linux-kernel - Re: [PATCH 2/2] bcachefs: Set rebalance thread to SCHED

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Message-ID: <kycrjg4nlgwxb6b6wph3uolmh45t7ivmoi5jpy4pakvh74wnoo@wp7hlbcbtwyw>
Date: Fri, 15 Nov 2024 00:43:42 -0500
From: Kent Overstreet <kent.overstreet@...ux.dev>
To: Florian Schmaus <flo@...kplace.eu>
Cc: linux-bcachefs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] bcachefs: Set rebalance thread to SCHED_BATCH and
 nice 19

On Thu, Nov 14, 2024 at 10:06:48PM +0100, Florian Schmaus wrote:
> Set the rebalance thread's scheduling class to BATCH, which means it
> could experience a higher scheduling latency. However, it reduces
> preemption events of running threads.
> 
> And while the rebalance thread is ually not compute bound, it does
> cause a considerable amount of I/O. By increasing its nice level from
> 0 to 19 we also implicitly reduce the thread's best-effort I/O
> scheduling class level from 4 to 7. Therefore, the rebalance thread's
> I/O operations will be deprioritized over standard I/O operations.

Is there a patch 1/2?

> 
> Signed-off-by: Florian Schmaus <flo@...kplace.eu>
> ---
>  fs/bcachefs/rebalance.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/fs/bcachefs/rebalance.c b/fs/bcachefs/rebalance.c
> index 4adc74cd3f70..b26c68007c5a 100644
> --- a/fs/bcachefs/rebalance.c
> +++ b/fs/bcachefs/rebalance.c
> @@ -22,6 +22,7 @@
>  
>  #include <linux/freezer.h>
>  #include <linux/kthread.h>
> +#include <linux/sched.h>
>  #include <linux/sched/cputime.h>
>  
>  /* bch_extent_rebalance: */
> @@ -662,6 +663,8 @@ int bch2_rebalance_start(struct bch_fs *c)
>  	if (ret)
>  		return ret;
>  
> +	sched_set_batch(p, 19);
> +
>  	get_task_struct(p);
>  	rcu_assign_pointer(c->rebalance.thread, p);
>  	wake_up_process(p);
> -- 
> 2.45.2
>