On Thu, Feb 08, 2024 at 06:46:25PM +0100, Eric Dumazet wrote:

On Mon, Feb 5, 2024 at 10:05 PM Joe Damato [off-list ref] wrote:

quoted

Allow busy polling on a per-epoll context basis. The per-epoll context
usec timeout value is preferred, but the pre-existing system wide sysctl
value is still supported if it specified.

Signed-off-by: Joe Damato <redacted>
---
 fs/eventpoll.c | 49 +++++++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 45 insertions(+), 4 deletions(-)

diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 3534d36a1474..ce75189d46df 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c

@@ -227,6 +227,8 @@ struct eventpoll {
 #ifdef CONFIG_NET_RX_BUSY_POLL
        /* used to track busy poll napi_id */
        unsigned int napi_id;
+       /* busy poll timeout */
+       u64 busy_poll_usecs;
 #endif

 #ifdef CONFIG_DEBUG_LOCK_ALLOC

@@ -386,12 +388,44 @@ static inline int ep_events_available(struct eventpoll *ep)
                READ_ONCE(ep->ovflist) != EP_UNACTIVE_PTR;
 }

+/**
+ * busy_loop_ep_timeout - check if busy poll has timed out. The timeout value
+ * from the epoll instance ep is preferred, but if it is not set fallback to
+ * the system-wide global via busy_loop_timeout.
+ *
+ * @start_time: The start time used to compute the remaining time until timeout.
+ * @ep: Pointer to the eventpoll context.
+ *
+ * Return: true if the timeout has expired, false otherwise.
+ */
+static inline bool busy_loop_ep_timeout(unsigned long start_time, struct eventpoll *ep)
+{
+#ifdef CONFIG_NET_RX_BUSY_POLL

It seems this local helper is only called from code compiled when
CONFIG_NET_RX_BUSY_POLL
is set.

Not sure why you need an #ifdef here.

Thanks, you are right.

I'll move this down to be within CONFIG_NET_RX_BUSY_POLL and get rid of the
#ifdef for the v7.

Thanks for your review.
 

quoted

+       unsigned long bp_usec = READ_ONCE(ep->busy_poll_usecs);
+
+       if (bp_usec) {
+               unsigned long end_time = start_time + bp_usec;
+               unsigned long now = busy_loop_current_time();
+
+               return time_after(now, end_time);
+       } else {
+               return busy_loop_timeout(start_time);
+       }
+#endif
+       return true;
+}
+
 #ifdef CONFIG_NET_RX_BUSY_POLL
+static bool ep_busy_loop_on(struct eventpoll *ep)
+{
+       return !!ep->busy_poll_usecs || net_busy_loop_on();
+}
+
 static bool ep_busy_loop_end(void *p, unsigned long start_time)
 {
        struct eventpoll *ep = p;

-       return ep_events_available(ep) || busy_loop_timeout(start_time);
+       return ep_events_available(ep) || busy_loop_ep_timeout(start_time, ep);
 }

 /*

@@ -404,7 +438,7 @@ static bool ep_busy_loop(struct eventpoll *ep, int nonblock)
 {
        unsigned int napi_id = READ_ONCE(ep->napi_id);

-       if ((napi_id >= MIN_NAPI_ID) && net_busy_loop_on()) {
+       if ((napi_id >= MIN_NAPI_ID) && ep_busy_loop_on(ep)) {
                napi_busy_loop(napi_id, nonblock ? NULL : ep_busy_loop_end, ep, false,
                               BUSY_POLL_BUDGET);
                if (ep_events_available(ep))

@@ -430,7 +464,8 @@ static inline void ep_set_busy_poll_napi_id(struct epitem *epi)
        struct socket *sock;
        struct sock *sk;

-       if (!net_busy_loop_on())
+       ep = epi->ep;
+       if (!ep_busy_loop_on(ep))
                return;

        sock = sock_from_file(epi->ffd.file);

@@ -442,7 +477,6 @@ static inline void ep_set_busy_poll_napi_id(struct epitem *epi)
                return;

        napi_id = READ_ONCE(sk->sk_napi_id);
-       ep = epi->ep;

        /* Non-NAPI IDs can be rejected
         *      or

@@ -466,6 +500,10 @@ static inline void ep_set_busy_poll_napi_id(struct epitem *epi)
 {
 }

+static inline bool ep_busy_loop_on(struct eventpoll *ep)
+{
+       return false;
+}
 #endif /* CONFIG_NET_RX_BUSY_POLL */

 /*

@@ -2058,6 +2096,9 @@ static int do_epoll_create(int flags)
                error = PTR_ERR(file);
                goto out_free_fd;
        }
+#ifdef CONFIG_NET_RX_BUSY_POLL
+       ep->busy_poll_usecs = 0;
+#endif
        ep->file = file;
        fd_install(fd, file);
        return fd;
--

2.25.1