linux-kernel - [RFC PATCH 2/2] workqueue: update sysfs handlers, allow setting RT policies

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Message-Id: <20220323145600.2156689-3-linux@rasmusvillemoes.dk>
Date:   Wed, 23 Mar 2022 15:56:00 +0100
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     Tejun Heo <tj@...nel.org>, Lai Jiangshan <jiangshanlai@...il.com>
Cc:     André Pribil <a.pribil@...k-ipc.com>,
        Steven Walter <stevenrwalter@...il.com>,
        Oleksij Rempel <o.rempel@...gutronix.de>,
        Esben Haabendal <esben@...nix.com>,
        Jiri Slaby <jirislaby@...nel.org>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Peter Hurley <peter@...leysoftware.com>,
        linux-rt-users@...r.kernel.org,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        linux-kernel@...r.kernel.org
Subject: [RFC PATCH 2/2] workqueue: update sysfs handlers, allow setting RT policies

For this POC, this (ab)uses the "nice" attribute.

It's of course not exactly pretty, but it avoids the problem of "what
to show in the xyz file when using SCHED_NORMAL, and what to show in
the nice file when using SCHED_RR/SCHED_FIFO".

It's backwards-compatible, in that a bare integer is interpreted as a
nice value, while an integer prefixed by "fifo:" or "rr:" chooses that
RT scheduling policy with the associated value as the priority. The
show method of course reflects what the store method accepts.

Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>
---
 kernel/workqueue.c | 54 ++++++++++++++++++++++++++++++++++++++++------
 1 file changed, 47 insertions(+), 7 deletions(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 9eb2ff7bcc04..a97f1aff809e 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -5538,13 +5538,34 @@ static ssize_t wq_nice_show(struct device *dev, struct device_attribute *attr,
 			    char *buf)
 {
 	struct workqueue_struct *wq = dev_to_wq(dev);
-	int written;
+	struct workqueue_attrs *wqattrs;
+	const char *pfx;
+	int val;
 
 	mutex_lock(&wq->mutex);
-	written = scnprintf(buf, PAGE_SIZE, "%d\n", wq->unbound_attrs->nice);
+	wqattrs = wq->unbound_attrs;
+	switch (wqattrs->policy) {
+	case SCHED_NORMAL:
+		pfx = "";
+		val = wqattrs->nice;
+		break;
+	case SCHED_FIFO:
+		pfx = "fifo:";
+		val = wqattrs->priority;
+		break;
+	case SCHED_RR:
+		pfx = "rr:";
+		val = wqattrs->priority;
+		break;
+	default:
+		/* Shouldn't happen. */
+		pfx = NULL;
+	}
 	mutex_unlock(&wq->mutex);
 
-	return written;
+	if (!pfx)
+		return -EIO;
+	return scnprintf(buf, PAGE_SIZE, "%s%d\n", pfx, val);
 }
 
 /* prepare workqueue_attrs for sysfs store operations */
@@ -5568,6 +5589,24 @@ static ssize_t wq_nice_store(struct device *dev, struct device_attribute *attr,
 	struct workqueue_struct *wq = dev_to_wq(dev);
 	struct workqueue_attrs *attrs;
 	int ret = -ENOMEM;
+	int policy, val;
+
+	if (sscanf(buf, "fifo:%d", &val) == 1)
+		policy = SCHED_FIFO;
+	else if (sscanf(buf, "rr:%d", &val) == 1)
+		policy = SCHED_RR;
+	else if (sscanf(buf, "%d", &val) == 1)
+		policy = SCHED_NORMAL;
+	else
+		return -EINVAL;
+
+	if (policy == SCHED_NORMAL) {
+		if (val < MIN_NICE || val > MAX_NICE)
+			return -EINVAL;
+	} else {
+		if (val <= 0 || val >= MAX_RT_PRIO)
+			return -EINVAL;
+	}
 
 	apply_wqattrs_lock();
 
@@ -5575,11 +5614,12 @@ static ssize_t wq_nice_store(struct device *dev, struct device_attribute *attr,
 	if (!attrs)
 		goto out_unlock;
 
-	if (sscanf(buf, "%d", &attrs->nice) == 1 &&
-	    attrs->nice >= MIN_NICE && attrs->nice <= MAX_NICE)
-		ret = apply_workqueue_attrs_locked(wq, attrs);
+	attrs->policy = policy;
+	if (policy == SCHED_NORMAL)
+		attrs->nice = val;
 	else
-		ret = -EINVAL;
+		attrs->priority = val;
+	ret = apply_workqueue_attrs_locked(wq, attrs);
 
 out_unlock:
 	apply_wqattrs_unlock();
-- 
2.31.1