Re: [BUG?] bcachefs performance: read is way too slow when a file has no overwrite

David Wang
2024-09-22T08:47:54Z

At 2024-09-22 16:31:48, "David Wang" <00107082@163.com> wrote:
>>Hi,
>>

>btree_io write pattern, collected from btree_node_write_endio,
>is kind of uniform/flat distributed, not on block-friendly size
>boundaries (I think):
> +---------+------------+
> | sectors | percentage |
> +---------+------------+
> | 1 | 9.021% |
> | 3 | 1.440% |
> | 4 | 1.249% |
> | 2 | 1.157% |
> | 5 | 0.804% |
> | 6 | 0.409% |
> | 14 | 0.259% |
> | 15 | 0.253% |
> | 16 | 0.228% |
> | 7 | 0.226% |
> | 11 | 0.223% |
> | 10 | 0.223% |
> | 13 | 0.222% |
> | 9 | 0.213% |
> | 12 | 0.202% |
> | 41 | 0.194% |
> | 17 | 0.183% |
> | 8 | 0.182% |
> | 18 | 0.167% |
> | 20 | 0.167% |
> | 19 | 0.163% |
> | 21 | 0.160% |
> | 205 | 0.158% |
> | 22 | 0.145% |
> | 23 | 0.117% |
> | 24 | 0.093% |
> | 51 | 0.089% |
> | 25 | 0.080% |
> | 204 | 0.079% |
> +---------+------------+
>

Oops...wrong weight used to calculate percentage, it should be
+---------+------------+
| sectors | percentage |
+---------+------------+
| 1 | 45.105% |
| 3 | 7.200% |
| 4 | 6.244% |
| 2 | 5.785% |
| 5 | 4.018% |
| 6 | 2.045% |
| 14 | 1.296% |
| 15 | 1.264% |
| 16 | 1.141% |
| 7 | 1.129% |
| 11 | 1.117% |
| 10 | 1.113% |
| 13 | 1.111% |
| 9 | 1.065% |
| 12 | 1.011% |
| 41 | 0.971% |
| 17 | 0.913% |
| 8 | 0.912% |
| 18 | 0.836% |
| 20 | 0.835% |
| 19 | 0.812% |
| 21 | 0.799% |
| 205 | 0.791% |
| 22 | 0.724% |
| 23 | 0.587% |
| 24 | 0.465% |
| 51 | 0.443% |
| 25 | 0.398% |
| 204 | 0.396% |
+---------+------------+

David