On 05/27, Wenjie Qi wrote:
> F2FS iostat is optional and is disabled by default, but the direct
> I/O submit path still allocates and binds a bio_iostat_ctx, updates
> the submit timestamp, and replaces bi_end_io for every DIO bio even
> when sbi->iostat_enable is false.
>
> The end_io path also calls f2fs_update_iostat(), which returns
> immediately when iostat is disabled. This adds avoidable per-bio
> overhead to the default direct I/O hot path.
>
> Skip DIO iostat context setup and the direct read/write byte updates
> when iostat is disabled. If iostat is enabled through sysfs before
> submission, the existing context allocation and latency accounting path
> is still used.
>
> QEMU benchmark on a 1GiB F2FS virtio-blk image, with iostat_enable=0,
> 4KiB O_DIRECT I/O over a 64MiB file, 50000 iterations per run:
>
> baseline patched
> direct_read median 65264.50 ns 55470.95 ns
> direct_read recheck 65553.75 ns 55470.95 ns
> direct_write median 68054.62 ns 56309.44 ns
> direct_write recheck 66873.51 ns 56309.44 ns
>
> Signed-off-by: Wenjie Qi <[email protected]>
> ---
> fs/f2fs/file.c | 9 +++++++--
> fs/f2fs/iostat.h | 6 ++++++
> 2 files changed, 13 insertions(+), 2 deletions(-)
>
> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
> index 6edf0105dbc8..3ad8bd660b33 100644
> --- a/fs/f2fs/file.c
> +++ b/fs/f2fs/file.c
> @@ -4799,6 +4799,9 @@ static void f2fs_dio_iostat_start(struct f2fs_sb_info
> *sbi, struct bio *bio)
> {
> void *bi_private = bio->bi_private;
>
> + if (!f2fs_iostat_enabled(sbi))
> + return;
> +
> iostat_alloc_and_bind_ctx(sbi, bio, bi_private);
> iostat_update_submit_ctx(bio, DATA);
> bio->bi_end_io = f2fs_dio_end_bio;
> @@ -4816,7 +4819,8 @@ static int f2fs_dio_read_end_io(struct kiocb *iocb,
> ssize_t size, int error,
> dec_page_count(sbi, F2FS_DIO_READ);
> if (error)
> return error;
> - f2fs_update_iostat(sbi, NULL, APP_DIRECT_READ_IO, size);
> + if (f2fs_iostat_enabled(sbi))
> + f2fs_update_iostat(sbi, NULL, APP_DIRECT_READ_IO, size);
f2fs_update_iostat() checks sbi->iostat_enable?
> return 0;
> }
>
> @@ -5097,7 +5101,8 @@ static int f2fs_dio_write_end_io(struct kiocb *iocb,
> ssize_t size, int error,
> if (error)
> return error;
> f2fs_update_time(sbi, REQ_TIME);
> - f2fs_update_iostat(sbi, NULL, APP_DIRECT_IO, size);
> + if (f2fs_iostat_enabled(sbi))
> + f2fs_update_iostat(sbi, NULL, APP_DIRECT_IO, size);
> return 0;
> }
>
> diff --git a/fs/f2fs/iostat.h b/fs/f2fs/iostat.h
> index 2025225b5bed..d3ef787575be 100644
> --- a/fs/f2fs/iostat.h
> +++ b/fs/f2fs/iostat.h
> @@ -44,6 +44,11 @@ struct bio_iostat_ctx {
> struct bio_post_read_ctx *post_read_ctx;
> };
>
> +static inline bool f2fs_iostat_enabled(struct f2fs_sb_info *sbi)
> +{
> + return sbi->iostat_enable;
> +}
> +
> static inline void iostat_update_submit_ctx(struct bio *bio,
> enum page_type type)
> {
> @@ -72,6 +77,7 @@ static inline void f2fs_update_iostat(struct f2fs_sb_info
> *sbi, struct inode *in
> enum iostat_type type, unsigned long long io_bytes) {}
> static inline void f2fs_update_read_folio_count(struct f2fs_sb_info *sbi,
> struct folio *folio) {}
> +static inline bool f2fs_iostat_enabled(struct f2fs_sb_info *sbi) { return
> false; }
> static inline void iostat_update_and_unbind_ctx(struct bio *bio) {}
> static inline void iostat_alloc_and_bind_ctx(struct f2fs_sb_info *sbi,
> struct bio *bio, struct bio_post_read_ctx *ctx) {}
> --
> 2.43.0
>
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