eventpoll: Add per-epoll prefer busy poll option

When using epoll-based busy poll, the prefer_busy_poll option is hardcoded
to false. Users may want to enable prefer_busy_poll to be used in
conjunction with gro_flush_timeout and defer_hard_irqs_count to keep device
IRQs masked.

Other busy poll methods allow enabling or disabling prefer busy poll via
SO_PREFER_BUSY_POLL, but epoll-based busy polling uses a hardcoded value.

Fix this edge case by adding support for a per-epoll context
prefer_busy_poll option. The default is false, as it was hardcoded before
this change.

Signed-off-by: Joe Damato <jdamato@fastly.com>
Acked-by: Stanislav Fomichev <sdf@google.com>
Reviewed-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index ed83ae33dd45c9b6847b33991a0e0bfc54ab7f7a..1b8d01af0c2cf120dfd54bb7deb7c3c624b2b0b4 100644 (file)
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -231,6 +231,7 @@ struct eventpoll {
        u32 busy_poll_usecs;
        /* busy poll packet budget */
        u16 busy_poll_budget;
+       bool prefer_busy_poll;
 #endif
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
@@ -438,13 +439,14 @@ static bool ep_busy_loop(struct eventpoll *ep, int nonblock)
 {
        unsigned int napi_id = READ_ONCE(ep->napi_id);
        u16 budget = READ_ONCE(ep->busy_poll_budget);
+       bool prefer_busy_poll = READ_ONCE(ep->prefer_busy_poll);
 
        if (!budget)
                budget = BUSY_POLL_BUDGET;
 
        if (napi_id >= MIN_NAPI_ID && ep_busy_loop_on(ep)) {
-               napi_busy_loop(napi_id, nonblock ? NULL : ep_busy_loop_end, ep, false,
-                              budget);
+               napi_busy_loop(napi_id, nonblock ? NULL : ep_busy_loop_end,
+                              ep, prefer_busy_poll, budget);
                if (ep_events_available(ep))
                        return true;
                /*
@@ -2098,6 +2100,7 @@ static int do_epoll_create(int flags)
 #ifdef CONFIG_NET_RX_BUSY_POLL
        ep->busy_poll_usecs = 0;
        ep->busy_poll_budget = 0;
+       ep->prefer_busy_poll = false;
 #endif
        ep->file = file;
        fd_install(fd, file);