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Message-ID: <176907693853.510.6603938718127476691.tip-bot2@tip-bot2>
Date: Thu, 22 Jan 2026 10:15:38 -0000
From: "tip-bot2 for Peter Zijlstra" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: "Peter Zijlstra (Intel)" <peterz@...radead.org>, x86@...nel.org,
linux-kernel@...r.kernel.org
Subject: [tip: sched/core] rseq: Move slice_ext_nsec to debugfs
The following commit has been merged into the sched/core branch of tip:
Commit-ID: e1d7f54900f1e1d3003a85b78cd7105a64203ff7
Gitweb: https://git.kernel.org/tip/e1d7f54900f1e1d3003a85b78cd7105a64203ff7
Author: Peter Zijlstra <peterz@...radead.org>
AuthorDate: Wed, 21 Jan 2026 14:21:51 +01:00
Committer: Peter Zijlstra <peterz@...radead.org>
CommitterDate: Thu, 22 Jan 2026 11:11:20 +01:00
rseq: Move slice_ext_nsec to debugfs
Move changing the slice ext duration to debugfs, a sliglty less permanent
interface.
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Link: https://patch.msgid.link/20260121143207.923520192@infradead.org
---
Documentation/admin-guide/sysctl/kernel.rst | 11 +---
Documentation/userspace-api/rseq.rst | 4 +-
kernel/rseq.c | 69 +++++++++++++-------
3 files changed, 49 insertions(+), 35 deletions(-)
diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/admin-guide/sysctl/kernel.rst
index b09d18e..239da22 100644
--- a/Documentation/admin-guide/sysctl/kernel.rst
+++ b/Documentation/admin-guide/sysctl/kernel.rst
@@ -1248,17 +1248,6 @@ reboot-cmd (SPARC only)
ROM/Flash boot loader. Maybe to tell it what to do after
rebooting. ???
-rseq_slice_extension_nsec
-=========================
-
-A task can request to delay its scheduling if it is in a critical section
-via the prctl(PR_RSEQ_SLICE_EXTENSION_SET) mechanism. This sets the maximum
-allowed extension in nanoseconds before scheduling of the task is enforced.
-Default value is 10000ns (10us). The possible range is 10000ns (10us) to
-50000ns (50us).
-
-This value has a direct correlation to the worst case scheduling latency;
-increment at your own risk.
sched_energy_aware
==================
diff --git a/Documentation/userspace-api/rseq.rst b/Documentation/userspace-api/rseq.rst
index e1fdb0d..29af6c3 100644
--- a/Documentation/userspace-api/rseq.rst
+++ b/Documentation/userspace-api/rseq.rst
@@ -79,7 +79,9 @@ slice extension by setting rseq::slice_ctrl::request to 1. If the thread is
interrupted and the interrupt results in a reschedule request in the
kernel, then the kernel can grant a time slice extension and return to
userspace instead of scheduling out. The length of the extension is
-determined by the ``rseq_slice_extension_nsec`` sysctl.
+determined by debugfs:rseq/slice_ext_nsec. The default value is 10 usec; which
+is the minimum value. It can be incremented to 50 usecs, however doing so
+can/will affect the minimum scheduling latency.
The kernel indicates the grant by clearing rseq::slice_ctrl::request and
setting rseq::slice_ctrl::granted to 1. If there is a reschedule of the
diff --git a/kernel/rseq.c b/kernel/rseq.c
index 1c5490a..e423a9b 100644
--- a/kernel/rseq.c
+++ b/kernel/rseq.c
@@ -123,7 +123,6 @@ void __rseq_trace_ip_fixup(unsigned long ip, unsigned long start_ip,
}
#endif /* CONFIG_TRACEPOINTS */
-#ifdef CONFIG_DEBUG_FS
#ifdef CONFIG_RSEQ_STATS
DEFINE_PER_CPU(struct rseq_stats, rseq_stats);
@@ -222,16 +221,19 @@ static const struct file_operations debug_ops = {
.release = single_release,
};
+static void rseq_slice_ext_init(struct dentry *root_dir);
+
static int __init rseq_debugfs_init(void)
{
struct dentry *root_dir = debugfs_create_dir("rseq", NULL);
debugfs_create_file("debug", 0644, root_dir, NULL, &debug_ops);
rseq_stats_init(root_dir);
+ if (IS_ENABLED(CONFIG_RSEQ_SLICE_EXTENSION))
+ rseq_slice_ext_init(root_dir);
return 0;
}
__initcall(rseq_debugfs_init);
-#endif /* CONFIG_DEBUG_FS */
static bool rseq_set_ids(struct task_struct *t, struct rseq_ids *ids, u32 node_id)
{
@@ -515,7 +517,9 @@ struct slice_timer {
void *cookie;
};
-unsigned int rseq_slice_ext_nsecs __read_mostly = 10 * NSEC_PER_USEC;
+static const unsigned int rseq_slice_ext_nsecs_min = 10 * NSEC_PER_USEC;
+static const unsigned int rseq_slice_ext_nsecs_max = 50 * NSEC_PER_USEC;
+unsigned int rseq_slice_ext_nsecs __read_mostly = rseq_slice_ext_nsecs_min;
static DEFINE_PER_CPU(struct slice_timer, slice_timer);
DEFINE_STATIC_KEY_TRUE(rseq_slice_extension_key);
@@ -761,30 +765,48 @@ SYSCALL_DEFINE0(rseq_slice_yield)
return yielded;
}
-#ifdef CONFIG_SYSCTL
-static const unsigned int rseq_slice_ext_nsecs_min = 10 * NSEC_PER_USEC;
-static const unsigned int rseq_slice_ext_nsecs_max = 50 * NSEC_PER_USEC;
+static int rseq_slice_ext_show(struct seq_file *m, void *p)
+{
+ seq_printf(m, "%d\n", rseq_slice_ext_nsecs);
+ return 0;
+}
+
+static ssize_t rseq_slice_ext_write(struct file *file, const char __user *ubuf,
+ size_t count, loff_t *ppos)
+{
+ unsigned int nsecs;
+
+ if (kstrtouint_from_user(ubuf, count, 10, &nsecs))
+ return -EINVAL;
+
+ if (nsecs < rseq_slice_ext_nsecs_min)
+ return -ERANGE;
-static const struct ctl_table rseq_slice_ext_sysctl[] = {
- {
- .procname = "rseq_slice_extension_nsec",
- .data = &rseq_slice_ext_nsecs,
- .maxlen = sizeof(unsigned int),
- .mode = 0644,
- .proc_handler = proc_douintvec_minmax,
- .extra1 = (unsigned int *)&rseq_slice_ext_nsecs_min,
- .extra2 = (unsigned int *)&rseq_slice_ext_nsecs_max,
- },
+ if (nsecs > rseq_slice_ext_nsecs_max)
+ return -ERANGE;
+
+ rseq_slice_ext_nsecs = nsecs;
+
+ return count;
+}
+
+static int rseq_slice_ext_open(struct inode *inode, struct file *file)
+{
+ return single_open(file, rseq_slice_ext_show, inode->i_private);
+}
+
+static const struct file_operations slice_ext_ops = {
+ .open = rseq_slice_ext_open,
+ .read = seq_read,
+ .write = rseq_slice_ext_write,
+ .llseek = seq_lseek,
+ .release = single_release,
};
-static void rseq_slice_sysctl_init(void)
+static void rseq_slice_ext_init(struct dentry *root_dir)
{
- if (rseq_slice_extension_enabled())
- register_sysctl_init("kernel", rseq_slice_ext_sysctl);
+ debugfs_create_file("slice_ext_nsec", 0644, root_dir, NULL, &slice_ext_ops);
}
-#else /* CONFIG_SYSCTL */
-static inline void rseq_slice_sysctl_init(void) { }
-#endif /* !CONFIG_SYSCTL */
static int __init rseq_slice_cmdline(char *str)
{
@@ -807,8 +829,9 @@ static int __init rseq_slice_init(void)
hrtimer_setup(per_cpu_ptr(&slice_timer.timer, cpu), rseq_slice_expired,
CLOCK_MONOTONIC, HRTIMER_MODE_REL_PINNED_HARD);
}
- rseq_slice_sysctl_init();
return 0;
}
device_initcall(rseq_slice_init);
+#else
+static void rseq_slice_ext_init(struct dentry *root_dir) { }
#endif /* CONFIG_RSEQ_SLICE_EXTENSION */
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