From e249056c91a2f14ee40de2bf24cf72d8e68101f5 Mon Sep 17 00:00:00 2001 From: Pan Deng Date: Fri, 28 Feb 2025 10:00:59 +0800 Subject: [PATCH] fs: place f_ref to 3rd cache line in struct file to resolve false sharing 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 Link: https://lore.kernel.org/r/20250228020059.3023375-1-pan.deng@intel.com Tested-by: Lipeng Zhu Reviewed-by: Tianyou Li Reviewed-by: Tim Chen Signed-off-by: Christian Brauner --- include/linux/fs.h | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/include/linux/fs.h b/include/linux/fs.h index 70c985f3d787..9ab789cd1531 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -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 */ -- 2.49.0