* [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 related [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
[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 833 bytes --]
^ 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 related [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
end of thread, other threads:[~2020-02-12 12:57 UTC | newest]
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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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