Revision ab4562f4dd92c455f6b313717af5e7d72a55d7b4 authored by Sébastien Szymanski on 25 February 2020, 12:39:04 UTC, committed by Rob Herring on 02 March 2020, 22:24:50 UTC
APF6 Dev compatible is armadeus,imx6dl-apf6dev and not armadeus,imx6dl-apf6dldev. Fixes: 3d735471d066 ("dt-bindings: arm: Document Armadeus SoM and Dev boards devicetree binding") Signed-off-by: Sébastien Szymanski <sebastien.szymanski@armadeus.com> Signed-off-by: Rob Herring <robh@kernel.org>
1 parent 51a21e0
percpu-rw-semaphore.txt
====================
Percpu rw semaphores
====================
Percpu rw semaphores is a new read-write semaphore design that is
optimized for locking for reading.
The problem with traditional read-write semaphores is that when multiple
cores take the lock for reading, the cache line containing the semaphore
is bouncing between L1 caches of the cores, causing performance
degradation.
Locking for reading is very fast, it uses RCU and it avoids any atomic
instruction in the lock and unlock path. On the other hand, locking for
writing is very expensive, it calls synchronize_rcu() that can take
hundreds of milliseconds.
The lock is declared with "struct percpu_rw_semaphore" type.
The lock is initialized percpu_init_rwsem, it returns 0 on success and
-ENOMEM on allocation failure.
The lock must be freed with percpu_free_rwsem to avoid memory leak.
The lock is locked for read with percpu_down_read, percpu_up_read and
for write with percpu_down_write, percpu_up_write.
The idea of using RCU for optimized rw-lock was introduced by
Eric Dumazet <eric.dumazet@gmail.com>.
The code was written by Mikulas Patocka <mpatocka@redhat.com>
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