Commit 123698a5 authored Mar 10, 2023 by Nathan Huckleberry Committed by Greg Kroah-Hartman Apr 05, 2023

fsverity: Remove WQ_UNBOUND from fsverity read workqueue

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: 8a1d0f9c ("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>

parent 0eda2004

fs/verity/verify.c

+6 −6

Original line number	Diff line number	Diff line
		@@ -259,15 +259,15 @@ 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;