netdev - [PATCH] percpu: add a schedule point in pcpu_balance

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Date:   Fri, 23 Feb 2018 08:12:42 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Tejun Heo <tj@...nel.org>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>
Subject: [PATCH] percpu: add a schedule point in pcpu_balance_workfn()

From: Eric Dumazet <edumazet@...gle.com>

When a large BPF percpu map is destroyed, I have seen
pcpu_balance_workfn() holding cpu for hundreds of milliseconds.

On KASAN config and 112 hyperthreads, average time to destroy a chunk
is ~4 ms.

[ 2489.841376] destroy chunk 1 in 4148689 ns
...
[ 2490.093428] destroy chunk 32 in 4072718 ns

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 mm/percpu.c |    1 +
 1 file changed, 1 insertion(+)

diff --git a/mm/percpu.c b/mm/percpu.c
index 50e7fdf84055151d8c7e8bb220f7a73e96b7f3e4..d40dfb597ffce2656220257f0227219ab917135b 100644
--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -1600,6 +1600,7 @@ static void pcpu_balance_workfn(struct work_struct *work)
 			spin_unlock_irq(&pcpu_lock);
 		}
 		pcpu_destroy_chunk(chunk);
+		cond_resched();
 	}
 
 	/*