Re: [RFC 0/7] io_uring lseek

Hao Xu
2023-07-27T12:30:58Z

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