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Commit 76b1e9b9 authored by Eliezer Tamir's avatar Eliezer Tamir Committed by David S. Miller
Browse files

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: default avatarEliezer Tamir <eliezer.tamir@linux.intel.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent cbf55001

fs/select.c

+20 −11
Original line number Diff line number Diff line
@@ -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))

		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))

		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

include/net/ll_poll.h

+18 −37
Original line number Diff line number Diff line
@@ -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 */