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locking/percpu-rwsem: Make use of the rcu_sync infrastructure

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Currently down_write/up_write calls synchronize_sched_expedited()
twice, which is evil.  Change this code to rely on rcu-sync primitives.
This avoids the _expedited "big hammer", and this can be faster in
the contended case or even in the case when a single thread does
down_write/up_write in a loop.

Of course, a single down_write() will take more time, but otoh it
will be much more friendly to the whole system.

To simplify the review this patch doesn't update the comments, fixed
by the next change.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
This commit is contained in:
Oleg Nesterov 2015-08-21 19:42:57 +02:00 • committed by Paul E. McKenney
parent 95b19f684c
commit 001dac627f
2 changed files with 9 additions and 12 deletions
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3
include/linux/percpu-rwsem.h
View file

@ -5,11 +5,12 @@
#include <linux/rwsem.h>
#include <linux/percpu.h>
#include <linux/wait.h>
#include <linux/rcu_sync.h>
#include <linux/lockdep.h>
struct percpu_rw_semaphore {
struct rcu_sync rss;
unsigned int __percpu *fast_read_ctr;
atomic_t write_ctr;
struct rw_semaphore rw_sem;
atomic_t slow_read_ctr;
wait_queue_head_t write_waitq;