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* [PATCH] fs: optimise kiocb_set_rw_flags()
@ 2020-01-17  1:16 Pavel Begunkov
  2020-01-17  1:21 ` Matthew Wilcox
  0 siblings, 1 reply; 6+ messages in thread
From: Pavel Begunkov @ 2020-01-17  1:16 UTC (permalink / raw)
  To: Alexander Viro, linux-fsdevel, linux-kernel

kiocb_set_rw_flags() generates a poor code with several memory writes
and a lot of jumps. Help compilers to optimise it.

Tested with gcc 9.2 on x64-86, and as a result, it its output now is a
plain code without jumps accumulating in a register before a memory
write.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
 include/linux/fs.h | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 98e0349adb52..c3db8c80aed4 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3402,22 +3402,27 @@ static inline int iocb_flags(struct file *file)
 
 static inline int kiocb_set_rw_flags(struct kiocb *ki, rwf_t flags)
 {
+	int kiocb_flags = 0;
+
 	if (unlikely(flags & ~RWF_SUPPORTED))
 		return -EOPNOTSUPP;
 
 	if (flags & RWF_NOWAIT) {
 		if (!(ki->ki_filp->f_mode & FMODE_NOWAIT))
 			return -EOPNOTSUPP;
-		ki->ki_flags |= IOCB_NOWAIT;
+		kiocb_flags |= IOCB_NOWAIT;
 	}
 	if (flags & RWF_HIPRI)
-		ki->ki_flags |= IOCB_HIPRI;
+		kiocb_flags |= IOCB_HIPRI;
 	if (flags & RWF_DSYNC)
-		ki->ki_flags |= IOCB_DSYNC;
+		kiocb_flags |= IOCB_DSYNC;
 	if (flags & RWF_SYNC)
-		ki->ki_flags |= (IOCB_DSYNC | IOCB_SYNC);
+		kiocb_flags |= (IOCB_DSYNC | IOCB_SYNC);
 	if (flags & RWF_APPEND)
-		ki->ki_flags |= IOCB_APPEND;
+		kiocb_flags |= IOCB_APPEND;
+
+	if (kiocb_flags)
+		ki->ki_flags |= kiocb_flags;
 	return 0;
 }
 
-- 
2.24.0


^ permalink raw reply	[flat|nested] 6+ messages in thread

* Re: [PATCH] fs: optimise kiocb_set_rw_flags()
  2020-01-17  1:16 [PATCH] fs: optimise kiocb_set_rw_flags() Pavel Begunkov
@ 2020-01-17  1:21 ` Matthew Wilcox
  2020-01-17  1:23   ` Pavel Begunkov
  0 siblings, 1 reply; 6+ messages in thread
From: Matthew Wilcox @ 2020-01-17  1:21 UTC (permalink / raw)
  To: Pavel Begunkov; +Cc: Alexander Viro, linux-fsdevel, linux-kernel

On Fri, Jan 17, 2020 at 04:16:41AM +0300, Pavel Begunkov wrote:
> kiocb_set_rw_flags() generates a poor code with several memory writes
> and a lot of jumps. Help compilers to optimise it.
> 
> Tested with gcc 9.2 on x64-86, and as a result, it its output now is a
> plain code without jumps accumulating in a register before a memory
> write.

Nice!

>  static inline int kiocb_set_rw_flags(struct kiocb *ki, rwf_t flags)
>  {
> +	int kiocb_flags = 0;
> +
>  	if (unlikely(flags & ~RWF_SUPPORTED))
>  		return -EOPNOTSUPP;
>  
>  	if (flags & RWF_NOWAIT) {
>  		if (!(ki->ki_filp->f_mode & FMODE_NOWAIT))
>  			return -EOPNOTSUPP;
> -		ki->ki_flags |= IOCB_NOWAIT;
> +		kiocb_flags |= IOCB_NOWAIT;
>  	}
>  	if (flags & RWF_HIPRI)
> -		ki->ki_flags |= IOCB_HIPRI;
> +		kiocb_flags |= IOCB_HIPRI;
>  	if (flags & RWF_DSYNC)
> -		ki->ki_flags |= IOCB_DSYNC;
> +		kiocb_flags |= IOCB_DSYNC;
>  	if (flags & RWF_SYNC)
> -		ki->ki_flags |= (IOCB_DSYNC | IOCB_SYNC);
> +		kiocb_flags |= (IOCB_DSYNC | IOCB_SYNC);
>  	if (flags & RWF_APPEND)
> -		ki->ki_flags |= IOCB_APPEND;
> +		kiocb_flags |= IOCB_APPEND;
> +
> +	if (kiocb_flags)
> +		ki->ki_flags |= kiocb_flags;
>  	return 0;
>  }

Might it generate even better code to do ...

 	int kiocb_flags = 0;
 
+	if (!flags)
+		return 0;
 	if (unlikely(flags & ~RWF_SUPPORTED))
 		return -EOPNOTSUPP;
 
...

-	if (kiocb_flags)
-		ki->ki_flags |= kiocb_flags;
+	ki->ki_flags |= kiocb_flags;

^ permalink raw reply	[flat|nested] 6+ messages in thread

* Re: [PATCH] fs: optimise kiocb_set_rw_flags()
  2020-01-17  1:21 ` Matthew Wilcox
@ 2020-01-17  1:23   ` Pavel Begunkov
  2020-01-17  1:32     ` [PATCH v2] " Pavel Begunkov
  0 siblings, 1 reply; 6+ messages in thread
From: Pavel Begunkov @ 2020-01-17  1:23 UTC (permalink / raw)
  To: Matthew Wilcox; +Cc: Alexander Viro, linux-fsdevel, linux-kernel

[-- Attachment #1.1: Type: text/plain, Size: 1669 bytes --]

On 17/01/2020 04:21, Matthew Wilcox wrote:
> On Fri, Jan 17, 2020 at 04:16:41AM +0300, Pavel Begunkov wrote:
>> kiocb_set_rw_flags() generates a poor code with several memory writes
>> and a lot of jumps. Help compilers to optimise it.
>>
>> Tested with gcc 9.2 on x64-86, and as a result, it its output now is a
>> plain code without jumps accumulating in a register before a memory
>> write.
> 
> Nice!
> 
>>  static inline int kiocb_set_rw_flags(struct kiocb *ki, rwf_t flags)
>>  {
>> +	int kiocb_flags = 0;
>> +
>>  	if (unlikely(flags & ~RWF_SUPPORTED))
>>  		return -EOPNOTSUPP;
>>  
>>  	if (flags & RWF_NOWAIT) {
>>  		if (!(ki->ki_filp->f_mode & FMODE_NOWAIT))
>>  			return -EOPNOTSUPP;
>> -		ki->ki_flags |= IOCB_NOWAIT;
>> +		kiocb_flags |= IOCB_NOWAIT;
>>  	}
>>  	if (flags & RWF_HIPRI)
>> -		ki->ki_flags |= IOCB_HIPRI;
>> +		kiocb_flags |= IOCB_HIPRI;
>>  	if (flags & RWF_DSYNC)
>> -		ki->ki_flags |= IOCB_DSYNC;
>> +		kiocb_flags |= IOCB_DSYNC;
>>  	if (flags & RWF_SYNC)
>> -		ki->ki_flags |= (IOCB_DSYNC | IOCB_SYNC);
>> +		kiocb_flags |= (IOCB_DSYNC | IOCB_SYNC);
>>  	if (flags & RWF_APPEND)
>> -		ki->ki_flags |= IOCB_APPEND;
>> +		kiocb_flags |= IOCB_APPEND;
>> +
>> +	if (kiocb_flags)
>> +		ki->ki_flags |= kiocb_flags;
>>  	return 0;
>>  }
> 
> Might it generate even better code to do ...

Good idea, thanks! I'll resend

> 
>  	int kiocb_flags = 0;
>  
> +	if (!flags)
> +		return 0;
>  	if (unlikely(flags & ~RWF_SUPPORTED))
>  		return -EOPNOTSUPP;
>  
> ...
> 
> -	if (kiocb_flags)
> -		ki->ki_flags |= kiocb_flags;
> +	ki->ki_flags |= kiocb_flags;
> 

-- 
Pavel Begunkov


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^ permalink raw reply	[flat|nested] 6+ messages in thread

* [PATCH v2] fs: optimise kiocb_set_rw_flags()
  2020-01-17  1:23   ` Pavel Begunkov
@ 2020-01-17  1:32     ` " Pavel Begunkov
  2020-01-31 13:01       ` Pavel Begunkov
  0 siblings, 1 reply; 6+ messages in thread
From: Pavel Begunkov @ 2020-01-17  1:32 UTC (permalink / raw)
  To: Alexander Viro, willy, linux-fsdevel, linux-kernel

kiocb_set_rw_flags() generates a poor code with several memory writes
and a lot of jumps. Help compilers to optimise it.

Tested with gcc 9.2 on x64-86, and as a result, it its output now is a
plain code without jumps accumulating in a register before a memory
write.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---

v2: check for 0 flags in advance (Matthew Wilcox)

 include/linux/fs.h | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 98e0349adb52..22b46fc8fdfa 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3402,22 +3402,28 @@ static inline int iocb_flags(struct file *file)
 
 static inline int kiocb_set_rw_flags(struct kiocb *ki, rwf_t flags)
 {
+	int kiocb_flags = 0;
+
+	if (!flags)
+		return 0;
 	if (unlikely(flags & ~RWF_SUPPORTED))
 		return -EOPNOTSUPP;
 
 	if (flags & RWF_NOWAIT) {
 		if (!(ki->ki_filp->f_mode & FMODE_NOWAIT))
 			return -EOPNOTSUPP;
-		ki->ki_flags |= IOCB_NOWAIT;
+		kiocb_flags |= IOCB_NOWAIT;
 	}
 	if (flags & RWF_HIPRI)
-		ki->ki_flags |= IOCB_HIPRI;
+		kiocb_flags |= IOCB_HIPRI;
 	if (flags & RWF_DSYNC)
-		ki->ki_flags |= IOCB_DSYNC;
+		kiocb_flags |= IOCB_DSYNC;
 	if (flags & RWF_SYNC)
-		ki->ki_flags |= (IOCB_DSYNC | IOCB_SYNC);
+		kiocb_flags |= (IOCB_DSYNC | IOCB_SYNC);
 	if (flags & RWF_APPEND)
-		ki->ki_flags |= IOCB_APPEND;
+		kiocb_flags |= IOCB_APPEND;
+
+	ki->ki_flags |= kiocb_flags;
 	return 0;
 }
 
-- 
2.24.0


^ permalink raw reply	[flat|nested] 6+ messages in thread

* Re: [PATCH v2] fs: optimise kiocb_set_rw_flags()
  2020-01-17  1:32     ` [PATCH v2] " Pavel Begunkov
@ 2020-01-31 13:01       ` Pavel Begunkov
  2020-02-12 12:57         ` Pavel Begunkov
  0 siblings, 1 reply; 6+ messages in thread
From: Pavel Begunkov @ 2020-01-31 13:01 UTC (permalink / raw)
  To: Alexander Viro, willy, linux-fsdevel, linux-kernel

On 1/17/2020 4:32 AM, Pavel Begunkov wrote:
> kiocb_set_rw_flags() generates a poor code with several memory writes
> and a lot of jumps. Help compilers to optimise it.
> 
> Tested with gcc 9.2 on x64-86, and as a result, it its output now is a
> plain code without jumps accumulating in a register before a memory
> write.

Humble ping

> 
> Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
> ---
> 
> v2: check for 0 flags in advance (Matthew Wilcox)
> 
>  include/linux/fs.h | 16 +++++++++++-----
>  1 file changed, 11 insertions(+), 5 deletions(-)
> 
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 98e0349adb52..22b46fc8fdfa 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -3402,22 +3402,28 @@ static inline int iocb_flags(struct file *file)
>  
>  static inline int kiocb_set_rw_flags(struct kiocb *ki, rwf_t flags)
>  {
> +	int kiocb_flags = 0;
> +
> +	if (!flags)
> +		return 0;
>  	if (unlikely(flags & ~RWF_SUPPORTED))
>  		return -EOPNOTSUPP;
>  
>  	if (flags & RWF_NOWAIT) {
>  		if (!(ki->ki_filp->f_mode & FMODE_NOWAIT))
>  			return -EOPNOTSUPP;
> -		ki->ki_flags |= IOCB_NOWAIT;
> +		kiocb_flags |= IOCB_NOWAIT;
>  	}
>  	if (flags & RWF_HIPRI)
> -		ki->ki_flags |= IOCB_HIPRI;
> +		kiocb_flags |= IOCB_HIPRI;
>  	if (flags & RWF_DSYNC)
> -		ki->ki_flags |= IOCB_DSYNC;
> +		kiocb_flags |= IOCB_DSYNC;
>  	if (flags & RWF_SYNC)
> -		ki->ki_flags |= (IOCB_DSYNC | IOCB_SYNC);
> +		kiocb_flags |= (IOCB_DSYNC | IOCB_SYNC);
>  	if (flags & RWF_APPEND)
> -		ki->ki_flags |= IOCB_APPEND;
> +		kiocb_flags |= IOCB_APPEND;
> +
> +	ki->ki_flags |= kiocb_flags;
>  	return 0;
>  }
>  
> 

-- 
Pavel Begunkov

^ permalink raw reply	[flat|nested] 6+ messages in thread

* Re: [PATCH v2] fs: optimise kiocb_set_rw_flags()
  2020-01-31 13:01       ` Pavel Begunkov
@ 2020-02-12 12:57         ` Pavel Begunkov
  0 siblings, 0 replies; 6+ messages in thread
From: Pavel Begunkov @ 2020-02-12 12:57 UTC (permalink / raw)
  To: Alexander Viro, willy, linux-fsdevel, linux-kernel

On 1/31/2020 4:01 PM, Pavel Begunkov wrote:
> On 1/17/2020 4:32 AM, Pavel Begunkov wrote:
>> kiocb_set_rw_flags() generates a poor code with several memory writes
>> and a lot of jumps. Help compilers to optimise it.
>>
>> Tested with gcc 9.2 on x64-86, and as a result, it its output now is a
>> plain code without jumps accumulating in a register before a memory
>> write.
> 
> Humble ping

Anyone?

> 
>>
>> Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
>> ---
>>
>> v2: check for 0 flags in advance (Matthew Wilcox)
>>
>>  include/linux/fs.h | 16 +++++++++++-----
>>  1 file changed, 11 insertions(+), 5 deletions(-)
>>
>> diff --git a/include/linux/fs.h b/include/linux/fs.h
>> index 98e0349adb52..22b46fc8fdfa 100644
>> --- a/include/linux/fs.h
>> +++ b/include/linux/fs.h
>> @@ -3402,22 +3402,28 @@ static inline int iocb_flags(struct file *file)
>>  
>>  static inline int kiocb_set_rw_flags(struct kiocb *ki, rwf_t flags)
>>  {
>> +	int kiocb_flags = 0;
>> +
>> +	if (!flags)
>> +		return 0;
>>  	if (unlikely(flags & ~RWF_SUPPORTED))
>>  		return -EOPNOTSUPP;
>>  
>>  	if (flags & RWF_NOWAIT) {
>>  		if (!(ki->ki_filp->f_mode & FMODE_NOWAIT))
>>  			return -EOPNOTSUPP;
>> -		ki->ki_flags |= IOCB_NOWAIT;
>> +		kiocb_flags |= IOCB_NOWAIT;
>>  	}
>>  	if (flags & RWF_HIPRI)
>> -		ki->ki_flags |= IOCB_HIPRI;
>> +		kiocb_flags |= IOCB_HIPRI;
>>  	if (flags & RWF_DSYNC)
>> -		ki->ki_flags |= IOCB_DSYNC;
>> +		kiocb_flags |= IOCB_DSYNC;
>>  	if (flags & RWF_SYNC)
>> -		ki->ki_flags |= (IOCB_DSYNC | IOCB_SYNC);
>> +		kiocb_flags |= (IOCB_DSYNC | IOCB_SYNC);
>>  	if (flags & RWF_APPEND)
>> -		ki->ki_flags |= IOCB_APPEND;
>> +		kiocb_flags |= IOCB_APPEND;
>> +
>> +	ki->ki_flags |= kiocb_flags;
>>  	return 0;
>>  }
>>  
>>
> 

-- 
Pavel Begunkov

^ permalink raw reply	[flat|nested] 6+ messages in thread

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Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-01-17  1:16 [PATCH] fs: optimise kiocb_set_rw_flags() Pavel Begunkov
2020-01-17  1:21 ` Matthew Wilcox
2020-01-17  1:23   ` Pavel Begunkov
2020-01-17  1:32     ` [PATCH v2] " Pavel Begunkov
2020-01-31 13:01       ` Pavel Begunkov
2020-02-12 12:57         ` Pavel Begunkov

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