Date:   Thu,  9 Mar 2023 13:37:41 -0800
Mime-Version: 1.0
Message-ID: <20230309213742.572091-1-nhuck@google.com>
Subject: [PATCH] fsverity: Remove WQ_UNBOUND from fsverity read workqueue
From:   Nathan Huckleberry <nhuck@google.com>
Cc:     Nathan Huckleberry <nhuck@google.com>,
        Eric Biggers <ebiggers@kernel.org>,
        "Theodore Y. Ts'o" <tytso@mit.edu>, fsverity@lists.linux.dev,
        linux-kernel@vger.kernel.org
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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.

This code was tested by running Android app startup benchmarks and
measuring how long the fsverity workqueue spent in the ready queue.

Before
Total workqueue scheduler latency: 553800us
After
Total workqueue scheduler latency: 18962us

Change-Id: I693efee541757851ed6d229430111cd763d39067
Signed-off-by: Nathan Huckleberry <nhuck@google.com>
---
 fs/verity/verify.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/verity/verify.c b/fs/verity/verify.c
index f50e3b5b52c9..e8ec37774d63 100644
--- a/fs/verity/verify.c
+++ b/fs/verity/verify.c
@@ -395,7 +395,7 @@ int __init fsverity_init_workqueue(void)
 	 * which blocks reads from completing, over regular application tasks.
 	 */
 	fsverity_read_workqueue = alloc_workqueue("fsverity_read_queue",
-						  WQ_UNBOUND | WQ_HIGHPRI,
+						  WQ_HIGHPRI,
 						  num_online_cpus());
 	if (!fsverity_read_workqueue)
 		return -ENOMEM;
-- 
2.40.0.rc1.284.g88254d51c5-goog