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

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Message-ID: <20241114210649.71377-2-flo@geekplace.eu>
Date: Thu, 14 Nov 2024 22:06:48 +0100
From: Florian Schmaus <flo@...kplace.eu>
To: Kent Overstreet <kent.overstreet@...ux.dev>
Cc: Florian Schmaus <flo@...kplace.eu>,
	linux-bcachefs@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH 2/2] bcachefs: Set rebalance thread to SCHED_BATCH and nice 19

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.

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