public-mirrors/linux
1
0
Fork 0
mirror of git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git synced 2025-08-05 16:54:27 +00:00
Code Issues Projects Releases Packages Wiki Activity Actions

fs: place f_ref to 3rd cache line in struct file to resolve false sharing

Browse source 
When running syscall pread in a high core count system, f_ref contends
with the reading of f_mode, f_op, f_mapping, f_inode, f_flags in the
same cache line.

This change places f_ref to the 3rd cache line where fields are not
updated as frequently as the 1st cache line, and the contention is
grealy reduced according to tests. In addition, the size of file
object is kept in 3 cache lines.

This change has been tested with rocksdb benchmark readwhilewriting case
in 1 socket 64 physical core 128 logical core baremetal machine, with
build config CONFIG_RANDSTRUCT_NONE=y
Command:
./db_bench --benchmarks="readwhilewriting" --threads $cnt --duration 60
The throughput(ops/s) is improved up to ~21%.
=====
thread		baseline	compare
16		 100%		 +1.3%
32		 100%		 +2.2%
64		 100%		 +7.2%
128		 100%		 +20.9%

It was also tested with UnixBench: syscall, fsbuffer, fstime,
fsdisk cases that has been used for file struct layout tuning, no
regression was observed.

Signed-off-by: Pan Deng <pan.deng@intel.com>
Link: https://lore.kernel.org/r/20250228020059.3023375-1-pan.deng@intel.com
Tested-by: Lipeng Zhu <lipeng.zhu@intel.com>
Reviewed-by: Tianyou Li <tianyou.li@intel.com>
Reviewed-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
This commit is contained in:
Pan Deng 2025-02-28 10:00:59 +08:00 • committed by Christian Brauner
parent d3a194d95f
commit e249056c91
No known key found for this signature in database
GPG key ID: 91C61BC06578DCA2
1 changed files with 4 additions and 4 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

8
include/linux/fs.h
View file

@ -1058,7 +1058,6 @@ static inline int ra_has_index(struct file_ra_state *ra, pgoff_t index)
/**
* struct file - Represents a file
* @f_ref: reference count
* @f_lock: Protects f_ep, f_flags. Must not be taken from IRQ context.
* @f_mode: FMODE_* flags often used in hotpaths
* @f_op: file operations
@ -1068,12 +1067,12 @@ static inline int ra_has_index(struct file_ra_state *ra, pgoff_t index)
* @f_flags: file flags
* @f_iocb_flags: iocb flags
* @f_cred: stashed credentials of creator/opener
* @f_owner: file owner
* @f_path: path of the file
* @f_pos_lock: lock protecting file position
* @f_pipe: specific to pipes
* @f_pos: file position
* @f_security: LSM security context of this file
* @f_owner: file owner
* @f_wb_err: writeback error
* @f_sb_err: per sb writeback errors
* @f_ep: link of all epoll hooks for this file
@ -1081,9 +1080,9 @@ static inline int ra_has_index(struct file_ra_state *ra, pgoff_t index)
* @f_llist: work queue entrypoint
* @f_ra: file's readahead state
* @f_freeptr: Pointer used by SLAB_TYPESAFE_BY_RCU file cache (don't touch.)
* @f_ref: reference count
*/
struct file {
file_ref_t f_ref;
spinlock_t f_lock;
fmode_t f_mode;
const struct file_operations *f_op;
@ -1093,6 +1092,7 @@ struct file {
unsigned int f_flags;
unsigned int f_iocb_flags;
const struct cred *f_cred;
struct fown_struct *f_owner;
/* --- cacheline 1 boundary (64 bytes) --- */
struct path f_path;
union {
@ -1106,7 +1106,6 @@ struct file {
void *f_security;
#endif
/* --- cacheline 2 boundary (128 bytes) --- */
struct fown_struct *f_owner;
errseq_t f_wb_err;
errseq_t f_sb_err;
#ifdef CONFIG_EPOLL
@ -1118,6 +1117,7 @@ struct file {
struct file_ra_state f_ra;
freeptr_t f_freeptr;
};
file_ref_t f_ref;
/* --- cacheline 3 boundary (192 bytes) --- */
} __randomize_layout
__attribute__((aligned(4))); /* lest something weird decides that 2 is OK */