lkml.org 
[lkml]   [2014]   [Jun]   [17]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH v2 2/2] mm, thp: replace smp_mb after atomic_add by smp_mb__after_atomic
Date
In some architectures like x86, atomic_add() is a full memory
barrier. In that case, an additional smp_mb() is just a waste of time.
This patch replaces that smp_mb() by smp_mb__after_atomic() which
will avoid the redundant memory barrier in some architectures.

With a 3.16-rc1 based kernel, this patch reduced the execution time
of breaking 1000 transparent huge pages from 38,245us to 30,964us. A
reduction of 19% which is quite sizeable. It also reduces the %cpu
time of the __split_huge_page_refcount function in the perf profile
from 2.18% to 1.15%.

Signed-off-by: Waiman Long <Waiman.Long@hp.com>
---
mm/huge_memory.c | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index be84c71..e2ee131 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1650,7 +1650,7 @@ static void __split_huge_page_refcount(struct page *page,
&page_tail->_count);

/* after clearing PageTail the gup refcount can be released */
- smp_mb();
+ smp_mb__after_atomic();

/*
* retain hwpoison flag of the poisoned tail page:
--
1.7.1


\
 
 \ /
  Last update: 2014-06-18 04:41    [W:0.100 / U:1.592 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site