support nonblock submission for splice pipe to pipe

RFC In review Hao Xu 4 participants 15 messages Jun 7, 2022 – Jun 14, 2022

Subsystems (3)

Memory management VFS io_uring

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Hao Xu

author

2022-06-07 08:06 UTC #0 lore raw

cover support nonblock submission for splice pipe to pipe

From: Hao Xu <[email protected]>

splice from pipe to pipe is a trivial case, and we can support nonblock try for it easily. splice depends on iowq at all which is slow. Let's build a fast submission path for it by supporting nonblock.

Wrote a simple test to test time spent of splicing from pipe to pipe:

Did 50 times test for each, ignore the highest and lowest number, calculate the average number:

before patchset: 119.85 usec
with patchset: 29.5 usec

----------------
I'm not sure if we should use a io_uring specific flag rather than SPLICE_F_NONBLOCK since from mutex_lock_nest to mutex_trylock changes the behavior under debug environment I guess. Or maybe there is another better option than mutex_trylock?

Hao Xu (5):
io_uring: move sp->len check up for splice and tee
pipe: add trylock helpers for pipe lock
splice: support nonblock for splice from pipe to pipe
io_uring: support nonblock try for splicing from pipe to pipe
io_uring: add file_in in io_splice{} to avoid duplicate calculation

 fs/pipe.c                 | 29 +++++++++++++++++++++
 fs/splice.c               | 21 +++++++++++++---
 include/linux/pipe_fs_i.h |  2 ++
 io_uring/splice.c         | 53 +++++++++++++++++++++++++++++----------
 4 files changed, 89 insertions(+), 16 deletions(-)

base-commit: d8271bf021438f468dab3cd84fe5279b5bbcead8

Signature · 1 line

2.25.1

Hao Xu

author

2022-06-07 08:06 UTC #1 lore raw

PATCH 1/5 io_uring: move sp->len check up for splice and tee

From: Hao Xu <[email protected]>

The traditional sync splice code return 0 if len is 0 at the beginning of syscall, similar thing for tee. So move up sp->len zero check so that it reaches quick ending when len is 0.

Signed-off-by Hao Xu <[email protected]>

---
 io_uring/splice.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

io_uring/splice.c +8 -4

index 0e19d6330345..b2cd1044c3ee 100644
@@ -53,6 +53,9 @@ int io_tee(struct io_kiocb *req, unsigned int issue_flags)
 	struct file *in;
 	long ret = 0;
 
+	if (unlikely(!sp->len))
+		goto done;
+
 	if (issue_flags & IO_URING_F_NONBLOCK)
 		return -EAGAIN;

@@ -65,8 +68,7 @@ int io_tee(struct io_kiocb *req, unsigned int issue_flags)
 		goto done;
 	}
 
-	if (sp->len)
-		ret = do_tee(in, out, sp->len, flags);
+	ret = do_tee(in, out, sp->len, flags);
 
 	if (!(sp->flags & SPLICE_F_FD_IN_FIXED))
 		io_put_file(in);

@@ -95,6 +97,9 @@ int io_splice(struct io_kiocb *req, unsigned int issue_flags)
 	struct file *in;
 	long ret = 0;
 
+	if (unlikely(!sp->len))
+		goto done;
+
 	if (issue_flags & IO_URING_F_NONBLOCK)
 		return -EAGAIN;

@@ -110,8 +115,7 @@ int io_splice(struct io_kiocb *req, unsigned int issue_flags)
 	poff_in = (sp->off_in == -1) ? NULL : &sp->off_in;
 	poff_out = (sp->off_out == -1) ? NULL : &sp->off_out;
 
-	if (sp->len)
-		ret = do_splice(in, poff_in, out, poff_out, sp->len, flags);
+	ret = do_splice(in, poff_in, out, poff_out, sp->len, flags);
 
 	if (!(sp->flags & SPLICE_F_FD_IN_FIXED))
 		io_put_file(in);

Signature · 1 line

2.25.1

Hao Xu

author

2022-06-07 08:06 UTC #2 lore raw

PATCH 2/5 pipe: add trylock helpers for pipe lock

In reply to Hao Xu

From: Hao Xu <[email protected]>

Add two helpers pipe_trylock() and pipe_double_trylock(), they are used in nonblock splice(pipe to pipe) scenario in next patches.

Signed-off-by Hao Xu <[email protected]>

---
 fs/pipe.c                 | 29 +++++++++++++++++++++++++++++
 include/linux/pipe_fs_i.h |  2 ++
 2 files changed, 31 insertions(+)

fs/pipe.c +29 -0

index 74ae9fafd25a..033736eb61fb 100644
@@ -98,6 +98,11 @@ void pipe_unlock(struct pipe_inode_info *pipe)
 }
 EXPORT_SYMBOL(pipe_unlock);
 
+int pipe_trylock(struct pipe_inode_info *pipe)
+{
+	return mutex_trylock(&pipe->mutex);
+}
+
 static inline void __pipe_lock(struct pipe_inode_info *pipe)
 {
 	mutex_lock_nested(&pipe->mutex, I_MUTEX_PARENT);

@@ -122,6 +127,30 @@ void pipe_double_lock(struct pipe_inode_info *pipe1,
 	}
 }
 
+int pipe_double_trylock(struct pipe_inode_info *pipe1,
+			 struct pipe_inode_info *pipe2)
+{
+	BUG_ON(pipe1 == pipe2);
+
+	if (pipe1 < pipe2) {
+		if (!pipe_trylock(pipe1))
+			return 0;
+		if (!pipe_trylock(pipe2)) {
+			pipe_unlock(pipe1);
+			return 0;
+		}
+	} else {
+		if (!pipe_trylock(pipe2))
+			return 0;
+		if (!pipe_trylock(pipe1)) {
+			pipe_unlock(pipe2);
+			return 0;
+		}
+	}
+
+	return 1;
+}
+
 static void anon_pipe_buf_release(struct pipe_inode_info *pipe,
 				  struct pipe_buffer *buf)
 {

include/linux/pipe_fs_i.h +2 -0

index cb0fd633a610..78dc2c7c999f 100644
@@ -235,8 +235,10 @@ static inline bool pipe_buf_try_steal(struct pipe_inode_info *pipe,
 
 /* Pipe lock and unlock operations */
 void pipe_lock(struct pipe_inode_info *);
+int pipe_trylock(struct pipe_inode_info *);
 void pipe_unlock(struct pipe_inode_info *);
 void pipe_double_lock(struct pipe_inode_info *, struct pipe_inode_info *);
+int pipe_double_trylock(struct pipe_inode_info *, struct pipe_inode_info *);
 
 /* Wait for a pipe to be readable/writable while dropping the pipe lock */
 void pipe_wait_readable(struct pipe_inode_info *);

Signature · 1 line

2.25.1

Hao Xu

author

2022-06-07 08:06 UTC #3 lore raw

PATCH 3/5 splice: support nonblock for splice from pipe to pipe

In reply to Hao Xu

From: Hao Xu <[email protected]>

When SPLICE_F_NONBLOCK is set, splice() still may be blocked by pipe lock in pipe to pipe scenario. Add trylock logic to make it more nonblock

Signed-off-by Hao Xu <[email protected]>

---
 fs/splice.c | 21 ++++++++++++++++++---
 1 file changed, 18 insertions(+), 3 deletions(-)

fs/splice.c +18 -3

index 047b79db8eb5..b087e00ed079 100644
@@ -1372,7 +1372,12 @@ static int ipipe_prep(struct pipe_inode_info *pipe, unsigned int flags)
 		return 0;
 
 	ret = 0;
-	pipe_lock(pipe);
+	if (flags & SPLICE_F_NONBLOCK) {
+		if (!pipe_trylock(pipe))
+			return -EAGAIN;
+	} else {
+		pipe_lock(pipe);
+	}
 
 	while (pipe_empty(pipe->head, pipe->tail)) {
 		if (signal_pending(current)) {

@@ -1408,7 +1413,12 @@ static int opipe_prep(struct pipe_inode_info *pipe, unsigned int flags)
 		return 0;
 
 	ret = 0;
-	pipe_lock(pipe);
+	if (flags & SPLICE_F_NONBLOCK) {
+		if (!pipe_trylock(pipe))
+			return -EAGAIN;
+	} else {
+		pipe_lock(pipe);
+	}
 
 	while (pipe_full(pipe->head, pipe->tail, pipe->max_usage)) {
 		if (!pipe->readers) {

@@ -1460,7 +1470,12 @@ static int splice_pipe_to_pipe(struct pipe_inode_info *ipipe,
 	 * grabbing by pipe info address. Otherwise two different processes
 	 * could deadlock (one doing tee from A -> B, the other from B -> A).
 	 */
-	pipe_double_lock(ipipe, opipe);
+	if (flags & SPLICE_F_NONBLOCK) {
+		if (!pipe_double_trylock(ipipe, opipe))
+			return -EAGAIN;
+	} else {
+		pipe_double_lock(ipipe, opipe);
+	}
 
 	i_tail = ipipe->tail;
 	i_mask = ipipe->ring_size - 1;

Signature · 1 line

2.25.1

Hao Xu

author

2022-06-07 08:07 UTC #4 lore raw

PATCH 4/5 io_uring: support nonblock try for splicing from pipe to pipe

In reply to Hao Xu

From: Hao Xu <[email protected]>

splice() in io_uring is running in a slow way since it fully depends on io workers. While splicing from pipe to pipe is a simpler case compared with file to pipe and pipe to file. Let's make it support nonblock first. This way we get a fast path for splicing fom pipe to pipe.

Signed-off-by Hao Xu <[email protected]>

---
 io_uring/splice.c | 24 +++++++++++++++++++++---
 1 file changed, 21 insertions(+), 3 deletions(-)

io_uring/splice.c +21 -3

index b2cd1044c3ee..650c70e3dde1 100644
@@ -88,6 +88,14 @@ int io_splice_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 	return __io_splice_prep(req, sqe);
 }
 
+bool io_splice_support_nowait(struct file *in, struct file *out)
+{
+	if (get_pipe_info(in, true) && get_pipe_info(out, true))
+		return true;
+
+	return false;
+}
+
 int io_splice(struct io_kiocb *req, unsigned int issue_flags)
 {
 	struct io_splice *sp = io_kiocb_to_cmd(req);

@@ -100,9 +108,6 @@ int io_splice(struct io_kiocb *req, unsigned int issue_flags)
 	if (unlikely(!sp->len))
 		goto done;
 
-	if (issue_flags & IO_URING_F_NONBLOCK)
-		return -EAGAIN;
-
 	if (sp->flags & SPLICE_F_FD_IN_FIXED)
 		in = io_file_get_fixed(req, sp->splice_fd_in, issue_flags);
 	else

@@ -112,6 +117,16 @@ int io_splice(struct io_kiocb *req, unsigned int issue_flags)
 		goto done;
 	}
 
+	if (issue_flags & IO_URING_F_NONBLOCK) {
+		if (io_splice_support_nowait(in, out)) {
+			flags |= SPLICE_F_NONBLOCK;
+		} else {
+			if (!(sp->flags & SPLICE_F_FD_IN_FIXED))
+				io_put_file(in);
+			return -EAGAIN;
+		}
+	}
+
 	poff_in = (sp->off_in == -1) ? NULL : &sp->off_in;
 	poff_out = (sp->off_out == -1) ? NULL : &sp->off_out;

@@ -119,6 +134,9 @@ int io_splice(struct io_kiocb *req, unsigned int issue_flags)
 
 	if (!(sp->flags & SPLICE_F_FD_IN_FIXED))
 		io_put_file(in);
+	if (ret == -EAGAIN)
+		return ret;
+
 done:
 	if (ret != sp->len)
 		req_set_fail(req);

Signature · 1 line

2.25.1

kernel test robot

build bot

2022-06-07 21:38 UTC #5 lore raw

Re: [PATCH 4/5] io_uring: support nonblock try for splicing from pipe to pipe

Thank you for the patch! Perhaps something to improve:

Hi Hao,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on d8271bf021438f468dab3cd84fe5279b5bbcead8]

url:    https://github.com/intel-lab-lkp/linux/commits/Hao-Xu/support-nonblock-submission-for-splice-pipe-to-pipe/20220607-161605
base:   d8271bf021438f468dab3cd84fe5279b5bbcead8
config: mips-buildonly-randconfig-r001-20220607 (https://download.01.org/0day-ci/archive/20220608/[email protected]/config)
compiler: clang version 15.0.0 (https://github.com/llvm/llvm-project b92436efcb7813fc481b30f2593a4907568d917a)

reproduce (this is a W=1 build):
wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross chmod +x ~/bin/make.cross
# install mips cross compiling tool for clang build
# apt-get install binutils-mips-linux-gnu
# https://github.com/intel-lab-lkp/linux/commit/96683840c3f19b77a536a259094d24e0cd93ebc0
git remote add linux-review https://github.com/intel-lab-lkp/linux
git fetch --no-tags linux-review Hao-Xu/support-nonblock-submission-for-splice-pipe-to-pipe/20220607-161605 git checkout 96683840c3f19b77a536a259094d24e0cd93ebc0
# save the config file
mkdir build_dir && cp config build_dir/.config
COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=mips SHELL=/bin/bash

If you fix the issue, kindly add following tag where applicable

Reported-by kernel test robot <[email protected]>

All warnings (new ones prefixed by >>):

>> io_uring/splice.c:91:6: warning: no previous prototype for function 'io_splice_support_nowait' [-Wmissing-prototypes]
   bool io_splice_support_nowait(struct file *in, struct file *out)
        ^

io_uring/splice.c:91:1: note: declare 'static' if the function is not intended to be used outside of this translation unit bool io_splice_support_nowait(struct file *in, struct file *out)
^
static
1 warning generated.

vim +/io_splice_support_nowait +91 io_uring/splice.c

    90	
  > 91	bool io_splice_support_nowait(struct file *in, struct file *out)
    92	{
    93		if (get_pipe_info(in, true) && get_pipe_info(out, true))
    94			return true;
    95	
    96		return false;
    97	}
    98

Signature · 2 lines

0-DAY CI Kernel Test Service
https://01.org/lkp

kernel test robot

build bot

2022-06-08 14:18 UTC #6 lore raw

Re: [PATCH 4/5] io_uring: support nonblock try for splicing from pipe to pipe

In reply to Hao Xu

Thank you for the patch! Perhaps something to improve:

Hi Hao,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on d8271bf021438f468dab3cd84fe5279b5bbcead8]

url:    https://github.com/intel-lab-lkp/linux/commits/Hao-Xu/support-nonblock-submission-for-splice-pipe-to-pipe/20220607-161605
base:   d8271bf021438f468dab3cd84fe5279b5bbcead8
config: x86_64-defconfig (https://download.01.org/0day-ci/archive/20220608/[email protected]/config)
compiler: gcc-11 (Debian 11.3.0-1) 11.3.0
reproduce (this is a W=1 build):
        # https://github.com/intel-lab-lkp/linux/commit/96683840c3f19b77a536a259094d24e0cd93ebc0
        git remote add linux-review https://github.com/intel-lab-lkp/linux
        git fetch --no-tags linux-review Hao-Xu/support-nonblock-submission-for-splice-pipe-to-pipe/20220607-161605
        git checkout 96683840c3f19b77a536a259094d24e0cd93ebc0
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        make W=1 O=build_dir ARCH=x86_64 SHELL=/bin/bash

If you fix the issue, kindly add following tag where applicable

Reported-by kernel test robot <[email protected]>

All warnings (new ones prefixed by >>):

>> io_uring/splice.c:91:6: warning: no previous prototype for 'io_splice_support_nowait' [-Wmissing-prototypes]

91 | bool io_splice_support_nowait(struct file *in, struct file *out)
| ^~~~~~~~~~~~~~~~~~~~~~~~

vim +/io_splice_support_nowait +91 io_uring/splice.c

    90	
  > 91	bool io_splice_support_nowait(struct file *in, struct file *out)
    92	{
    93		if (get_pipe_info(in, true) && get_pipe_info(out, true))
    94			return true;
    95	
    96		return false;
    97	}
    98

Signature · 2 lines

0-DAY CI Kernel Test Service
https://01.org/lkp

kernel test robot

build bot

2022-06-09 02:25 UTC #7 lore raw

Re: [PATCH 4/5] io_uring: support nonblock try for splicing from pipe to pipe

In reply to Hao Xu

Thank you for the patch! Perhaps something to improve:

Hi Hao,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on d8271bf021438f468dab3cd84fe5279b5bbcead8]

url:    https://github.com/intel-lab-lkp/linux/commits/Hao-Xu/support-nonblock-submission-for-splice-pipe-to-pipe/20220607-161605
base:   d8271bf021438f468dab3cd84fe5279b5bbcead8
config: i386-randconfig-s001 (https://download.01.org/0day-ci/archive/20220609/[email protected]/config)
compiler: gcc-11 (Debian 11.3.0-1) 11.3.0
reproduce:
        # apt-get install sparse
        # sparse version: v0.6.4-26-gb3cf30ba-dirty
        # https://github.com/intel-lab-lkp/linux/commit/96683840c3f19b77a536a259094d24e0cd93ebc0
        git remote add linux-review https://github.com/intel-lab-lkp/linux
        git fetch --no-tags linux-review Hao-Xu/support-nonblock-submission-for-splice-pipe-to-pipe/20220607-161605
        git checkout 96683840c3f19b77a536a259094d24e0cd93ebc0
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        make W=1 C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__' O=build_dir ARCH=i386 SHELL=/bin/bash

If you fix the issue, kindly add following tag where applicable

Reported-by kernel test robot <[email protected]>

sparse warnings: (new ones prefixed by >>)

>> io_uring/splice.c:91:6: sparse: sparse: symbol 'io_splice_support_nowait' was not declared. Should it be static?

Signature · 2 lines

0-DAY CI Kernel Test Service
https://01.org/lkp

Hao Xu

author

2022-06-07 08:07 UTC #8 lore raw

PATCH 5/5 io_uring: add file_in in io_splice{} to avoid duplicate calculation

In reply to Hao Xu

From: Hao Xu <[email protected]>

Add a member file_in in io_splice{} to avoid duplicate calculation of input file for splice. This is for the case where we do splice from pipe to pipe and get -EAGAIN for the inline submission.

Signed-off-by Hao Xu <[email protected]>

---
 io_uring/splice.c | 33 +++++++++++++++++++--------------
 1 file changed, 19 insertions(+), 14 deletions(-)

io_uring/splice.c +19 ~~-14~~

index 650c70e3dde1..c97f2971fe7e 100644
@@ -21,6 +21,7 @@ struct io_splice {
 	loff_t				off_in;
 	u64				len;
 	int				splice_fd_in;
+	struct file			*file_in;
 	unsigned int			flags;
 };

@@ -35,6 +36,7 @@ static int __io_splice_prep(struct io_kiocb *req,
 	if (unlikely(sp->flags & ~valid_flags))
 		return -EINVAL;
 	sp->splice_fd_in = READ_ONCE(sqe->splice_fd_in);
+	sp->file_in = NULL;
 	return 0;
 }

@@ -108,34 +110,37 @@ int io_splice(struct io_kiocb *req, unsigned int issue_flags)
 	if (unlikely(!sp->len))
 		goto done;
 
-	if (sp->flags & SPLICE_F_FD_IN_FIXED)
-		in = io_file_get_fixed(req, sp->splice_fd_in, issue_flags);
-	else
-		in = io_file_get_normal(req, sp->splice_fd_in);
-	if (!in) {
-		ret = -EBADF;
-		goto done;
+	if (!sp->file_in) {
+		if (sp->flags & SPLICE_F_FD_IN_FIXED)
+			in = io_file_get_fixed(req, sp->splice_fd_in, issue_flags);
+		else
+			in = io_file_get_normal(req, sp->splice_fd_in);
+
+		if (!in) {
+			ret = -EBADF;
+			goto done;
+		}
+		sp->file_in = in;
+	} else {
+		in = sp->file_in;
 	}
 
 	if (issue_flags & IO_URING_F_NONBLOCK) {
-		if (io_splice_support_nowait(in, out)) {
+		if (io_splice_support_nowait(in, out))
 			flags |= SPLICE_F_NONBLOCK;
-		} else {
-			if (!(sp->flags & SPLICE_F_FD_IN_FIXED))
-				io_put_file(in);
+		else
 			return -EAGAIN;
-		}
 	}
 
 	poff_in = (sp->off_in == -1) ? NULL : &sp->off_in;
 	poff_out = (sp->off_out == -1) ? NULL : &sp->off_out;
 
 	ret = do_splice(in, poff_in, out, poff_out, sp->len, flags);
+	if (ret == -EAGAIN)
+		return ret;
 
 	if (!(sp->flags & SPLICE_F_FD_IN_FIXED))
 		io_put_file(in);
-	if (ret == -EAGAIN)
-		return ret;
 
 done:
 	if (ret != sp->len)

Signature · 1 line

2.25.1

Hao Xu

author

2022-06-07 08:13 UTC #9 lore raw

In reply to Hao Xu

Hi,

Quoted 4 lines · Hao Xu

From: Hao Xu <[email protected]>
splice from pipe to pipe is a trivial case, and we can support nonblock try for it easily. splice depends on iowq at all which is slow. Let's

^ should be 'splice in io_uring'

Quoted 4 lines

build a fast submission path for it by supporting nonblock.
Wrote a simple test to test time spent of splicing from pipe to pipe:

Sorry, forgot to attach the test:
https://github.com/HowHsu/liburing/commit/3ff901b4fb80caf66a520742c6542e35111493a0

Regards,
Hao

Pavel Begunkov

2022-06-07 09:27 UTC #10 lore raw

In reply to Hao Xu

Quoted 5 lines · Hao Xu

From: Hao Xu <[email protected]>
splice from pipe to pipe is a trivial case, and we can support nonblock try for it easily. splice depends on iowq at all which is slow. Let's build a fast submission path for it by supporting nonblock.

fwiw,

https://www.spinics.net/lists/kernel/msg3652757.html

Quoted 31 lines

Wrote a simple test to test time spent of splicing from pipe to pipe:
Did 50 times test for each, ignore the highest and lowest number, calculate the average number:
before patchset: 119.85 usec
with patchset: 29.5 usec
----------------
I'm not sure if we should use a io_uring specific flag rather than SPLICE_F_NONBLOCK since from mutex_lock_nest to mutex_trylock changes the behavior under debug environment I guess. Or maybe there is another better option than mutex_trylock?
Hao Xu (5):
io_uring: move sp->len check up for splice and tee
pipe: add trylock helpers for pipe lock
splice: support nonblock for splice from pipe to pipe
io_uring: support nonblock try for splicing from pipe to pipe
io_uring: add file_in in io_splice{} to avoid duplicate calculation
  fs/pipe.c                 | 29 +++++++++++++++++++++
  fs/splice.c               | 21 +++++++++++++---
  include/linux/pipe_fs_i.h |  2 ++
  io_uring/splice.c         | 53 +++++++++++++++++++++++++++++----------
  4 files changed, 89 insertions(+), 16 deletions(-)
base-commit: d8271bf021438f468dab3cd84fe5279b5bbcead8

Signature · 1 line

Pavel Begunkov

Hao Xu

author

2022-06-08 06:43 UTC #11 lore raw

Quoted 11 lines · Pavel Begunkov

Quoted 5 lines · Hao Xu
From: Hao Xu <[email protected]>
splice from pipe to pipe is a trivial case, and we can support nonblock try for it easily. splice depends on iowq at all which is slow. Let's build a fast submission path for it by supporting nonblock.
fwiw,
https://www.spinics.net/lists/kernel/msg3652757.html

Thanks, Pavel. Seems it has been discussed for a long time but the
result remains unclear...For me, I think this patch is necessary for getting a good SPLICE_F_NONBLOCK user experience.

Jens Axboe

maintainer

2022-06-08 06:43 UTC #12 lore raw

Quoted 8 lines · Hao Xu

Quoted 7 lines · Pavel Begunkov
Quoted 5 lines · Hao Xu
From: Hao Xu <[email protected]>
splice from pipe to pipe is a trivial case, and we can support nonblock try for it easily. splice depends on iowq at all which is slow. Let's build a fast submission path for it by supporting nonblock.

Quoted 8 lines

Quoted 4 lines
fwiw,
https://www.spinics.net/lists/kernel/msg3652757.html
Thanks, Pavel. Seems it has been discussed for a long time but the result remains unclear...For me, I think this patch is necessary for getting a good SPLICE_F_NONBLOCK user experience.

I'd just take it up again, this is something we do need to get done to avoid io-wq offload. Which is important...

Signature · 1 line

Jens Axboe

Pavel Begunkov

2022-06-08 11:33 UTC #13 lore raw

In reply to Hao Xu

Quoted 8 lines · Hao Xu

Quoted 7 lines · Pavel Begunkov
Quoted 5 lines · Hao Xu
From: Hao Xu <[email protected]>
splice from pipe to pipe is a trivial case, and we can support nonblock try for it easily. splice depends on iowq at all which is slow. Let's build a fast submission path for it by supporting nonblock.

Quoted 7 lines

Quoted 4 lines
fwiw,
https://www.spinics.net/lists/kernel/msg3652757.html
Thanks, Pavel. Seems it has been discussed for a long time but the
result remains unclear...For me, I think this patch is necessary for getting a good SPLICE_F_NONBLOCK user experience.

I quite agree here, something like this is much needed. The performance of io_uring pipe I/O is miserably slow

Signature · 1 line

Pavel Begunkov

Hao Xu

author

2022-06-14 13:23 UTC #14 lore raw

In reply to Hao Xu

Quoted 6 lines · Hao Xu

From: Hao Xu <[email protected]>
splice from pipe to pipe is a trivial case, and we can support nonblock try for it easily. splice depends on iowq at all which is slow. Let's build a fast submission path for it by supporting nonblock.

Quoted 9 lines

Wrote a simple test to test time spent of splicing from pipe to pipe:
Did 50 times test for each, ignore the highest and lowest number, calculate the average number:
before patchset: 119.85 usec
with patchset: 29.5 usec

Hi Al,
Any comments on this one?

Regards,
Hao