* FAILED: patch "[PATCH] io_uring/sqpoll: be smarter on when to update the stime usage" failed to apply to 6.12-stable tree
@ 2025-10-26 14:22 gregkh
2025-10-26 14:28 ` Jens Axboe
0 siblings, 1 reply; 3+ messages in thread
From: gregkh @ 2025-10-26 14:22 UTC (permalink / raw)
To: axboe, changfengnan; +Cc: stable
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 a94e0657269c5b8e1a90b17aa2c048b3d276e16d
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2025102618-plastic-eldercare-f957@gregkh' --subject-prefix 'PATCH 6.12.y' HEAD^..
Possible dependencies:
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From a94e0657269c5b8e1a90b17aa2c048b3d276e16d Mon Sep 17 00:00:00 2001
From: Jens Axboe <axboe@kernel.dk>
Date: Tue, 21 Oct 2025 11:44:39 -0600
Subject: [PATCH] io_uring/sqpoll: be smarter on when to update the stime usage
The current approach is a bit naive, and hence calls the time querying
way too often. Only start the "doing work" timer when there's actual
work to do, and then use that information to terminate (and account) the
work time once done. This greatly reduces the frequency of these calls,
when they cannot have changed anyway.
Running a basic random reader that is setup to use SQPOLL, a profile
before this change shows these as the top cycle consumers:
+ 32.60% iou-sqp-1074 [kernel.kallsyms] [k] thread_group_cputime_adjusted
+ 19.97% iou-sqp-1074 [kernel.kallsyms] [k] thread_group_cputime
+ 12.20% io_uring io_uring [.] submitter_uring_fn
+ 4.13% iou-sqp-1074 [kernel.kallsyms] [k] getrusage
+ 2.45% iou-sqp-1074 [kernel.kallsyms] [k] io_submit_sqes
+ 2.18% iou-sqp-1074 [kernel.kallsyms] [k] __pi_memset_generic
+ 2.09% iou-sqp-1074 [kernel.kallsyms] [k] cputime_adjust
and after this change, top of profile looks as follows:
+ 36.23% io_uring io_uring [.] submitter_uring_fn
+ 23.26% iou-sqp-819 [kernel.kallsyms] [k] io_sq_thread
+ 10.14% iou-sqp-819 [kernel.kallsyms] [k] io_sq_tw
+ 6.52% iou-sqp-819 [kernel.kallsyms] [k] tctx_task_work_run
+ 4.82% iou-sqp-819 [kernel.kallsyms] [k] nvme_submit_cmds.part.0
+ 2.91% iou-sqp-819 [kernel.kallsyms] [k] io_submit_sqes
[...]
0.02% iou-sqp-819 [kernel.kallsyms] [k] cputime_adjust
where it's spending the cycles on things that actually matter.
Reported-by: Fengnan Chang <changfengnan@bytedance.com>
Cc: stable@vger.kernel.org
Fixes: 3fcb9d17206e ("io_uring/sqpoll: statistics of the true utilization of sq threads")
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/io_uring/sqpoll.c b/io_uring/sqpoll.c
index 2b816fdb9866..e22f072c7d5f 100644
--- a/io_uring/sqpoll.c
+++ b/io_uring/sqpoll.c
@@ -170,6 +170,11 @@ static inline bool io_sqd_events_pending(struct io_sq_data *sqd)
return READ_ONCE(sqd->state);
}
+struct io_sq_time {
+ bool started;
+ u64 usec;
+};
+
u64 io_sq_cpu_usec(struct task_struct *tsk)
{
u64 utime, stime;
@@ -179,12 +184,24 @@ u64 io_sq_cpu_usec(struct task_struct *tsk)
return stime;
}
-static void io_sq_update_worktime(struct io_sq_data *sqd, u64 usec)
+static void io_sq_update_worktime(struct io_sq_data *sqd, struct io_sq_time *ist)
{
- sqd->work_time += io_sq_cpu_usec(current) - usec;
+ if (!ist->started)
+ return;
+ ist->started = false;
+ sqd->work_time += io_sq_cpu_usec(current) - ist->usec;
}
-static int __io_sq_thread(struct io_ring_ctx *ctx, bool cap_entries)
+static void io_sq_start_worktime(struct io_sq_time *ist)
+{
+ if (ist->started)
+ return;
+ ist->started = true;
+ ist->usec = io_sq_cpu_usec(current);
+}
+
+static int __io_sq_thread(struct io_ring_ctx *ctx, struct io_sq_data *sqd,
+ bool cap_entries, struct io_sq_time *ist)
{
unsigned int to_submit;
int ret = 0;
@@ -197,6 +214,8 @@ static int __io_sq_thread(struct io_ring_ctx *ctx, bool cap_entries)
if (to_submit || !wq_list_empty(&ctx->iopoll_list)) {
const struct cred *creds = NULL;
+ io_sq_start_worktime(ist);
+
if (ctx->sq_creds != current_cred())
creds = override_creds(ctx->sq_creds);
@@ -278,7 +297,6 @@ static int io_sq_thread(void *data)
unsigned long timeout = 0;
char buf[TASK_COMM_LEN] = {};
DEFINE_WAIT(wait);
- u64 start;
/* offload context creation failed, just exit */
if (!current->io_uring) {
@@ -313,6 +331,7 @@ static int io_sq_thread(void *data)
mutex_lock(&sqd->lock);
while (1) {
bool cap_entries, sqt_spin = false;
+ struct io_sq_time ist = { };
if (io_sqd_events_pending(sqd) || signal_pending(current)) {
if (io_sqd_handle_event(sqd))
@@ -321,9 +340,8 @@ static int io_sq_thread(void *data)
}
cap_entries = !list_is_singular(&sqd->ctx_list);
- start = io_sq_cpu_usec(current);
list_for_each_entry(ctx, &sqd->ctx_list, sqd_list) {
- int ret = __io_sq_thread(ctx, cap_entries);
+ int ret = __io_sq_thread(ctx, sqd, cap_entries, &ist);
if (!sqt_spin && (ret > 0 || !wq_list_empty(&ctx->iopoll_list)))
sqt_spin = true;
@@ -331,15 +349,18 @@ static int io_sq_thread(void *data)
if (io_sq_tw(&retry_list, IORING_TW_CAP_ENTRIES_VALUE))
sqt_spin = true;
- list_for_each_entry(ctx, &sqd->ctx_list, sqd_list)
- if (io_napi(ctx))
+ list_for_each_entry(ctx, &sqd->ctx_list, sqd_list) {
+ if (io_napi(ctx)) {
+ io_sq_start_worktime(&ist);
io_napi_sqpoll_busy_poll(ctx);
+ }
+ }
+
+ io_sq_update_worktime(sqd, &ist);
if (sqt_spin || !time_after(jiffies, timeout)) {
- if (sqt_spin) {
- io_sq_update_worktime(sqd, start);
+ if (sqt_spin)
timeout = jiffies + sqd->sq_thread_idle;
- }
if (unlikely(need_resched())) {
mutex_unlock(&sqd->lock);
cond_resched();
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: FAILED: patch "[PATCH] io_uring/sqpoll: be smarter on when to update the stime usage" failed to apply to 6.12-stable tree
2025-10-26 14:22 FAILED: patch "[PATCH] io_uring/sqpoll: be smarter on when to update the stime usage" failed to apply to 6.12-stable tree gregkh
@ 2025-10-26 14:28 ` Jens Axboe
2025-10-26 14:56 ` Greg KH
0 siblings, 1 reply; 3+ messages in thread
From: Jens Axboe @ 2025-10-26 14:28 UTC (permalink / raw)
To: gregkh, changfengnan; +Cc: stable
[-- Attachment #1: Type: text/plain, Size: 856 bytes --]
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 a94e0657269c5b8e1a90b17aa2c048b3d276e16d
> # <resolve conflicts, build, test, etc.>
> git commit -s
> git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2025102618-plastic-eldercare-f957@gregkh' --subject-prefix 'PATCH 6.12.y' HEAD^..
And here's this one, just a single fuzzed commit after patch 1 got
applied.
--
Jens Axboe
[-- Attachment #2: 0002-io_uring-sqpoll-be-smarter-on-when-to-update-the-sti.patch --]
[-- Type: text/x-patch, Size: 5228 bytes --]
From bfe554574c418c0ef57cd234bed1bf31e9bb4f00 Mon Sep 17 00:00:00 2001
From: Jens Axboe <axboe@kernel.dk>
Date: Tue, 21 Oct 2025 11:44:39 -0600
Subject: [PATCH 2/2] io_uring/sqpoll: be smarter on when to update the stime
usage
Commit a94e0657269c5b8e1a90b17aa2c048b3d276e16d upstream.
The current approach is a bit naive, and hence calls the time querying
way too often. Only start the "doing work" timer when there's actual
work to do, and then use that information to terminate (and account) the
work time once done. This greatly reduces the frequency of these calls,
when they cannot have changed anyway.
Running a basic random reader that is setup to use SQPOLL, a profile
before this change shows these as the top cycle consumers:
+ 32.60% iou-sqp-1074 [kernel.kallsyms] [k] thread_group_cputime_adjusted
+ 19.97% iou-sqp-1074 [kernel.kallsyms] [k] thread_group_cputime
+ 12.20% io_uring io_uring [.] submitter_uring_fn
+ 4.13% iou-sqp-1074 [kernel.kallsyms] [k] getrusage
+ 2.45% iou-sqp-1074 [kernel.kallsyms] [k] io_submit_sqes
+ 2.18% iou-sqp-1074 [kernel.kallsyms] [k] __pi_memset_generic
+ 2.09% iou-sqp-1074 [kernel.kallsyms] [k] cputime_adjust
and after this change, top of profile looks as follows:
+ 36.23% io_uring io_uring [.] submitter_uring_fn
+ 23.26% iou-sqp-819 [kernel.kallsyms] [k] io_sq_thread
+ 10.14% iou-sqp-819 [kernel.kallsyms] [k] io_sq_tw
+ 6.52% iou-sqp-819 [kernel.kallsyms] [k] tctx_task_work_run
+ 4.82% iou-sqp-819 [kernel.kallsyms] [k] nvme_submit_cmds.part.0
+ 2.91% iou-sqp-819 [kernel.kallsyms] [k] io_submit_sqes
[...]
0.02% iou-sqp-819 [kernel.kallsyms] [k] cputime_adjust
where it's spending the cycles on things that actually matter.
Reported-by: Fengnan Chang <changfengnan@bytedance.com>
Cc: stable@vger.kernel.org
Fixes: 3fcb9d17206e ("io_uring/sqpoll: statistics of the true utilization of sq threads")
Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
io_uring/sqpoll.c | 43 ++++++++++++++++++++++++++++++++-----------
1 file changed, 32 insertions(+), 11 deletions(-)
diff --git a/io_uring/sqpoll.c b/io_uring/sqpoll.c
index af233b2fab10..44e7959b52d9 100644
--- a/io_uring/sqpoll.c
+++ b/io_uring/sqpoll.c
@@ -176,6 +176,11 @@ static inline bool io_sqd_events_pending(struct io_sq_data *sqd)
return READ_ONCE(sqd->state);
}
+struct io_sq_time {
+ bool started;
+ u64 usec;
+};
+
u64 io_sq_cpu_usec(struct task_struct *tsk)
{
u64 utime, stime;
@@ -185,12 +190,24 @@ u64 io_sq_cpu_usec(struct task_struct *tsk)
return stime;
}
-static void io_sq_update_worktime(struct io_sq_data *sqd, u64 usec)
+static void io_sq_update_worktime(struct io_sq_data *sqd, struct io_sq_time *ist)
+{
+ if (!ist->started)
+ return;
+ ist->started = false;
+ sqd->work_time += io_sq_cpu_usec(current) - ist->usec;
+}
+
+static void io_sq_start_worktime(struct io_sq_time *ist)
{
- sqd->work_time += io_sq_cpu_usec(current) - usec;
+ if (ist->started)
+ return;
+ ist->started = true;
+ ist->usec = io_sq_cpu_usec(current);
}
-static int __io_sq_thread(struct io_ring_ctx *ctx, bool cap_entries)
+static int __io_sq_thread(struct io_ring_ctx *ctx, struct io_sq_data *sqd,
+ bool cap_entries, struct io_sq_time *ist)
{
unsigned int to_submit;
int ret = 0;
@@ -203,6 +220,8 @@ static int __io_sq_thread(struct io_ring_ctx *ctx, bool cap_entries)
if (to_submit || !wq_list_empty(&ctx->iopoll_list)) {
const struct cred *creds = NULL;
+ io_sq_start_worktime(ist);
+
if (ctx->sq_creds != current_cred())
creds = override_creds(ctx->sq_creds);
@@ -284,7 +303,6 @@ static int io_sq_thread(void *data)
unsigned long timeout = 0;
char buf[TASK_COMM_LEN];
DEFINE_WAIT(wait);
- u64 start;
/* offload context creation failed, just exit */
if (!current->io_uring) {
@@ -319,6 +337,7 @@ static int io_sq_thread(void *data)
mutex_lock(&sqd->lock);
while (1) {
bool cap_entries, sqt_spin = false;
+ struct io_sq_time ist = { };
if (io_sqd_events_pending(sqd) || signal_pending(current)) {
if (io_sqd_handle_event(sqd))
@@ -327,9 +346,8 @@ static int io_sq_thread(void *data)
}
cap_entries = !list_is_singular(&sqd->ctx_list);
- start = io_sq_cpu_usec(current);
list_for_each_entry(ctx, &sqd->ctx_list, sqd_list) {
- int ret = __io_sq_thread(ctx, cap_entries);
+ int ret = __io_sq_thread(ctx, sqd, cap_entries, &ist);
if (!sqt_spin && (ret > 0 || !wq_list_empty(&ctx->iopoll_list)))
sqt_spin = true;
@@ -337,15 +355,18 @@ static int io_sq_thread(void *data)
if (io_sq_tw(&retry_list, IORING_TW_CAP_ENTRIES_VALUE))
sqt_spin = true;
- list_for_each_entry(ctx, &sqd->ctx_list, sqd_list)
- if (io_napi(ctx))
+ list_for_each_entry(ctx, &sqd->ctx_list, sqd_list) {
+ if (io_napi(ctx)) {
+ io_sq_start_worktime(&ist);
io_napi_sqpoll_busy_poll(ctx);
+ }
+ }
+
+ io_sq_update_worktime(sqd, &ist);
if (sqt_spin || !time_after(jiffies, timeout)) {
- if (sqt_spin) {
- io_sq_update_worktime(sqd, start);
+ if (sqt_spin)
timeout = jiffies + sqd->sq_thread_idle;
- }
if (unlikely(need_resched())) {
mutex_unlock(&sqd->lock);
cond_resched();
--
2.51.0
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: FAILED: patch "[PATCH] io_uring/sqpoll: be smarter on when to update the stime usage" failed to apply to 6.12-stable tree
2025-10-26 14:28 ` Jens Axboe
@ 2025-10-26 14:56 ` Greg KH
0 siblings, 0 replies; 3+ messages in thread
From: Greg KH @ 2025-10-26 14:56 UTC (permalink / raw)
To: Jens Axboe; +Cc: changfengnan, stable
On Sun, Oct 26, 2025 at 08:28:07AM -0600, Jens Axboe wrote:
> 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 a94e0657269c5b8e1a90b17aa2c048b3d276e16d
> > # <resolve conflicts, build, test, etc.>
> > git commit -s
> > git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2025102618-plastic-eldercare-f957@gregkh' --subject-prefix 'PATCH 6.12.y' HEAD^..
>
> And here's this one, just a single fuzzed commit after patch 1 got
> applied.
Both now queued up, thanks.
greg k-h
^ permalink raw reply [flat|nested] 3+ messages in thread
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2025-10-26 14:22 FAILED: patch "[PATCH] io_uring/sqpoll: be smarter on when to update the stime usage" failed to apply to 6.12-stable tree gregkh
2025-10-26 14:28 ` Jens Axboe
2025-10-26 14:56 ` Greg KH
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