cpus)) {
>  		if (!alloc_cpumask_var(&sd_sysctl_cpus, GFP_KERNEL))
>  			return;
>  		cpumask_copy(sd_sysctl_cpus, cpu_possible_mask);
>  	}
>  
> -	if (!sd_dentry)
> +	if (!sd_dentry) {
>  		sd_dentry = debugfs_create_dir("domains", debugfs_sched);
>  
> +		/* rebuild sd_sysctl_cpus if empty since it gets cleared below */
> +		if (cpumask_empty(sd_sysctl_cpus))
> +			cpumask_copy(sd_sysctl_cpus, cpu_online_mask);
> +	}
> +
>  	for_each_cpu(cpu, sd_sysctl_cpus) {
>  		struct sched_domain *sd;
>  		struct dentry *d_cpu;
> -- 
> 2.31.1
> 

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