From: Yuqi Jin <jinyuqi@xxxxxxxxxx>
__fget_files does check the @f_mode with mask variable and will do some
atomic operations on @f_count while both are on the same cacheline.
Many CPU cores do file access and it will cause much conflicts on @f_count.
If we could make the two members into different cachelines, it shall relax
the siutations.
We have tested this on ARM64 and X86, the result is as follows:
Syscall of unixbench has been run on Huawei Kunpeng920 with this patch:
24 x System Call Overhead 1
System Call Overhead 3160841.4 lps (10.0 s, 1 samples)
System Benchmarks Partial Index BASELINE RESULT INDEX
System Call Overhead 15000.0 3160841.4 2107.2
========
System Benchmarks Index Score (Partial Only) 2107.2
Without this patch:
24 x System Call Overhead 1
System Call Overhead 2222456.0 lps (10.0 s, 1 samples)
System Benchmarks Partial Index BASELINE RESULT INDEX
System Call Overhead 15000.0 2222456.0 1481.6
========
System Benchmarks Index Score (Partial Only) 1481.6
And on Intel 6248 platform with this patch:
40 CPUs in system; running 24 parallel copies of tests
System Call Overhead 4288509.1 lps (10.0 s, 1 samples)
System Benchmarks Partial Index BASELINE RESULT INDEX
System Call Overhead 15000.0 4288509.1 2859.0
========
System Benchmarks Index Score (Partial Only) 2859.0
Without this patch:
40 CPUs in system; running 24 parallel copies of tests
System Call Overhead 3666313.0 lps (10.0 s, 1 samples)
System Benchmarks Partial Index BASELINE RESULT INDEX
System Call Overhead 15000.0 3666313.0 2444.2
========
System Benchmarks Index Score (Partial Only) 2444.2
Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Yuqi Jin <jinyuqi@xxxxxxxxxx>
Signed-off-by: Shaokun Zhang <zhangshaokun@xxxxxxxxxxxxx>
---
include/linux/fs.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 4f6f59b4f22a..90e76283f0fd 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -953,7 +953,6 @@ struct file {
*/
spinlock_t f_lock;
enum rw_hint f_write_hint;
- atomic_long_t f_count;
unsigned int f_flags;
fmode_t f_mode;
struct mutex f_pos_lock;
@@ -976,6 +975,7 @@ struct file {
#endif /* #ifdef CONFIG_EPOLL */
struct address_space *f_mapping;
errseq_t f_wb_err;
+ atomic_long_t f_count;
} __randomize_layout
__attribute__((aligned(4))); /* lest something weird decides that 2 is OK */
--
2.7.4
