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net: avoid calling sched_clock when LLS is off

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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: Andi Kleen <andi@firstfloor.org>
Signed-off-by: Eliezer Tamir <eliezer.tamir@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eliezer Tamir 2013-06-28 15:59:35 +03:00 • committed by David S. Miller
parent ad6276e0fe
commit 91e2fd3378
2 changed files with 22 additions and 6 deletions
Download patch file Download diff file Expand all files Collapse all files

11
fs/select.c
View file

@ -402,7 +402,7 @@ int do_select(int n, fd_set_bits *fds, struct timespec *end_time)
poll_table *wait; poll_table *wait;
int retval, i, timed_out = 0; int retval, i, timed_out = 0;
unsigned long slack = 0; unsigned long slack = 0;
unsigned int ll_flag = POLL_LL; unsigned int ll_flag = ll_get_flag();
u64 ll_time = ll_end_time(); u64 ll_time = ll_end_time();
rcu_read_lock(); rcu_read_lock();
@ -497,7 +497,8 @@ int do_select(int n, fd_set_bits *fds, struct timespec *end_time)
break; 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; continue;
/* /*
@ -768,7 +769,7 @@ static int do_poll(unsigned int nfds, struct poll_list *list,
ktime_t expire, *to = NULL; ktime_t expire, *to = NULL;
int timed_out = 0, count = 0; int timed_out = 0, count = 0;
unsigned long slack = 0; unsigned long slack = 0;
unsigned int ll_flag = POLL_LL; unsigned int ll_flag = ll_get_flag();
u64 ll_time = ll_end_time(); u64 ll_time = ll_end_time();
/* Optimise the no-wait case */ /* Optimise the no-wait case */
@ -817,8 +818,10 @@ static int do_poll(unsigned int nfds, struct poll_list *list,
if (count || timed_out) if (count || timed_out)
break; 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; continue;
/* /*
* If this is the first loop and we have a timeout * If this is the first loop and we have a timeout
* given, then we convert to ktime_t and set the to * given, then we convert to ktime_t and set the to

17
include/net/ll_poll.h
View file

@ -37,6 +37,11 @@ extern unsigned int sysctl_net_ll_poll __read_mostly;
#define LL_FLUSH_FAILED -1 #define LL_FLUSH_FAILED -1
#define LL_FLUSH_BUSY -2 #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 /* a wrapper to make debug_smp_processor_id() happy
* we can use sched_clock() because we don't care much about precision * we can use sched_clock() because we don't care much about precision
* we only care that the average is bounded * 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(); 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) 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) 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 */ #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) static inline u64 sk_ll_end_time(struct sock *sk)
{ {