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authorPeter Zijlstra <peterz@infradead.org>2016-07-14 20:08:46 +0200
committerIngo Molnar <mingo@kernel.org>2016-08-10 14:34:01 +0200
commit80127a39681bd68c959f0953f84a830cbd7c3b1c (patch)
tree223bcc2a5cbec5c0873f8fae85a98797f94e6c56 /fs/fat/misc.c
parentlocking/pvstat: Separate wait_again and spurious wakeup stats (diff)
downloadlinux-80127a39681bd68c959f0953f84a830cbd7c3b1c.tar.xz
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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>
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