eventpoll: Trigger napi_busy_loop, if prefer_busy_poll is set

JIRA: https://issues.redhat.com/browse/RHEL-77189
Upstream Status: linux.git

commit ab5b28b
Author: Martin Karsten <mkarsten@uwaterloo.ca>
Date:   Sat Nov 9 05:02:33 2024 +0000

    eventpoll: Trigger napi_busy_loop, if prefer_busy_poll is set

    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@uwaterloo.ca>
    Co-developed-by: Joe Damato <jdamato@fastly.com>
    Signed-off-by: Joe Damato <jdamato@fastly.com>
    Tested-by: Joe Damato <jdamato@fastly.com>
    Tested-by: Martin Karsten <mkarsten@uwaterloo.ca>
    Acked-by: Stanislav Fomichev <sdf@fomichev.me>
    Reviewed-by: Sridhar Samudrala <sridhar.samudrala@intel.com>
    Link: https://patch.msgid.link/20241109050245.191288-4-jdamato@fastly.com
    Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Signed-off-by: Antoine Tenart <atenart@redhat.com>

Author: atenart

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)