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Commit 91e2fd33 authored by Eliezer Tamir's avatar Eliezer Tamir Committed by David S. Miller
Browse files

net: avoid calling sched_clock when LLS is off 



Change Low Latency Sockets code for select and poll so that
when LLS is disabled sched_clock() is never called.

Also, avoid sending POLL_LL to sockets if disabled.

Reported-by: default avatarAndi Kleen <andi@firstfloor.org>
Signed-off-by: default avatarEliezer Tamir <eliezer.tamir@linux.intel.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent ad6276e0

fs/select.c

+7 −4
Original line number Diff line number Diff line
@@ -402,7 +402,7 @@ int do_select(int n, fd_set_bits *fds, struct timespec *end_time) 
	poll_table *wait;

	int retval, i, timed_out = 0;

	unsigned long slack = 0;

	unsigned int ll_flag = POLL_LL;

	unsigned int ll_flag = ll_get_flag();

	u64 ll_time = ll_end_time();



	rcu_read_lock();
@@ -497,7 +497,8 @@ int do_select(int n, fd_set_bits *fds, struct timespec *end_time) 
			break;

		}



		if (can_ll && can_poll_ll(ll_time))

		/* only if on, have sockets with POLL_LL and not out of time */

		if (ll_flag && can_ll && can_poll_ll(ll_time))

			continue;



		/*
@@ -768,7 +769,7 @@ static int do_poll(unsigned int nfds, struct poll_list *list, 
	ktime_t expire, *to = NULL;

	int timed_out = 0, count = 0;

	unsigned long slack = 0;

	unsigned int ll_flag = POLL_LL;

	unsigned int ll_flag = ll_get_flag();

	u64 ll_time = ll_end_time();



	/* Optimise the no-wait case */
@@ -817,8 +818,10 @@ static int do_poll(unsigned int nfds, struct poll_list *list, 
		if (count || timed_out)

			break;



		if (can_ll && can_poll_ll(ll_time))

		/* only if on, have sockets with POLL_LL and not out of time */

		if (ll_flag && can_ll && can_poll_ll(ll_time))

			continue;



		/*

		 * If this is the first loop and we have a timeout

		 * given, then we convert to ktime_t and set the to

include/net/ll_poll.h

+15 −2
Original line number Diff line number Diff line
@@ -37,6 +37,11 @@ extern unsigned int sysctl_net_ll_poll __read_mostly; 
#define LL_FLUSH_FAILED		-1

#define LL_FLUSH_BUSY		-2



static inline unsigned int ll_get_flag(void)

{

	return sysctl_net_ll_poll ? POLL_LL : 0;

}



/* a wrapper to make debug_smp_processor_id() happy

 * we can use sched_clock() because we don't care much about precision

 * we only care that the average is bounded
@@ -67,10 +72,14 @@ static inline u64 ll_sk_end_time(struct sock *sk) 
	return ((u64)ACCESS_ONCE(sk->sk_ll_usec) << 10) + ll_sched_clock();

}



/* in poll/select we use the global sysctl_net_ll_poll value */

/* in poll/select we use the global sysctl_net_ll_poll value

 * only call sched_clock() if enabled

 */

static inline u64 ll_end_time(void)

{

	return ((u64)ACCESS_ONCE(sysctl_net_ll_poll) << 10) + ll_sched_clock();

	u64 end_time = ACCESS_ONCE(sysctl_net_ll_poll);



	return end_time ? (end_time << 10) + ll_sched_clock() : 0;

}



static inline bool sk_valid_ll(struct sock *sk)
@@ -141,6 +150,10 @@ static inline void sk_mark_ll(struct sock *sk, struct sk_buff *skb) 
}



#else /* CONFIG_NET_LL_RX_POLL */

static inline unsigned long ll_get_flag(void)

{

	return 0;

}



static inline u64 sk_ll_end_time(struct sock *sk)

{