linux-kernel - [PATCH net-next v9 3/6] eventpoll: Trigger napi_busy_loop, if prefer_busy

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Message-Id: <20241109050245.191288-4-jdamato@fastly.com>
Date: Sat,  9 Nov 2024 05:02:33 +0000
From: Joe Damato <jdamato@...tly.com>
To: netdev@...r.kernel.org
Cc: corbet@....net,
	hdanton@...a.com,
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	pabeni@...hat.com,
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	Martin Karsten <mkarsten@...terloo.ca>,
	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: [PATCH net-next v9 3/6] 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>
Acked-by: Stanislav Fomichev <sdf@...ichev.me>
Reviewed-by: Sridhar Samudrala <sridhar.samudrala@...el.com>
---
 v1 -> v2:
   - Rebased to apply now that commit b9ca079dd6b0 ("eventpoll: Annotate
     data-race of busy_poll_usecs") has been picked up from VFS.

 fs/eventpoll.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 1ae4542f0bd8..f9e0d9307dad 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 !!READ_ONCE(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