Re: FAILED: patch "[PATCH] io_uring/sqpoll: switch away from getrusage() for CPU" failed to apply to 6.12-stable tree

[Jens Axboe <axboe@kernel.dk>]

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On 10/26/25 8:22 AM, gregkh@linuxfoundation.org wrote:
> 
> The patch below does not apply to the 6.12-stable tree.
> If someone wants it applied there, or to any other stable or longterm
> tree, then please email the backport, including the original git commit
> id to <stable@vger.kernel.org>.
> 
> To reproduce the conflict and resubmit, you may use the following commands:
> 
> git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.12.y
> git checkout FETCH_HEAD
> git cherry-pick -x 8ac9b0d33e5c0a995338ee5f25fe1b6ff7d97f65
> # <resolve conflicts, build, test, etc.>
> git commit -s
> git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2025102606-showplace-direness-c7b3@gregkh' --subject-prefix 'PATCH 6.12.y' HEAD^..

Here's one for 6.12-stable, just needed some trivial fixups.

-- 
Jens Axboe

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From b9c7da23ba07c6781e13f97398b2979d2ea6230f Mon Sep 17 00:00:00 2001
From: Jens Axboe <axboe@kernel.dk>
Date: Tue, 21 Oct 2025 07:16:08 -0600
Subject: [PATCH 1/2] io_uring/sqpoll: switch away from getrusage() for CPU
 accounting

Commit 8ac9b0d33e5c0a995338ee5f25fe1b6ff7d97f65 upstream.

getrusage() does a lot more than what the SQPOLL accounting needs, the
latter only cares about (and uses) the stime. Rather than do a full
RUSAGE_SELF summation, just query the used stime instead.

Cc: stable@vger.kernel.org
Fixes: 3fcb9d17206e ("io_uring/sqpoll: statistics of the true utilization of sq threads")
Reviewed-by: Gabriel Krisman Bertazi <krisman@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 io_uring/fdinfo.c |  8 ++++----
 io_uring/sqpoll.c | 32 ++++++++++++++++++--------------
 io_uring/sqpoll.h |  1 +
 3 files changed, 23 insertions(+), 18 deletions(-)

diff --git a/io_uring/fdinfo.c b/io_uring/fdinfo.c
index c6c624eb9866..5c0a02bfeb55 100644
--- a/io_uring/fdinfo.c
+++ b/io_uring/fdinfo.c
@@ -55,7 +55,6 @@ __cold void io_uring_show_fdinfo(struct seq_file *m, struct file *file)
 	struct io_ring_ctx *ctx = file->private_data;
 	struct io_overflow_cqe *ocqe;
 	struct io_rings *r = ctx->rings;
-	struct rusage sq_usage;
 	unsigned int sq_mask = ctx->sq_entries - 1, cq_mask = ctx->cq_entries - 1;
 	unsigned int sq_head = READ_ONCE(r->sq.head);
 	unsigned int sq_tail = READ_ONCE(r->sq.tail);
@@ -155,14 +154,15 @@ __cold void io_uring_show_fdinfo(struct seq_file *m, struct file *file)
 		 * thread termination.
 		 */
 		if (tsk) {
+			u64 usec;
+
 			get_task_struct(tsk);
 			rcu_read_unlock();
-			getrusage(tsk, RUSAGE_SELF, &sq_usage);
+			usec = io_sq_cpu_usec(tsk);
 			put_task_struct(tsk);
 			sq_pid = sq->task_pid;
 			sq_cpu = sq->sq_cpu;
-			sq_total_time = (sq_usage.ru_stime.tv_sec * 1000000
-					 + sq_usage.ru_stime.tv_usec);
+			sq_total_time = usec;
 			sq_work_time = sq->work_time;
 		} else {
 			rcu_read_unlock();
diff --git a/io_uring/sqpoll.c b/io_uring/sqpoll.c
index 2faa3058b2d0..af233b2fab10 100644
--- a/io_uring/sqpoll.c
+++ b/io_uring/sqpoll.c
@@ -11,6 +11,7 @@
 #include <linux/audit.h>
 #include <linux/security.h>
 #include <linux/cpuset.h>
+#include <linux/sched/cputime.h>
 #include <linux/io_uring.h>
 
 #include <uapi/linux/io_uring.h>
@@ -175,6 +176,20 @@ static inline bool io_sqd_events_pending(struct io_sq_data *sqd)
 	return READ_ONCE(sqd->state);
 }
 
+u64 io_sq_cpu_usec(struct task_struct *tsk)
+{
+	u64 utime, stime;
+
+	task_cputime_adjusted(tsk, &utime, &stime);
+	do_div(stime, 1000);
+	return stime;
+}
+
+static void io_sq_update_worktime(struct io_sq_data *sqd, u64 usec)
+{
+	sqd->work_time += io_sq_cpu_usec(current) - usec;
+}
+
 static int __io_sq_thread(struct io_ring_ctx *ctx, bool cap_entries)
 {
 	unsigned int to_submit;
@@ -261,26 +276,15 @@ static bool io_sq_tw_pending(struct llist_node *retry_list)
 	return retry_list || !llist_empty(&tctx->task_list);
 }
 
-static void io_sq_update_worktime(struct io_sq_data *sqd, struct rusage *start)
-{
-	struct rusage end;
-
-	getrusage(current, RUSAGE_SELF, &end);
-	end.ru_stime.tv_sec -= start->ru_stime.tv_sec;
-	end.ru_stime.tv_usec -= start->ru_stime.tv_usec;
-
-	sqd->work_time += end.ru_stime.tv_usec + end.ru_stime.tv_sec * 1000000;
-}
-
 static int io_sq_thread(void *data)
 {
 	struct llist_node *retry_list = NULL;
 	struct io_sq_data *sqd = data;
 	struct io_ring_ctx *ctx;
-	struct rusage start;
 	unsigned long timeout = 0;
 	char buf[TASK_COMM_LEN];
 	DEFINE_WAIT(wait);
+	u64 start;
 
 	/* offload context creation failed, just exit */
 	if (!current->io_uring) {
@@ -323,7 +327,7 @@ static int io_sq_thread(void *data)
 		}
 
 		cap_entries = !list_is_singular(&sqd->ctx_list);
-		getrusage(current, RUSAGE_SELF, &start);
+		start = io_sq_cpu_usec(current);
 		list_for_each_entry(ctx, &sqd->ctx_list, sqd_list) {
 			int ret = __io_sq_thread(ctx, cap_entries);
 
@@ -339,7 +343,7 @@ static int io_sq_thread(void *data)
 
 		if (sqt_spin || !time_after(jiffies, timeout)) {
 			if (sqt_spin) {
-				io_sq_update_worktime(sqd, &start);
+				io_sq_update_worktime(sqd, start);
 				timeout = jiffies + sqd->sq_thread_idle;
 			}
 			if (unlikely(need_resched())) {
diff --git a/io_uring/sqpoll.h b/io_uring/sqpoll.h
index b83dcdec9765..fd2f6f29b516 100644
--- a/io_uring/sqpoll.h
+++ b/io_uring/sqpoll.h
@@ -29,6 +29,7 @@ void io_sq_thread_unpark(struct io_sq_data *sqd);
 void io_put_sq_data(struct io_sq_data *sqd);
 void io_sqpoll_wait_sq(struct io_ring_ctx *ctx);
 int io_sqpoll_wq_cpu_affinity(struct io_ring_ctx *ctx, cpumask_var_t mask);
+u64 io_sq_cpu_usec(struct task_struct *tsk);
 
 static inline struct task_struct *sqpoll_task_locked(struct io_sq_data *sqd)
 {
-- 
2.51.0