This is a note to let you know that I've just added the patch titled
fsverity: Remove WQ_UNBOUND from fsverity read workqueue
to the 6.2-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
fsverity-remove-wq_unbound-from-fsverity-read-workqueue.patch
and it can be found in the queue-6.2 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From f959325e6ac3f499450088b8d9c626d1177be160 Mon Sep 17 00:00:00 2001
From: Nathan Huckleberry <nhuck@xxxxxxxxxx>
Date: Fri, 10 Mar 2023 11:33:25 -0800
Subject: fsverity: Remove WQ_UNBOUND from fsverity read workqueue
From: Nathan Huckleberry <nhuck@xxxxxxxxxx>
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@xxxxxxxxxx/
Signed-off-by: Nathan Huckleberry <nhuck@xxxxxxxxxx>
Fixes: 8a1d0f9cacc9 ("fs-verity: add data verification hooks for ->readpages()")
Cc: stable@xxxxxxxxxxxxxxx
Link: https://lore.kernel.org/r/20230310193325.620493-1-nhuck@xxxxxxxxxx
Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
fs/verity/verify.c | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)
--- a/fs/verity/verify.c
+++ b/fs/verity/verify.c
@@ -269,15 +269,15 @@ 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;
Patches currently in stable-queue which might be from nhuck@xxxxxxxxxx are
queue-6.2/fsverity-remove-wq_unbound-from-fsverity-read-workqueue.patch
