diff options
| author | JonasZhou-oc <jonaszhou-oc@zhaoxin.com> | 2026-09-02 15:03:31 +0800 |
|---|---|---|
| committer | Theodore Ts'o <tytso@mit.edu> | 2026-10-08 11:07:51 -0400 |
| commit | b5501f970dbc039df1f7c720b7a481b62de125cd (patch) | |
| tree | bda700ac9ee958114cea833c2d84d611bca7a6be | |
| parent | 4a87cfb9b45ae07cd28bdc1ab9059ea73eab312e (diff) | |
jbd2: avoid false sharing with j_state_lock
is_journal_aborted() reads journal->j_flags from ext4 and JBD2 hot
paths. At the same time, transaction start and stop paths repeatedly
acquire and release j_state_lock. read_lock() and read_unlock() update
the lock word, so this traffic invalidates the cache line containing
j_flags.
On the tested x86-64 build, j_flags, j_errno, and j_state_lock occupy
the same 64-byte cache line. j_flags starts at offset 0, j_errno at
offset 8, and j_state_lock at offset 56.
Align j_state_lock to a cacheline boundary on SMP builds. This moves it
to offset 64 and prevents lock traffic from invalidating j_flags and
j_errno. Tests were run on Linux 7.3-rc1.
On a two-socket Intel Xeon Silver 4208 system with SMT disabled, CPUs
fixed at 2 GHz, and 16 stress-ng workers, ten-run average bogo-ops/s for
stress-ng.utime, stress-ng.access, stress-ng.file-ioctl, and
stress-ng.open increased by 9.60%, 5.42%, 2.05%, and 4.65%,
respectively. In separate five-run perf c2c measurements, average
Remote HITM samples for the affected j_flags/j_errno line decreased
from 1996, 2041, 1555, and 383 to zero, respectively.
Signed-off-by: JonasZhou-oc <jonaszhou-oc@zhaoxin.com>
Link: https://patch.msgid.link/20260902070331.820322-1-jonaszhou-oc@zhaoxin.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
| -rw-r--r-- | include/linux/jbd2.h | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/include/linux/jbd2.h b/include/linux/jbd2.h index 1b42fe47c26b..e3886963ba00 100644 --- a/include/linux/jbd2.h +++ b/include/linux/jbd2.h @@ -795,7 +795,7 @@ struct journal_s /** * @j_state_lock: Protect the various scalars in the journal. */ - rwlock_t j_state_lock; + rwlock_t j_state_lock ____cacheline_aligned_in_smp; /** * @j_barrier_count: |