linux-kernel - Re: [PATCH v5 7/7] sched/fair: Fair server interface

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Date:   Tue, 7 Nov 2023 13:38:18 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Daniel Bristot de Oliveira <bristot@...nel.org>
Cc:     Ingo Molnar <mingo@...hat.com>, Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Valentin Schneider <vschneid@...hat.com>,
        linux-kernel@...r.kernel.org,
        Luca Abeni <luca.abeni@...tannapisa.it>,
        Tommaso Cucinotta <tommaso.cucinotta@...tannapisa.it>,
        Thomas Gleixner <tglx@...utronix.de>,
        Joel Fernandes <joel@...lfernandes.org>,
        Vineeth Pillai <vineeth@...byteword.org>,
        Shuah Khan <skhan@...uxfoundation.org>,
        Phil Auld <pauld@...hat.com>
Subject: Re: [PATCH v5 7/7] sched/fair: Fair server interface

On Sat, Nov 04, 2023 at 11:59:24AM +0100, Daniel Bristot de Oliveira wrote:
> Add an interface for fair server setup on debugfs.
> 
> Each rq have three files under /sys/kernel/debug/sched/rq/CPU{ID}:
> 
>  - fair_server_runtime: set runtime in ns
>  - fair_server_period: set period in ns
>  - fair_server_defer: on/off for the defer mechanism
> 
> Signed-off-by: Daniel Bristot de Oliveira <bristot@...nel.org>
> ---

I did the below, that gives us:

/debug/sched/fair_server/cpuX/{runtime,period,defer}

I wanted to also add:

/debug/sched/fair_server/{runtime,period,defer}

to more easily set all CPUs to the same value, but then figured
userspace will just have to loop.

---

--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -380,10 +380,10 @@ static ssize_t sched_fair_server_write(s
 			break;
 		}
 
-		if (runtime > period
-				|| period > fair_server_period_max
-				|| period < fair_server_period_min
-				|| zerolax > 1) {
+		if (runtime > period ||
+		    period > fair_server_period_max ||
+		    period < fair_server_period_min ||
+		    zerolax > 1) {
 			cnt = -EINVAL;
 			goto out;
 		}
@@ -515,11 +515,11 @@ static struct dentry *debugfs_sched;
 
 static void debugfs_fair_server_init(void)
 {
-	long cpu;
-	struct dentry *rq_dentry;
+	struct dentry *d_fair;
+	unsigned int cpu;
 
-	rq_dentry = debugfs_create_dir("rq", debugfs_sched);
-	if (!rq_dentry)
+	d_fair = debugfs_create_dir("fair_server", debugfs_sched);
+	if (!d_fair)
 		return;
 
 	for_each_possible_cpu(cpu) {
@@ -527,11 +527,11 @@ static void debugfs_fair_server_init(voi
 		char buf[32];
 
 		snprintf(buf, sizeof(buf), "cpu%ld", cpu);
-		d_cpu = debugfs_create_dir(buf, rq_dentry);
+		d_cpu = debugfs_create_dir(buf, d_fair);
 
-		debugfs_create_file("fair_server_runtime", 0644, d_cpu, (void *) cpu, &fair_server_runtime_fops);
-		debugfs_create_file("fair_server_period", 0644, d_cpu, (void *) cpu, &fair_server_period_fops);
-		debugfs_create_file("fair_server_defer", 0644, d_cpu, (void *) cpu, &fair_server_defer_fops);
+		debugfs_create_file("runtime", 0644, d_cpu, (void *) cpu, &fair_server_runtime_fops);
+		debugfs_create_file("period", 0644, d_cpu, (void *) cpu, &fair_server_period_fops);
+		debugfs_create_file("defer", 0644, d_cpu, (void *) cpu, &fair_server_defer_fops);
 	}
 }