Re: [RFC 0/7] io_uring lseek

[Hao Xu <hao.xu@linux.dev>]

On 7/26/23 18:25, Hao Xu wrote:
> From: Hao Xu <howeyxu@tencent.com>
> 
> This series adds lseek for io_uring, the motivation to import this
> syscall is in previous io_uring getdents patchset, we lack a way to
> rewind the file cursor when it goes to the end of file. Another reason
> is lseek is a common syscall, it's good for coding consistency when
> users use io_uring as their main loop.
> 
> Patch 1 is code clean for iomap
> Patch 2 adds IOMAP_NOWAIT logic for iomap lseek
> Patch 3 adds a nowait parameter to for IOMAP_NOWAIT control
> Patch 4 adds llseek_nowait() for file_operations so that specific
>          filesystem can implement it for nowait lseek
> Patch 5 adds llseek_nowait() implementation for xfs
> Patch 6 adds a new vfs wrapper for io_uring use
> Patch 7 is the main io_uring lseek implementation
> 
> Note, this series depends on the previous io_uring getdents series.
> 
> This is marked RFC since there is (at least) an issue to be discussed:
> The work in this series is mainly to reslove a problem that the current
> llseek() in struct file_operations doesn't have a place to deliver
> nowait info, and adding an argument to it results in update for llseek
> implementation of all filesystems (35 functions), so here I introduce
> a new llseek_nowait() as a workaround.
> 
> For performance, it has about 20%~30% improvement on iops.
> The test program is just like the one for io_uring getdents, here is the
> link to it: https://github.com/HowHsu/liburing/blob/llseek/test/lseek.c
> - Each test runs about 30000 async requests/sync syscalls
> - Each test runs 100 times and get the average value.
> - offset is randomly generated value
> - the file is a 1M all zero file
> 
> [howeyxu@~]$ python3 run_lseek.py
> test args:  seek mode:SEEK_SET, offset: 334772
> Average of  sync :  0.012300650000000002
> Average of  iouring :  0.008528009999999999
> 30.67%
> 
> [howeyxu@~]$ python3 run_lseek.py
> test args:  seek mode:SEEK_CUR, offset: 389292
> Average of  sync :  0.012736129999999995
> Average of  iouring :  0.00928725
> 27.08%
> 
> [howeyxu@~]$ python3 run_lseek.py
> test args:  seek mode:SEEK_END, offset: 281141
> Average of  sync :  0.01221595
> Average of  iouring :  0.008442890000000003
> 30.89%
> 
> [howeyxu@~]$ python3 run_lseek.py
> test args:  seek mode:SEEK_DATA, offset: 931103
> Average of  sync :  0.015496230000000005
> Average of  iouring :  0.012341509999999998
> 20.36%
> 
> [howeyxu@~]$ python3 run_lseek.py
> test args:  seek mode:SEEK_HOLE, offset: 430194
> Average of  sync :  0.01555663000000001
> Average of  iouring :  0.012064940000000003
> 22.45%
>   
> 
> Hao Xu (7):
>    iomap: merge iomap_seek_hole() and iomap_seek_data()
>    xfs: add nowait support for xfs_seek_iomap_begin()
>    add nowait parameter for iomap_seek()
>    add llseek_nowait() for struct file_operations
>    add llseek_nowait support for xfs
>    add vfs_lseek_nowait()
>    add lseek for io_uring
> 
>   fs/ext4/file.c                |  9 ++---
>   fs/gfs2/inode.c               |  4 +--
>   fs/iomap/seek.c               | 42 ++++++-----------------
>   fs/read_write.c               | 18 ++++++++++
>   fs/xfs/xfs_file.c             | 34 ++++++++++++++++---
>   fs/xfs/xfs_iomap.c            |  4 ++-
>   include/linux/fs.h            |  4 +++
>   include/linux/iomap.h         |  6 ++--
>   include/uapi/linux/io_uring.h |  1 +
>   io_uring/fs.c                 | 63 +++++++++++++++++++++++++++++++++++
>   io_uring/fs.h                 |  3 ++
>   io_uring/opdef.c              |  8 +++++
>   12 files changed, 145 insertions(+), 51 deletions(-)
> 
> 
> base-commit: 4a4b046082eca8ae90b654d772fccc30e9f23f4d

Hi folks,
I'll leave this patchset here before the io_uring getdents is merged,
then come back and update this one.

Thanks,
Hao