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| author | Peter Zijlstra <peterz@infradead.org> | 2016-08-09 08:44:12 -0700 |
|---|---|---|
| committer | Amit Pundir <amit.pundir@linaro.org> | 2016-09-14 14:26:20 +0530 |
| commit | d4d74af4b871915fe926d2f267e311949e0bf4b4 (patch) | |
| tree | 0cbb310a4266932a2dbbd36a03b543fe5ded614c /kernel/fork.c | |
| parent | 0e806c83bca02211f6b2e3de31df085eb4cf3508 (diff) | |
RFC: FROMLIST: 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.
Mailing-list-URL: https://lkml.org/lkml/2016/8/9/181
Cc: Paul McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
[jstultz: Backported to 4.4]
Change-Id: I8ea04b4dca2ec36f1c2469eccafde1423490572f
Signed-off-by: John Stultz <john.stultz@linaro.org>
Diffstat (limited to 'kernel/fork.c')
0 files changed, 0 insertions, 0 deletions