blob: a59001e85da83220d16623c6bbf649df9e5f4c0e [file] [log] [blame]
From: Sebastian Andrzej Siewior <>
Date: Thu, 8 Sep 2016 18:33:52 +0200
Subject: [PATCH] fs/dcache: resched/chill only if we make no progress
Upstream commit 47be61845c77 ("fs/dcache.c: avoid soft-lockup in
dput()") changed the condition _when_ cpu_relax() / cond_resched() was
invoked. This change was adapted in -RT into mostly the same thing
except that if cond_resched() did nothing we had to do cpu_chill() to
force the task off CPU for a tiny little bit in case the task had RT
priority and did not want to leave the CPU.
This change resulted in a performance regression (in my testcase the
build time on /dev/shm increased from 19min to 24min). The reason is
that with this change cpu_chill() was invoked even dput() made progress
(dentry_kill() returned a different dentry) instead only if we were
trying this operation on the same dentry over and over again.
This patch brings back to the old behavior back to cond_resched() &
chill if we make no progress. A little improvement is to invoke
cpu_chill() only if we are a RT task (and avoid the sleep otherwise).
Otherwise the scheduler should remove us from the CPU if we make no
Signed-off-by: Sebastian Andrzej Siewior <>
fs/dcache.c | 19 +++++++++++++------
1 file changed, 13 insertions(+), 6 deletions(-)
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -40,6 +40,8 @@
#include <linux/ratelimit.h>
#include <linux/list_lru.h>
#include <linux/kasan.h>
+#include <linux/sched/rt.h>
+#include <linux/sched/deadline.h>
#include "internal.h"
#include "mount.h"
@@ -748,6 +750,8 @@ static inline bool fast_dput(struct dent
void dput(struct dentry *dentry)
+ struct dentry *parent;
if (unlikely(!dentry))
@@ -784,14 +788,17 @@ void dput(struct dentry *dentry)
- dentry = dentry_kill(dentry);
- if (dentry) {
+ parent = dentry_kill(dentry);
+ if (parent) {
int r;
- /* the task with the highest priority won't schedule */
- r = cond_resched();
- if (!r)
- cpu_chill();
+ if (parent == dentry) {
+ /* the task with the highest priority won't schedule */
+ r = cond_resched();
+ if (!r && (rt_task(current) || dl_task(current)))
+ cpu_chill();
+ } else
+ dentry = parent;
goto repeat;