net/fs: change busy poll time accounting

Suggested by Linus:
Changed time accounting for busy-poll:
- Make it microsecond based.
- Use unsigned longs.
- Revert back to use time_after instead of time_in_range.
Reorder poll/select busy loop conditions:
- Clear busy_flag after one time we can't busy-poll.
- Only init busy_end if we actually are going to busy-poll.
Added one more missing need_resched() test.

Signed-off-by: Eliezer Tamir <eliezer.tamir@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/fs/select.c b/fs/select.c
index 25cac5faf6d69a4aea55eb3408b544afc104920f..50a804b6839fc1e2d58dc9dc7612b1403f7eb1b9 100644 (file)
--- a/fs/select.c
+++ b/fs/select.c
@@ -403,8 +403,7 @@ int do_select(int n, fd_set_bits *fds, struct timespec *end_time)
        int retval, i, timed_out = 0;
        unsigned long slack = 0;
        unsigned int busy_flag = net_busy_loop_on() ? POLL_BUSY_LOOP : 0;
-       u64 busy_start = busy_loop_start_time(busy_flag);
-       u64 busy_end = busy_loop_end_time();
+       unsigned long busy_end = 0;
 
        rcu_read_lock();
        retval = max_select_fd(n, fds);
@@ -506,9 +505,15 @@ int do_select(int n, fd_set_bits *fds, struct timespec *end_time)
                }
 
                /* only if found POLL_BUSY_LOOP sockets && not out of time */
-               if (!need_resched() && can_busy_loop &&
-                   busy_loop_range(busy_start, busy_end))
-                       continue;
+               if (can_busy_loop && !need_resched()) {
+                       if (!busy_end) {
+                               busy_end = busy_loop_end_time();
+                               continue;
+                       }
+                       if (!busy_loop_timeout(busy_end))
+                               continue;
+               }
+               busy_flag = 0;
 
                /*
                 * If this is the first loop and we have a timeout
@@ -780,9 +785,7 @@ static int do_poll(unsigned int nfds,  struct poll_list *list,
        int timed_out = 0, count = 0;
        unsigned long slack = 0;
        unsigned int busy_flag = net_busy_loop_on() ? POLL_BUSY_LOOP : 0;
-       u64 busy_start = busy_loop_start_time(busy_flag);
-       u64 busy_end = busy_loop_end_time();
-
+       unsigned long busy_end = 0;
 
        /* Optimise the no-wait case */
        if (end_time && !end_time->tv_sec && !end_time->tv_nsec) {
@@ -834,9 +837,15 @@ static int do_poll(unsigned int nfds,  struct poll_list *list,
                        break;
 
                /* only if found POLL_BUSY_LOOP sockets && not out of time */
-               if (!need_resched() && can_busy_loop &&
-                   busy_loop_range(busy_start, busy_end))
-                       continue;
+               if (can_busy_loop && !need_resched()) {
+                       if (!busy_end) {
+                               busy_end = busy_loop_end_time();
+                               continue;
+                       }
+                       if (!busy_loop_timeout(busy_end))
+                               continue;
+               }
+               busy_flag = 0;
 
                /*
                 * If this is the first loop and we have a timeout

diff --git a/include/net/ll_poll.h b/include/net/ll_poll.h
index f14dd88dafc87569fed73b835015ae5546f670e5..76f03408774388101a0d31e4f20187bb28cff525 100644 (file)
--- a/include/net/ll_poll.h
+++ b/include/net/ll_poll.h
@@ -47,7 +47,7 @@ static inline bool net_busy_loop_on(void)
  * we only care that the average is bounded
  */
 #ifdef CONFIG_DEBUG_PREEMPT
-static inline u64 busy_loop_sched_clock(void)
+static inline u64 busy_loop_us_clock(void)
 {
        u64 rc;
 
@@ -55,37 +55,24 @@ static inline u64 busy_loop_sched_clock(void)
        rc = sched_clock();
        preempt_enable_no_resched_notrace();
 
-       return rc;
+       return rc >> 10;
 }
 #else /* CONFIG_DEBUG_PREEMPT */
-static inline u64 busy_loop_sched_clock(void)
+static inline u64 busy_loop_us_clock(void)
 {
-       return sched_clock();
+       return sched_clock() >> 10;
 }
 #endif /* CONFIG_DEBUG_PREEMPT */
 
-/* we don't mind a ~2.5% imprecision so <<10 instead of *1000
- * sk->sk_ll_usec is a u_int so this can't overflow
- */
-static inline u64 sk_busy_loop_end_time(struct sock *sk)
+static inline unsigned long sk_busy_loop_end_time(struct sock *sk)
 {
-       return (u64)ACCESS_ONCE(sk->sk_ll_usec) << 10;
+       return busy_loop_us_clock() + ACCESS_ONCE(sk->sk_ll_usec);
 }
 
-/* in poll/select we use the global sysctl_net_ll_poll value
- * only call sched_clock() if enabled
- */
-static inline u64 busy_loop_end_time(void)
-{
-       return (u64)ACCESS_ONCE(sysctl_net_ll_poll) << 10;
-}
-
-/* if flag is not set we don't need to know the time
- * so we want to avoid a potentially expensive sched_clock()
- */
-static inline u64 busy_loop_start_time(unsigned int flag)
+/* in poll/select we use the global sysctl_net_ll_poll value */
+static inline unsigned long busy_loop_end_time(void)
 {
-       return flag ? busy_loop_sched_clock() : 0;
+       return busy_loop_us_clock() + ACCESS_ONCE(sysctl_net_ll_poll);
 }
 
 static inline bool sk_can_busy_loop(struct sock *sk)
@@ -94,12 +81,12 @@ static inline bool sk_can_busy_loop(struct sock *sk)
               !need_resched() && !signal_pending(current);
 }
 
-/* careful! time_in_range64 will evaluate now twice */
-static inline bool busy_loop_range(u64 start_time, u64 run_time)
+
+static inline bool busy_loop_timeout(unsigned long end_time)
 {
-       u64 now = busy_loop_sched_clock();
+       unsigned long now = busy_loop_us_clock();
 
-       return time_in_range64(now, start_time, start_time + run_time);
+       return time_after(now, end_time);
 }
 
 /* when used in sock_poll() nonblock is known at compile time to be true
@@ -107,8 +94,7 @@ static inline bool busy_loop_range(u64 start_time, u64 run_time)
  */
 static inline bool sk_busy_loop(struct sock *sk, int nonblock)
 {
-       u64 start_time = busy_loop_start_time(!nonblock);
-       u64 end_time = sk_busy_loop_end_time(sk);
+       unsigned long end_time = !nonblock ? sk_busy_loop_end_time(sk) : 0;
        const struct net_device_ops *ops;
        struct napi_struct *napi;
        int rc = false;
@@ -139,7 +125,7 @@ static inline bool sk_busy_loop(struct sock *sk, int nonblock)
                                         LINUX_MIB_LOWLATENCYRXPACKETS, rc);
 
        } while (!nonblock && skb_queue_empty(&sk->sk_receive_queue) &&
-                busy_loop_range(start_time, end_time));
+                !need_resched() && !busy_loop_timeout(end_time));
 
        rc = !skb_queue_empty(&sk->sk_receive_queue);
 out:
@@ -165,12 +151,7 @@ static inline unsigned long net_busy_loop_on(void)
        return 0;
 }
 
-static inline u64 busy_loop_start_time(unsigned int flag)
-{
-       return 0;
-}
-
-static inline u64 busy_loop_end_time(void)
+static inline unsigned long busy_loop_end_time(void)
 {
        return 0;
 }
@@ -193,9 +174,9 @@ static inline void sk_mark_ll(struct sock *sk, struct sk_buff *skb)
 {
 }
 
-static inline bool busy_loop_range(u64 start_time, u64 run_time)
+static inline bool busy_loop_timeout(unsigned long end_time)
 {
-       return false;
+       return true;
 }
 
 #endif /* CONFIG_NET_LL_RX_POLL */