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| author |   Peter Zijlstra <peterz@infradead.org> | 2016-07-14 20:08:46 +0200 |
|---|---|---|
| committer |   Ingo Molnar <mingo@kernel.org> | 2016-08-10 14:34:01 +0200 |
| commit | 80127a39681bd68c959f0953f84a830cbd7c3b1c (patch) | |
| tree | 223bcc2a5cbec5c0873f8fae85a98797f94e6c56 /kernel/rcu | |
| parent | locking/pvstat: Separate wait_again and spurious wakeup stats (diff) | |
| download | wireguard-linux-80127a39681bd68c959f0953f84a830cbd7c3b1c.tar.xz wireguard-linux-80127a39681bd68c959f0953f84a830cbd7c3b1c.zip | |
locking/percpu-rwsem: Optimize readers and reduce global impact
Currently the percpu-rwsem switches to (global) atomic ops while a
writer is waiting; which could be quite a while and slows down
releasing the readers.
This patch cures this problem by ordering the reader-state vs
reader-count (see the comments in __percpu_down_read() and
percpu_down_write()). This changes a global atomic op into a full
memory barrier, which doesn't have the global cacheline contention.
This also enables using the percpu-rwsem with rcu_sync disabled in order
to bias the implementation differently, reducing the writer latency by
adding some cost to readers.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Paul McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
[ Fixed modular build. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel/rcu')
| -rw-r--r-- | kernel/rcu/sync.c | 2 |
1 files changed, 2 insertions, 0 deletions
diff --git a/kernel/rcu/sync.c b/kernel/rcu/sync.c index be922c9f3d37..198473d90f81 100644 --- a/kernel/rcu/sync.c +++ b/kernel/rcu/sync.c @@ -68,6 +68,8 @@ void rcu_sync_lockdep_assert(struct rcu_sync *rsp) RCU_LOCKDEP_WARN(!gp_ops[rsp->gp_type].held(), "suspicious rcu_sync_is_idle() usage"); } + +EXPORT_SYMBOL_GPL(rcu_sync_lockdep_assert); #endif /** |