[PATCH net-next v4 1/3] eventpoll: support busy poll per epoll instance

Joe Damato
2024-01-31T01:47:46Z

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.

Note that this change uses an xor: either per epoll instance busy polling
is enabled on the epoll instance or system wide epoll is enabled. Enabling
both is disallowed.

Signed-off-by: Joe Damato <jdamato@fastly.com>
---
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
+ 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