Generally applications have 1 or a few waits of waiting, yet they pass
in a struct io_uring_getevents_arg every time. This needs to get copied
and, in turn, the timeout value needs to get copied.
Rather than do this for every invocation, allow the application to
register a fixed set of wait regions that can simply be indexed when
asking the kernel to wait on events.
At ring setup time, the application can register a number of these wait
regions ala:
struct io_uring_reg_wait *reg;
posix_memalign((void **) ®, page_size, page_size);
memset(reg, 0, page_size);
/* set timeout and mark it as set, sigmask/sigmask_sz as needed */
reg->ts.tv_sec = 0;
reg->ts.tv_nsec = 100000;
reg->flags = IORING_REG_WAIT_TS;
io_uring_register_cqwait_reg(ring, reg, nr_regions);
and instead of doing:
struct __kernel_timespec timeout = { .tv_nsec = 100000, };
io_uring_submit_and_wait_timeout(ring, &cqe, nr, &t, NULL);
for each submit_and_wait, or just wait, operation, it can just reference
the above region at offset 0 and do:
io_uring_submit_and_wait_reg(ring, &cqe, nr, 0);
to achieve the same goal of waiting 100usec without needing to copy
both struct io_uring_getevents_arg (24b) and struct __kernel_timeout
(16b) for each invocation. Struct io_uring_reg_wait looks as follows:
struct io_uring_reg_wait {
struct __kernel_timespec ts;
__u32 min_wait_usec;
__u32 flags;
__u64 sigmask;
__u32 sigmask_sz;
__u32 pad[3];
__u64 pad2[2];
};
embedding the timeout itself in the region, rather than passing it as
a pointer as well. Note that the signal mask is still passed as a
pointer, both for compatability reasons, but also because there doesn't
seem to be a lot of high frequency waits scenarios that involve setting
and resetting the signal mask for each wait.
The application is free to modify any region before a wait call, or it
can use keep multiple regions with different settings to avoid needing to
modify the same one for wait calls. Up to a page size of regions is mapped
by default, allowing PAGE_SIZE / 64 available regions for use.
In network performance testing with zero-copy, this reduced the time
spent waiting on the TX side from 3.12% to 0.3% and the RX side from 4.4%
to 0.3%.
Wait regions are fixed for the lifetime of the ring - once registered,
they are persistent until the ring is torn down.
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
---
include/linux/io_uring_types.h | 7 ++++
include/uapi/linux/io_uring.h | 18 +++++++++
io_uring/io_uring.c | 72 ++++++++++++++++++++++++++++------
io_uring/register.c | 48 +++++++++++++++++++++++
4 files changed, 134 insertions(+), 11 deletions(-)
diff --git a/include/linux/io_uring_types.h b/include/linux/io_uring_types.h
index 6d3ee71bd832..40dc1ec37a42 100644
--- a/include/linux/io_uring_types.h
+++ b/include/linux/io_uring_types.h
@@ -327,6 +327,13 @@ struct io_ring_ctx {
atomic_t cq_wait_nr;
atomic_t cq_timeouts;
struct wait_queue_head cq_wait;
+
+ /*
+ * If registered with IORING_REGISTER_CQWAIT_REG, a single
+ * page holds N entries, mapped in cq_wait_arg.
+ */
+ struct page **cq_wait_page;
+ struct io_uring_reg_wait *cq_wait_arg;
} ____cacheline_aligned_in_smp;
/* timeouts */
diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index c4737892c7cd..4ead32fa9275 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -518,6 +518,7 @@ struct io_cqring_offsets {
#define IORING_ENTER_EXT_ARG (1U << 3)
#define IORING_ENTER_REGISTERED_RING (1U << 4)
#define IORING_ENTER_ABS_TIMER (1U << 5)
+#define IORING_ENTER_EXT_ARG_REG (1U << 6)
/*
* Passed in for io_uring_setup(2). Copied back with updated info on success
@@ -618,6 +619,9 @@ enum io_uring_register_op {
/* resize CQ ring */
IORING_REGISTER_RESIZE_RINGS = 33,
+ /* register fixed io_uring_reg_wait arguments */
+ IORING_REGISTER_CQWAIT_REG = 34,
+
/* this goes last */
IORING_REGISTER_LAST,
@@ -801,6 +805,20 @@ enum io_uring_register_restriction_op {
IORING_RESTRICTION_LAST
};
+enum {
+ IORING_REG_WAIT_TS = (1U << 0),
+};
+
+struct io_uring_reg_wait {
+ struct __kernel_timespec ts;
+ __u32 min_wait_usec;
+ __u32 flags;
+ __u64 sigmask;
+ __u32 sigmask_sz;
+ __u32 pad[3];
+ __u64 pad2[2];
+};
+
struct io_uring_getevents_arg {
__u64 sigmask;
__u32 sigmask_sz;
diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index 612e7d66f845..0b76b4becda9 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -2735,6 +2735,10 @@ static __cold void io_ring_ctx_free(struct io_ring_ctx *ctx)
io_alloc_cache_free(&ctx->msg_cache, io_msg_cache_free);
io_futex_cache_free(ctx);
io_destroy_buffers(ctx);
+ if (ctx->cq_wait_page) {
+ unsigned short npages = 1;
+ io_pages_unmap(ctx->cq_wait_arg, &ctx->cq_wait_page, &npages, true);
+ }
mutex_unlock(&ctx->uring_lock);
if (ctx->sq_creds)
put_cred(ctx->sq_creds);
@@ -3223,21 +3227,44 @@ void __io_uring_cancel(bool cancel_all)
io_uring_cancel_generic(cancel_all, NULL);
}
-static int io_validate_ext_arg(unsigned flags, const void __user *argp, size_t argsz)
+static struct io_uring_reg_wait *io_get_ext_arg_fixed(struct io_ring_ctx *ctx,
+ const struct io_uring_getevents_arg __user *uarg)
+{
+ struct io_uring_reg_wait *arg = READ_ONCE(ctx->cq_wait_arg);
+
+ if (arg) {
+ unsigned int index = (unsigned int) (uintptr_t) uarg;
+
+ if (index >= PAGE_SIZE / sizeof(struct io_uring_reg_wait))
+ return ERR_PTR(-EINVAL);
+ return arg + index;
+ }
+
+ return ERR_PTR(-EFAULT);
+}
+
+static int io_validate_ext_arg(struct io_ring_ctx *ctx, unsigned flags,
+ const void __user *argp, size_t argsz)
{
- if (flags & IORING_ENTER_EXT_ARG) {
- struct io_uring_getevents_arg arg;
+ struct io_uring_getevents_arg arg;
- if (argsz != sizeof(arg))
+ if (!(flags & IORING_ENTER_EXT_ARG))
+ return 0;
+
+ if (flags & IORING_ENTER_EXT_ARG_REG) {
+ if (argsz != sizeof(struct io_uring_reg_wait))
return -EINVAL;
- if (copy_from_user(&arg, argp, sizeof(arg)))
- return -EFAULT;
+ return PTR_ERR(io_get_ext_arg_fixed(ctx, argp));
}
+ if (argsz != sizeof(arg))
+ return -EINVAL;
+ if (copy_from_user(&arg, argp, sizeof(arg)))
+ return -EFAULT;
return 0;
}
-static int io_get_ext_arg(unsigned flags, const void __user *argp,
- struct ext_arg *ext_arg)
+static int io_get_ext_arg(struct io_ring_ctx *ctx, unsigned flags,
+ const void __user *argp, struct ext_arg *ext_arg)
{
const struct io_uring_getevents_arg __user *uarg = argp;
struct io_uring_getevents_arg arg;
@@ -3251,6 +3278,28 @@ static int io_get_ext_arg(unsigned flags, const void __user *argp,
return 0;
}
+ if (flags & IORING_ENTER_EXT_ARG_REG) {
+ struct io_uring_reg_wait *w;
+
+ if (ext_arg->argsz != sizeof(struct io_uring_reg_wait))
+ return -EINVAL;
+ w = io_get_ext_arg_fixed(ctx, argp);
+ if (IS_ERR(w))
+ return PTR_ERR(w);
+
+ if (w->flags & ~IORING_REG_WAIT_TS)
+ return -EINVAL;
+ ext_arg->min_time = READ_ONCE(w->min_wait_usec) * NSEC_PER_USEC;
+ ext_arg->sig = u64_to_user_ptr(READ_ONCE(w->sigmask));
+ ext_arg->argsz = READ_ONCE(w->sigmask_sz);
+ if (w->flags & IORING_REG_WAIT_TS) {
+ ext_arg->ts.tv_sec = READ_ONCE(w->ts.tv_sec);
+ ext_arg->ts.tv_nsec = READ_ONCE(w->ts.tv_nsec);
+ ext_arg->ts_set = true;
+ }
+ return 0;
+ }
+
/*
* EXT_ARG is set - ensure we agree on the size of it and copy in our
* timespec and sigset_t pointers if good.
@@ -3289,7 +3338,8 @@ SYSCALL_DEFINE6(io_uring_enter, unsigned int, fd, u32, to_submit,
if (unlikely(flags & ~(IORING_ENTER_GETEVENTS | IORING_ENTER_SQ_WAKEUP |
IORING_ENTER_SQ_WAIT | IORING_ENTER_EXT_ARG |
IORING_ENTER_REGISTERED_RING |
- IORING_ENTER_ABS_TIMER)))
+ IORING_ENTER_ABS_TIMER |
+ IORING_ENTER_EXT_ARG_REG)))
return -EINVAL;
/*
@@ -3372,7 +3422,7 @@ SYSCALL_DEFINE6(io_uring_enter, unsigned int, fd, u32, to_submit,
*/
mutex_lock(&ctx->uring_lock);
iopoll_locked:
- ret2 = io_validate_ext_arg(flags, argp, argsz);
+ ret2 = io_validate_ext_arg(ctx, flags, argp, argsz);
if (likely(!ret2)) {
min_complete = min(min_complete,
ctx->cq_entries);
@@ -3382,7 +3432,7 @@ SYSCALL_DEFINE6(io_uring_enter, unsigned int, fd, u32, to_submit,
} else {
struct ext_arg ext_arg = { .argsz = argsz };
- ret2 = io_get_ext_arg(flags, argp, &ext_arg);
+ ret2 = io_get_ext_arg(ctx, flags, argp, &ext_arg);
if (likely(!ret2)) {
min_complete = min(min_complete,
ctx->cq_entries);
diff --git a/io_uring/register.c b/io_uring/register.c
index 8fbce6f268b6..edf6c218b228 100644
--- a/io_uring/register.c
+++ b/io_uring/register.c
@@ -520,6 +520,48 @@ static int io_register_resize_rings(struct io_ring_ctx *ctx, void __user *arg)
return 0;
}
+/*
+ * Register a page holding N entries of struct io_uring_reg_wait, which can
+ * be used via io_uring_enter(2) if IORING_GETEVENTS_EXT_ARG_REG is set.
+ * If that is set with IORING_GETEVENTS_EXT_ARG, then instead of passing
+ * in a pointer for a struct io_uring_getevents_arg, an index into this
+ * registered array is passed, avoiding two (arg + timeout) copies per
+ * invocation.
+ */
+static int io_register_cqwait_reg(struct io_ring_ctx *ctx, void __user *uarg,
+ unsigned nr_args)
+{
+ struct io_uring_reg_wait *arg;
+ struct page **pages;
+ unsigned long len;
+ int nr_pages;
+
+ if (ctx->cq_wait_page || ctx->cq_wait_arg)
+ return -EBUSY;
+ if (check_mul_overflow(sizeof(*arg), nr_args, &len))
+ return -EOVERFLOW;
+ if (len > PAGE_SIZE)
+ return -EINVAL;
+
+ pages = io_pin_pages((unsigned long) uarg, len, &nr_pages);
+ if (IS_ERR(pages))
+ return PTR_ERR(pages);
+ if (nr_pages != 1) {
+ io_pages_free(&pages, nr_pages);
+ return -EINVAL;
+ }
+
+ arg = vmap(pages, 1, VM_MAP, PAGE_KERNEL);
+ if (arg) {
+ WRITE_ONCE(ctx->cq_wait_page, pages);
+ WRITE_ONCE(ctx->cq_wait_arg, arg);
+ return 0;
+ }
+
+ io_pages_free(&pages, 1);
+ return -ENOMEM;
+}
+
static int __io_uring_register(struct io_ring_ctx *ctx, unsigned opcode,
void __user *arg, unsigned nr_args)
__releases(ctx->uring_lock)
@@ -714,6 +756,12 @@ static int __io_uring_register(struct io_ring_ctx *ctx, unsigned opcode,
break;
ret = io_register_resize_rings(ctx, arg);
break;
+ case IORING_REGISTER_CQWAIT_REG:
+ ret = -EINVAL;
+ if (!arg)
+ break;
+ ret = io_register_cqwait_reg(ctx, arg, nr_args);
+ break;
default:
ret = -EINVAL;
break;
--
2.45.2
