linux-kernel - [RFC net-next 4/5] eventpoll: Trigger napi_busy_loop, if prefer_busy

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Message-Id: <20240812125717.413108-5-jdamato@fastly.com>
Date: Mon, 12 Aug 2024 12:57:07 +0000
From: Joe Damato <jdamato@...tly.com>
To: netdev@...r.kernel.org
Cc: mkarsten@...terloo.ca,
	amritha.nambiar@...el.com,
	sridhar.samudrala@...el.com,
	sdf@...ichev.me,
	Joe Damato <jdamato@...tly.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Christian Brauner <brauner@...nel.org>,
	Jan Kara <jack@...e.cz>,
	linux-fsdevel@...r.kernel.org (open list:FILESYSTEMS (VFS and infrastructure)),
	linux-kernel@...r.kernel.org (open list)
Subject: [RFC net-next 4/5] eventpoll: Trigger napi_busy_loop, if prefer_busy_poll is set

From: Martin Karsten <mkarsten@...terloo.ca>

Setting prefer_busy_poll now leads to an effectively nonblocking
iteration though napi_busy_loop, even when busy_poll_usecs is 0.

Signed-off-by: Martin Karsten <mkarsten@...terloo.ca>
Co-developed-by: Joe Damato <jdamato@...tly.com>
Signed-off-by: Joe Damato <jdamato@...tly.com>
Tested-by: Joe Damato <jdamato@...tly.com>
Tested-by: Martin Karsten <mkarsten@...terloo.ca>
---
 fs/eventpoll.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index f53ca4f7fced..cc47f72005ed 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -420,7 +420,9 @@ static bool busy_loop_ep_timeout(unsigned long start_time,
 
 static bool ep_busy_loop_on(struct eventpoll *ep)
 {
-	return !!ep->busy_poll_usecs || net_busy_loop_on();
+	return !!READ_ONCE(ep->busy_poll_usecs) ||
+	       READ_ONCE(ep->prefer_busy_poll) ||
+	       net_busy_loop_on();
 }
 
 static bool ep_busy_loop_end(void *p, unsigned long start_time)
-- 
2.25.1