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| author | Simon Horman <horms@verge.net.au> | 2013-05-22 14:50:31 +0900 |
|---|---|---|
| committer | Maciej Wereski <m.wereski@partner.samsung.com> | 2014-12-29 09:31:34 +0100 |
| commit | d71cd852d88a36a25b0e8ad05a5f72f540bdd085 (patch) | |
| tree | 33e8a3a158c92fcb6375b8f36fe359c902c33f19 | |
| parent | 960e9f6d75ac7720fc7af5770369d67af6adb575 (diff) | |
| download | linux-3.10-d71cd852d88a36a25b0e8ad05a5f72f540bdd085.tar.gz linux-3.10-d71cd852d88a36a25b0e8ad05a5f72f540bdd085.tar.bz2 linux-3.10-d71cd852d88a36a25b0e8ad05a5f72f540bdd085.zip | |
sched: add cond_resched_rcu() helper
This is intended for use in loops which read data protected by RCU and may
have a large number of iterations. Such an example is dumping the list of
connections known to IPVS: ip_vs_conn_array() and ip_vs_conn_seq_next().
The benefits are for CONFIG_PREEMPT_RCU=y where we save CPU cycles
by moving rcu_read_lock and rcu_read_unlock out of large loops
but still allowing the current task to be preempted after every
loop iteration for the CONFIG_PREEMPT_RCU=n case.
The call to cond_resched() is not needed when CONFIG_PREEMPT_RCU=y.
Thanks to Paul E. McKenney for explaining this and for the
final version that checks the context with CONFIG_DEBUG_ATOMIC_SLEEP=y
for all possible configurations.
The function can be empty in the CONFIG_PREEMPT_RCU case,
rcu_read_lock and rcu_read_unlock are not needed in this case
because the task can be preempted on indication from scheduler.
Thanks to Peter Zijlstra for catching this and for his help
in trying a solution that changes __might_sleep.
Initial cond_resched_rcu_lock() function suggested by Eric Dumazet.
Tested-by: Julian Anastasov <ja@ssi.bg>
Signed-off-by: Julian Anastasov <ja@ssi.bg>
Signed-off-by: Simon Horman <horms@verge.net.au>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Change-Id: I5f36f86484198f9064725d424c3d91d5fac8e1d4
Origin: https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=f6f3c437d09e2f62533034e67bfb4385191e992c
Backported-by: Maciej Wereski <m.wereski@partner.samsung.com>
Signed-off-by: Maciej Wereski <m.wereski@partner.samsung.com>
| -rw-r--r-- | include/linux/sched.h | 9 |
1 files changed, 9 insertions, 0 deletions
diff --git a/include/linux/sched.h b/include/linux/sched.h index f87e9a8d364..e12df9e68e3 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -2462,6 +2462,15 @@ extern int __cond_resched_softirq(void); __cond_resched_softirq(); \ }) +static inline void cond_resched_rcu(void) +{ +#if defined(CONFIG_DEBUG_ATOMIC_SLEEP) || !defined(CONFIG_PREEMPT_RCU) + rcu_read_unlock(); + cond_resched(); + rcu_read_lock(); +#endif +} + /* * Does a critical section need to be broken due to another * task waiting?: (technically does not depend on CONFIG_PREEMPT, |