[PATCH] io_uring: releasing CPU resources when polling

From: Xue
Date: Mon Mar 18 2024 - 05:00:53 EST

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From: hexue <xue01.he@xxxxxxxxxxx>

This patch is intended to reduce the CPU usage of io_uring in polling
mode. When io_uring is configured to use polling but the
underlying device is not configured with poll queue, this patch is
trying to optimaize the CPU when io_uring is polling for completions
of IOs that will actually be completed via interrupts.

The patch is implemented as follows:
- Get the poll queue information of the underling device
in io_uring.

- If there is no poll queue, IO will be arrive as
interruption, then io_uring's polling detection will keep
spinning empty, resulting in a waste of CPU resources,
so let the process release CPU before IO completes.

- Record the running time and context switching time of each
IO, and use these time to determine whether a process continue
to schedule.
In specific implementations, applying to consecutive IOs, each
IO is judged based on the recording time of the previous IO,
and when the idle time is greater than 1us, it will schedule to
ensure that the performance is not compromised.

- Adaptive adjustment to different devices. Due to the real-time
nature of time recording, each device's IO processing speed is
different, so the CPU optimization effect will vary, but could
ensure that the performance will not be degraded.

- Set a interface enables application to choose whether or not
to require this feature.
Add a tag of flag, when the application adds this tag, the
optimization provided by this patch will only be adopted if
the above condition is met, i.e., if io_uring is polling and
the underlying device is not configured with a poll queue,
which means that the user chooses the CPU low-loss prioritized
approach for IO. If the application does not set this tag, then
even if the conditions are met, it will remain the same as
native io_uring, with no changes or impacts.

The CPU optimization of patch is tested as follows:
In the case of reaching the peak of the disk's spec, the
performance is not significantly reduced from native kernel,
but the CPU usage of per CPU is reduced by about 50% for
sequential R&W, and by ~80% for Randomwrite.

This optimization does not affect IO performance in other cases,
e.g., when both the underlying device and io_uring allow
polling, performance is not affected by this patch.

- test tool: Fio 3.35, 8 core VM
- test method: Run performance tests on bare disks
and use the htop tool to observe CPU utilization
- Fio peak workload command:
[global]
ioengine=io_uring
norandommap=1
randrepeat=0
refill_buffers
group_reporting
ramp_time=30s
time_based
runtime=1m
filename=/dev/nvme0n1
hipri=1
direct=1
iodepth=64

[disk0] | [disk0]
bs=4k | bs=128k
numjobs=16 | numjobs=1
rw=randread/randwrite | rw=read/write

- Detailed test results
|-------------|---------|--------------------|
| rw=read | BW/s |per CPU utilization |
| Native | 10.9G | 100% |
|Optimization | 10.8G | 44% |

|-------------|---------|--------------------|
| rw=write | BW/s |per CPU utilization |
| Native | 6175 | 100% |
|Optimization | 6150 | 32% |

|-------------|---------|--------------------|
| rw=randread | KIOPS |per CPU utilization |
| Native | 1680 | 100% |
|Optimization | 1608 | 100% |

|-------------|---------|--------------------|
| rw=randwrite| KIOPS |per CPU utilization |
| Native | 225 | 100% |
|Optimization | 225 | 15% |

Signed-off-by: hexue <xue01.he@xxxxxxxxxxx>
---
include/linux/io_uring_types.h | 12 ++++++++
include/uapi/linux/io_uring.h | 1 +
io_uring/io_uring.c | 47 ++++++++++++++++++++++++++++-
io_uring/io_uring.h | 2 ++
io_uring/rw.c | 55 ++++++++++++++++++++++++++++++++++
5 files changed, 116 insertions(+), 1 deletion(-)

diff --git a/include/linux/io_uring_types.h b/include/linux/io_uring_types.h
index 854ad67a5f70..55d22f6e1eb0 100644
--- a/include/linux/io_uring_types.h
+++ b/include/linux/io_uring_types.h
@@ -224,6 +224,12 @@ struct io_alloc_cache {
size_t elem_size;
};

+struct iopoll_info {
+ bool poll_state;
+ long last_runtime;
+ long last_irqtime;
+};
+
struct io_ring_ctx {
/* const or read-mostly hot data */
struct {
@@ -421,6 +427,7 @@ struct io_ring_ctx {
unsigned short n_sqe_pages;
struct page **ring_pages;
struct page **sqe_pages;
+ struct xarray poll_array;
};

struct io_tw_state {
@@ -641,6 +648,11 @@ struct io_kiocb {
u64 extra1;
u64 extra2;
} big_cqe;
+ /* for adaptive iopoll */
+ int poll_flag;
+ bool poll_state;
+ struct timespec64 iopoll_start;
+ struct timespec64 iopoll_end;
};

struct io_overflow_cqe {
diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index 7a673b52827b..cd11a7786c51 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -198,6 +198,7 @@ enum {
* Removes indirection through the SQ index array.
*/
#define IORING_SETUP_NO_SQARRAY (1U << 16)
+#define IORING_SETUP_NO_POLLQUEUE (1U << 17)

enum io_uring_op {
IORING_OP_NOP,
diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index cd9a137ad6ce..9609acc60868 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -79,6 +79,8 @@

#include <uapi/linux/io_uring.h>

+#include <linux/time.h>
+#include <linux/timekeeping.h>
#include "io-wq.h"

#include "io_uring.h"
@@ -122,6 +124,9 @@
#define IO_COMPL_BATCH 32
#define IO_REQ_ALLOC_BATCH 8

+#define IO_POLL_QUEUE 1
+#define IO_NO_POLL_QUEUE 0
+
enum {
IO_CHECK_CQ_OVERFLOW_BIT,
IO_CHECK_CQ_DROPPED_BIT,
@@ -311,6 +316,7 @@ static __cold struct io_ring_ctx *io_ring_ctx_alloc(struct io_uring_params *p)
goto err;

ctx->flags = p->flags;
+ xa_init(&ctx->poll_array);
atomic_set(&ctx->cq_wait_nr, IO_CQ_WAKE_INIT);
init_waitqueue_head(&ctx->sqo_sq_wait);
INIT_LIST_HEAD(&ctx->sqd_list);
@@ -1875,11 +1881,32 @@ static bool io_assign_file(struct io_kiocb *req, const struct io_issue_def *def,
return !!req->file;
}

+/* Get poll queue information of the device */
+int get_poll_queue_state(struct io_kiocb *req)
+{
+ struct block_device *bdev;
+ struct request_queue *q;
+ struct inode *inode;
+
+ inode = req->file->f_inode;
+ if (!inode->i_rdev)
+ return 1;
+ bdev = blkdev_get_no_open(inode->i_rdev);
+ q = bdev->bd_queue;
+ if (!test_bit(QUEUE_FLAG_POLL, &q->queue_flags)) {
+ return IO_NO_POLL_QUEUE;
+ } else {
+ return IO_POLL_QUEUE;
+ }
+}
+
static int io_issue_sqe(struct io_kiocb *req, unsigned int issue_flags)
{
const struct io_issue_def *def = &io_issue_defs[req->opcode];
const struct cred *creds = NULL;
+ struct io_ring_ctx *ctx = req->ctx;
int ret;
+ u32 index;

if (unlikely(!io_assign_file(req, def, issue_flags)))
return -EBADF;
@@ -1890,6 +1917,21 @@ static int io_issue_sqe(struct io_kiocb *req, unsigned int issue_flags)
if (!def->audit_skip)
audit_uring_entry(req->opcode);

+ if (ctx->flags & IORING_SETUP_NO_POLLQUEUE) {
+ index = req->file->f_inode->i_rdev;
+ struct iopoll_info *entry = xa_load(&ctx->poll_array, index);
+
+ if (!entry) {
+ entry = kmalloc(sizeof(struct iopoll_info), GFP_KERNEL);
+ entry->poll_state = get_poll_queue_state(req);
+ entry->last_runtime = 0;
+ entry->last_irqtime = 0;
+ xa_store(&ctx->poll_array, index, entry, GFP_KERNEL);
+ }
+ req->poll_state = entry->poll_state;
+ ktime_get_ts64(&req->iopoll_start);
+ }
+
ret = def->issue(req, issue_flags);

if (!def->audit_skip)
@@ -2176,6 +2218,8 @@ static int io_init_req(struct io_ring_ctx *ctx, struct io_kiocb *req,
req->file = NULL;
req->rsrc_node = NULL;
req->task = current;
+ req->poll_flag = 0;
+ req->poll_state = 1;

if (unlikely(opcode >= IORING_OP_LAST)) {
req->opcode = 0;
@@ -2921,6 +2965,7 @@ static __cold void io_ring_ctx_free(struct io_ring_ctx *ctx)
kfree(ctx->cancel_table_locked.hbs);
kfree(ctx->io_bl);
xa_destroy(&ctx->io_bl_xa);
+ xa_destroy(&ctx->poll_array);
kfree(ctx);
}

@@ -4050,7 +4095,7 @@ static long io_uring_setup(u32 entries, struct io_uring_params __user *params)
IORING_SETUP_SQE128 | IORING_SETUP_CQE32 |
IORING_SETUP_SINGLE_ISSUER | IORING_SETUP_DEFER_TASKRUN |
IORING_SETUP_NO_MMAP | IORING_SETUP_REGISTERED_FD_ONLY |
- IORING_SETUP_NO_SQARRAY))
+ IORING_SETUP_NO_SQARRAY | IORING_SETUP_NO_POLLQUEUE))
return -EINVAL;

return io_uring_create(entries, &p, params);
diff --git a/io_uring/io_uring.h b/io_uring/io_uring.h
index d5495710c178..4281a0bb7ed9 100644
--- a/io_uring/io_uring.h
+++ b/io_uring/io_uring.h
@@ -125,6 +125,8 @@ static inline void io_req_task_work_add(struct io_kiocb *req)
__io_req_task_work_add(req, 0);
}

+#define LEFT_TIME 3000
+
#define io_for_each_link(pos, head) \
for (pos = (head); pos; pos = pos->link)

diff --git a/io_uring/rw.c b/io_uring/rw.c
index d5e79d9bdc71..db589a2cf659 100644
--- a/io_uring/rw.c
+++ b/io_uring/rw.c
@@ -1118,6 +1118,44 @@ void io_rw_fail(struct io_kiocb *req)
io_req_set_res(req, res, req->cqe.flags);
}

+void io_delay(struct io_kiocb *req, struct iopoll_info *entry)
+{
+ struct hrtimer_sleeper timer;
+ ktime_t kt;
+ struct timespec64 tc, oldtc;
+ enum hrtimer_mode mode;
+ long sleep_ti;
+
+ if (req->poll_flag == 1)
+ return;
+
+ if (entry->last_runtime <= entry->last_irqtime || (entry->last_runtime - entry->last_irqtime) < LEFT_TIME)
+ return;
+
+ req->poll_flag = 1;
+ ktime_get_ts64(&oldtc);
+ sleep_ti = (entry->last_runtime - entry->last_irqtime) / 2;
+ kt = ktime_set(0, sleep_ti);
+
+ mode = HRTIMER_MODE_REL;
+ hrtimer_init_sleeper_on_stack(&timer, CLOCK_MONOTONIC, mode);
+ hrtimer_set_expires(&timer.timer, kt);
+
+ set_current_state(TASK_UNINTERRUPTIBLE);
+ hrtimer_sleeper_start_expires(&timer, mode);
+ if (timer.task) {
+ io_schedule();
+ }
+ hrtimer_cancel(&timer.timer);
+ mode = HRTIMER_MODE_ABS;
+
+ __set_current_state(TASK_RUNNING);
+ destroy_hrtimer_on_stack(&timer.timer);
+
+ ktime_get_ts64(&tc);
+ entry->last_irqtime = tc.tv_nsec - oldtc.tv_nsec - sleep_ti;
+}
+
int io_do_iopoll(struct io_ring_ctx *ctx, bool force_nonspin)
{
struct io_wq_work_node *pos, *start, *prev;
@@ -1136,12 +1174,28 @@ int io_do_iopoll(struct io_ring_ctx *ctx, bool force_nonspin)
struct io_kiocb *req = container_of(pos, struct io_kiocb, comp_list);
struct file *file = req->file;
int ret;
+ u32 index = file->f_inode->i_rdev;

/*
* Move completed and retryable entries to our local lists.
* If we find a request that requires polling, break out
* and complete those lists first, if we have entries there.
*/
+
+ if ((ctx->flags & IORING_SETUP_NO_POLLQUEUE) && !req->poll_state) {
+ struct iopoll_info *entry = xa_load(&ctx->poll_array, index);
+
+ do {
+ if (READ_ONCE(req->iopoll_completed)) {
+ ktime_get_ts64(&req->iopoll_end);
+ entry->last_runtime = req->iopoll_end.tv_nsec - req->iopoll_start.tv_nsec;
+ break;
+ }
+ io_delay(req, entry);
+ } while (1);
+ goto complete;
+ }
+
if (READ_ONCE(req->iopoll_completed))
break;

@@ -1172,6 +1226,7 @@ int io_do_iopoll(struct io_ring_ctx *ctx, bool force_nonspin)
else if (!pos)
return 0;

+complete:
prev = start;
wq_list_for_each_resume(pos, prev) {
struct io_kiocb *req = container_of(pos, struct io_kiocb, comp_list);
--
2.34.1

Next message: Nam Cao: "Re: Boot hang with SiFive PLIC when routing I2C-HID level-triggered interrupts"
Previous message: Li Feng: "Re: [PATCH v2 2/2] nvme/tcp: Add wq_unbound modparam for nvme_tcp_wq"
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