diff options
| author | Mateusz Guzik <mjguzik@gmail.com> | 2024-06-13 02:12:15 +0200 |
|---|---|---|
| committer | Christian Brauner <brauner@kernel.org> | 2024-07-03 10:34:10 +0200 |
| commit | 18a5daf0e4974ded74b2ed8a6aed1da49bde356d (patch) | |
| tree | 79de3344b1322d61d55815ae85ce43fa776aa0e2 /include/linux/dcache.h | |
| parent | 267574dee6ae0da68f5b454a30ff276d45976cf8 (diff) | |
vfs: move d_lockref out of the area used by RCU lookup
Stock kernel scales worse than FreeBSD when doing a 20-way stat(2) on
the same tmpfs-backed file.
According to perf top:
38.09% lockref_put_return
26.08% lockref_get_not_dead
25.60% __d_lookup_rcu
0.89% clear_bhb_loop
__d_lookup_rcu is participating in cacheline ping pong due to the
embedded name sharing a cacheline with lockref.
Moving it out resolves the problem:
41.50% lockref_put_return
41.03% lockref_get_not_dead
1.54% clear_bhb_loop
benchmark (will-it-scale, Sapphire Rapids, tmpfs, ops/s):
FreeBSD:7219334
before: 5038006
after: 7842883 (+55%)
One minor remark: the 'after' result is unstable, fluctuating in the
range ~7.8 mln to ~9 mln during different runs.
Signed-off-by: Mateusz Guzik <mjguzik@gmail.com>
Link: https://lore.kernel.org/r/20240613001215.648829-3-mjguzik@gmail.com
Signed-off-by: Christian Brauner <brauner@kernel.org>
Diffstat (limited to 'include/linux/dcache.h')
| -rw-r--r-- | include/linux/dcache.h | 7 |
1 files changed, 6 insertions, 1 deletions
diff --git a/include/linux/dcache.h b/include/linux/dcache.h index bf53e3894aae..326dbccc3736 100644 --- a/include/linux/dcache.h +++ b/include/linux/dcache.h @@ -89,13 +89,18 @@ struct dentry { struct inode *d_inode; /* Where the name belongs to - NULL is * negative */ unsigned char d_iname[DNAME_INLINE_LEN]; /* small names */ + /* --- cacheline 1 boundary (64 bytes) was 32 bytes ago --- */ /* Ref lookup also touches following */ - struct lockref d_lockref; /* per-dentry lock and refcount */ const struct dentry_operations *d_op; struct super_block *d_sb; /* The root of the dentry tree */ unsigned long d_time; /* used by d_revalidate */ void *d_fsdata; /* fs-specific data */ + /* --- cacheline 2 boundary (128 bytes) --- */ + struct lockref d_lockref; /* per-dentry lock and refcount + * keep separate from RCU lookup area if + * possible! + */ union { struct list_head d_lru; /* LRU list */ |