Re: [PATCH 2/2] bcachefs: set rebalance thread to SCHED_BATCH and nice 19

[Florian Schmaus]

On 14/01/2025 14.29, Christian Loehle wrote:

On 1/14/25 12:47, Florian Schmaus wrote:

While the rebalance thread is isually not compute bound, it does cause

s/isually/usually

a considerable amount of I/O. Since "reducing" the nice level from 0
to 19, also implicitly reduces the threads best-effort I/O scheduling
class level from 4 to 7, the reblance thread's I/O will be depriotized

s/depriotized/deprioritized/

over normal I/O.

Furthermore, we set the rebalance thread's scheduling class to BATCH,
which means that it will potentially receive a higher scheduling
latency. Making room for threads that need a low
schedulinglatency (e.g., interactive onces).

s/schedulinglatency/
I know nothing about bcachefs internals, but could this also be a problem?
The rebalance thread might not run for O(second) or so?

- Florian

Thanks for the review, much appreciated. I have adjusted the commit message in my branch [1]. Bcachefs rebalance task is not really scheduling latency sensitive, unlike bcachefs' copygc task, so it is fine to run it under BATCH. 1: https://github.com/Flowdalic/linux/tree/bcachefs-rebalance-set-sched-batch

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