Sorry, this is only btrfs concerned, I made a typo in email address.
Thanks,
-liubo
On Tue, Feb 03, 2015 at 06:45:38PM +0800, Liu Bo wrote:
> Commit 1ae399382512 ("Btrfs: do not use async submit for small DIO io's")
> benefits small DIO io's.
>
> However, if we're owning the SINGLE profile, this also affects large DIO io's
> since in that case, map_length is (chunk_length - bio's offset_in_chunk),
> it's farily large so that it's very likely to be larger than a large bio's
> size, which avoids asynchronous submit.
> For instance, if we have a 512k bio, the efforts of calculating (512k/4k=128)
> checksums will be taken by the DIO task.
>
> Test results with fio (tested on a hard disk, not tested on ssd, 4cpu, 8g memory)
>
> bs async sync async sync
> bw bw(KB/S) iops iop
> 4k 115312 115480 28827.6 28869.6
> 8k 114381 115586 14297.4 14447.6
> 16k 115393 116290 7211.4 7267.6
> 32k 114268 116589 3570.4 3643
> 64k 115421 113417 1803 1771.8 <-----ASYNC wins here
> 128k 115545 112585 902 879
> 256k 115178 111521 449.2 435
> 512k 115874 111620 226 217.6
>
> This adds a limit 'BTRFS_STRIPE_LEN(64k)' to decide if it's small enough to avoid
> asynchronous submit.
>
> Still, in this case we don't need to split the bio and can submit it directly.
>
> Signed-off-by: Liu Bo <bo.li.liu@xxxxxxxxxx>
> ---
> The job in the test,
>
> [global]
> rw=write
> ioengine=libaio
> direct=1
> iodepth=64
> iodepth_batch=64
> iodepth_batch_complete=64
> iodepth_low=64
> bs=4k
> size=8g
> sync=0
> group_reporting
> fallocate=posix
> invalidate=1
> runtime=30
>
> [dio]
> directory=/mnt/btrfs
> filename=foobar
>
> fs/btrfs/inode.c | 16 ++++++++++++++--
> 1 file changed, 14 insertions(+), 2 deletions(-)
>
> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> index e687bb0..c640d7e 100644
> --- a/fs/btrfs/inode.c
> +++ b/fs/btrfs/inode.c
> @@ -7792,6 +7792,7 @@ static int btrfs_submit_direct_hook(int rw, struct btrfs_dio_private *dip,
> int nr_pages = 0;
> int ret;
> int async_submit = 0;
> + u64 alloc_profile;
>
> map_length = orig_bio->bi_iter.bi_size;
> ret = btrfs_map_block(root->fs_info, rw, start_sector << 9,
> @@ -7799,15 +7800,26 @@ static int btrfs_submit_direct_hook(int rw, struct btrfs_dio_private *dip,
> if (ret)
> return -EIO;
>
> + alloc_profile = btrfs_get_alloc_profile(root, 1);
> +
> if (map_length >= orig_bio->bi_iter.bi_size) {
> bio = orig_bio;
> dip->flags |= BTRFS_DIO_ORIG_BIO_SUBMITTED;
> +
> + /*
> + * In the case of 'single' profile, the above check is very
> + * likely to be true as map_length is (chunk_length - offset),
> + * so checking BTRFS_STRIPE_LEN here.
> + */
> + if ((alloc_profile & BTRFS_BLOCK_GROUP_PROFILE_MASK) == 0 &&
> + orig_bio->bi_iter.bi_size >= BTRFS_STRIPE_LEN)
> + async_submit = 1;
> +
> goto submit;
> }
>
> /* async crcs make it difficult to collect full stripe writes. */
> - if (btrfs_get_alloc_profile(root, 1) &
> - (BTRFS_BLOCK_GROUP_RAID5 | BTRFS_BLOCK_GROUP_RAID6))
> + if (alloc_profile & (BTRFS_BLOCK_GROUP_RAID5 | BTRFS_BLOCK_GROUP_RAID6))
> async_submit = 0;
> else
> async_submit = 1;
> --
> 1.8.1.4
>
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