From: Nathan Huckleberry <nhuck@google.com>
Date: Fri, 10 Mar 2023 11:33:25 -0800
Subject: [PATCH] fsverity: Remove WQ_UNBOUND from fsverity read workqueue
References: bsc#1012628
Patch-mainline: 6.2.9
Git-commit: f959325e6ac3f499450088b8d9c626d1177be160

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>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
 fs/verity/verify.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/fs/verity/verify.c b/fs/verity/verify.c
index 961ba248..ffac380b 100644
--- a/fs/verity/verify.c
+++ b/fs/verity/verify.c
@@ -269,15 +269,15 @@ EXPORT_SYMBOL_GPL(fsverity_enqueue_verify_work);
 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;
-- 
2.35.3