In the syscall test of UnixBench, performance regression occurred
due to false sharing.
The lock and atomic members, including file::f_lock, file::f_count
and file::f_pos_lock are highly contended and frequently updated
in the high-concurrency test scenarios. perf c2c indentified one
affected read access, file::f_op.
To prevent false sharing, the layout of file struct is changed as
following
(A) f_lock, f_count and f_pos_lock are put together to share the
same cache line.
(B) The read mostly members, including f_path, f_inode, f_op are
put into a separate cache line.
(C) f_mode is put together with f_count, since they are used
frequently at the same time.
The optimization has been validated in the syscall test of
UnixBench. performance gain is 30~50%, when the number of parallel
jobs is 16.
Signed-off-by: chenzhiyin <zhiyin.chen@xxxxxxxxx>
---
include/linux/fs.h | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 21a981680856..01c55e3a1b96 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -962,23 +962,23 @@ struct file {
struct rcu_head f_rcuhead;
unsigned int f_iocb_flags;
};
- struct path f_path;
- struct inode *f_inode; /* cached value */
- const struct file_operations *f_op;
/*
* Protects f_ep, f_flags.
* Must not be taken from IRQ context.
*/
spinlock_t f_lock;
- atomic_long_t f_count;
- unsigned int f_flags;
fmode_t f_mode;
+ atomic_long_t f_count;
struct mutex f_pos_lock;
+ unsigned int f_flags;
loff_t f_pos;
struct fown_struct f_owner;
const struct cred *f_cred;
struct file_ra_state f_ra;
+ struct path f_path;
+ struct inode *f_inode; /* cached value */
+ const struct file_operations *f_op;
u64 f_version;
#ifdef CONFIG_SECURITY
--
2.39.1
