Mailing List Archive

This patch is intended to release the CPU resources of io_uring in
polling mode. When IO is issued, the program immediately polls for
check completion, which is a waste of CPU resources when IO commands
are executed on the disk.

I add the hybrid polling feature in io_uring, enables polling to
release a portion of CPU resources without affecting block layer.

- Record the running time and context switching time of each
IO, and use these time to determine whether a process continue
to schedule.

- 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.

- Set a interface (ctx->flag) enables application to choose whether
or not to use this feature.

The CPU optimization in peak workload of patch is tested as follows:
all CPU utilization of original polling is 100% for per CPU, after
optimization, the CPU utilization drop a lot (per CPU);

read(128k, QD64, 1Job) 37% write(128k, QD64, 1Job) 40%
randread(4k, QD64, 16Job) 52% randwrite(4k, QD64, 16Job) 12%

Compared to original polling, the optimised performance reduction
with peak workload within 1%.

read 0.29% write 0.51% randread 0.09% randwrite 0%

Reviewed-by: KANCHAN JOSHI <joshi.k@samsung.com>
Signed-off-by: hexue <xue01.he@samsung.com>
---
include/linux/io_uring_types.h | 10 +++++
include/uapi/linux/io_uring.h | 1 +
io_uring/io_uring.c | 28 +++++++++++++-
io_uring/io_uring.h | 2 +
io_uring/rw.c | 69 ++++++++++++++++++++++++++++++++++
5 files changed, 109 insertions(+), 1 deletion(-)

diff --git a/include/linux/io_uring_types.h b/include/linux/io_uring_types.h
index 854ad67a5f70..7607fd8de91c 100644
--- a/include/linux/io_uring_types.h
+++ b/include/linux/io_uring_types.h
@@ -224,6 +224,11 @@ struct io_alloc_cache {
size_t elem_size;
};

+struct iopoll_info {
+ long last_runtime;
+ long last_irqtime;
+};
+
struct io_ring_ctx {
/* const or read-mostly hot data */
struct {
@@ -421,6 +426,7 @@ 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 +647,10 @@ struct io_kiocb {
u64 extra1;
u64 extra2;
} big_cqe;
+ /* for hybrid iopoll */
+ int poll_flag;
+ 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..0038cdfec18f 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_HY_POLL (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..bfb94e975f97 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"
@@ -311,6 +313,7 @@ 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);
@@ -1875,10 +1878,28 @@ static bool io_assign_file(struct io_kiocb *req, const struct io_issue_def *def,
return !!req->file;
}

+void init_hybrid_poll_info(struct io_ring_ctx *ctx, struct io_kiocb *req)
+{
+ u32 index;
+
+ 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->last_runtime = 0;
+ entry->last_irqtime = 0;
+ xa_store(&ctx->poll_array, index, entry, GFP_KERNEL);
+ }
+
+ ktime_get_ts64(&req->iopoll_start);
+}
+
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;

if (unlikely(!io_assign_file(req, def, issue_flags)))
@@ -1890,6 +1911,9 @@ 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_HY_POLL)
+ init_hybrid_poll_info(ctx, req);
+
ret = def->issue(req, issue_flags);

if (!def->audit_skip)
@@ -2176,6 +2200,7 @@ 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;

if (unlikely(opcode >= IORING_OP_LAST)) {
req->opcode = 0;
@@ -2921,6 +2946,7 @@ 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 +4076,7 @@ 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_HY_POLL))
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..d5b175826adb 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 1000
+
#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..ac73121030ee 100644
--- a/io_uring/rw.c
+++ b/io_uring/rw.c
@@ -1118,6 +1118,69 @@ 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)
+ return;
+
+ /*
+ * Avoid excessive scheduling time affecting performance
+ * by using only 25 per cent of the remaining time
+ */
+ sleep_ti = (entry->last_runtime - entry->last_irqtime) / 4;
+ if (sleep_ti < LEFT_TIME)
+ return;
+
+ ktime_get_ts64(&oldtc);
+ kt = ktime_set(0, sleep_ti);
+ req->poll_flag = 1;
+
+ 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 iouring_hybrid_poll(struct io_kiocb *req, struct io_comp_batch *iob, unsigned int poll_flags)
+{
+ struct io_rw *rw = io_kiocb_to_cmd(req, struct io_rw);
+ struct io_ring_ctx *ctx = req->ctx;
+ struct iopoll_info *entry;
+ int ret;
+ u32 index;
+
+ index = req->file->f_inode->i_rdev;
+ entry = xa_load(&ctx->poll_array, index);
+ io_delay(req, entry);
+ ret = req->file->f_op->iopoll(&rw->kiocb, iob, poll_flags);
+
+ ktime_get_ts64(&req->iopoll_end);
+ entry->last_runtime = req->iopoll_end.tv_nsec - req->iopoll_start.tv_nsec;
+ return ret;
+}
+
int io_do_iopoll(struct io_ring_ctx *ctx, bool force_nonspin)
{
struct io_wq_work_node *pos, *start, *prev;
@@ -1145,6 +1208,11 @@ int io_do_iopoll(struct io_ring_ctx *ctx, bool force_nonspin)
if (READ_ONCE(req->iopoll_completed))
break;

+ if (ctx->flags & IORING_SETUP_HY_POLL) {
+ ret = iouring_hybrid_poll(req, &iob, poll_flags);
+ goto comb;
+ }
+
if (req->opcode == IORING_OP_URING_CMD) {
struct io_uring_cmd *ioucmd;

@@ -1156,6 +1224,7 @@ int io_do_iopoll(struct io_ring_ctx *ctx, bool force_nonspin)

ret = file->f_op->iopoll(&rw->kiocb, &iob, poll_flags);
}
+comb:
if (unlikely(ret < 0))
return ret;
else if (ret)
--
2.40.1