From: Nathan Huckleberry nhuck@google.com
commit f959325e6ac3f499450088b8d9c626d1177be160 upstream.
WQ_UNBOUND causes significant scheduler latency on ARM64/Android. This is problematic for latency sensitive workloads, like I/O post-processing.
Removing WQ_UNBOUND gives a 96% reduction in fsverity workqueue related scheduler latency and improves app cold startup times by ~30ms. WQ_UNBOUND was also removed from the dm-verity workqueue for the same reason [1].
This code was tested by running Android app startup benchmarks and measuring how long the fsverity workqueue spent in the runnable state.
Before Total workqueue scheduler latency: 553800us After Total workqueue scheduler latency: 18962us
[1]: https://lore.kernel.org/all/20230202012348.885402-1-nhuck@google.com/
Signed-off-by: Nathan Huckleberry nhuck@google.com Fixes: 8a1d0f9cacc9 ("fs-verity: add data verification hooks for ->readpages()") Cc: stable@vger.kernel.org Link: https://lore.kernel.org/r/20230310193325.620493-1-nhuck@google.com Signed-off-by: Eric Biggers ebiggers@google.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/verity/verify.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-)
--- a/fs/verity/verify.c +++ b/fs/verity/verify.c @@ -279,15 +279,15 @@ EXPORT_SYMBOL_GPL(fsverity_enqueue_verif int __init fsverity_init_workqueue(void) { /* - * Use an unbound workqueue to allow bios to be verified in parallel - * even when they happen to complete on the same CPU. This sacrifices - * locality, but it's worthwhile since hashing is CPU-intensive. + * Use a high-priority workqueue to prioritize verification work, which + * blocks reads from completing, over regular application tasks. * - * Also use a high-priority workqueue to prioritize verification work, - * which blocks reads from completing, over regular application tasks. + * For performance reasons, don't use an unbound workqueue. Using an + * unbound workqueue for crypto operations causes excessive scheduler + * latency on ARM64. */ fsverity_read_workqueue = alloc_workqueue("fsverity_read_queue", - WQ_UNBOUND | WQ_HIGHPRI, + WQ_HIGHPRI, num_online_cpus()); if (!fsverity_read_workqueue) return -ENOMEM;