39 lines
1.5 KiB
Diff
39 lines
1.5 KiB
Diff
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From 7b5447090b8fbb80a85320c880934f35acbf68a7 Mon Sep 17 00:00:00 2001
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From: Arjan van de Ven <arjan@linux.intel.com>
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Date: Wed, 11 Feb 2015 16:25:16 -0600
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Subject: [PATCH 03/22] sysrq: skip synchronize_rcu() if there is no old op
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synchronize_rcu() is expensive. Currently it is called as part of the sysrq
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registration/unregistration, which happens during boot several times.
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Now, the reason for the synchronize_rcu() is to allow an old registered
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operation to expire properly... which is pointless if the old operation
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is NULL...
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So we can save the common case of the old operation being NULL a lot of time
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by just checking for non-NULL prior to the synchronize_rcu()
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Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
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Signed-off-by: Miguel Bernal Marin <miguel.bernal.marin@linux.intel.com>
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---
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drivers/tty/sysrq.c | 4 +++-
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1 file changed, 3 insertions(+), 1 deletion(-)
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diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c
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index 701c085b..c60c7ba5 100644
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--- a/drivers/tty/sysrq.c
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+++ b/drivers/tty/sysrq.c
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@@ -1065,8 +1065,10 @@ static int __sysrq_swap_key_ops(int key, struct sysrq_key_op *insert_op_p,
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* A concurrent __handle_sysrq either got the old op or the new op.
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* Wait for it to go away before returning, so the code for an old
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* op is not freed (eg. on module unload) while it is in use.
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+ * This is only relevant if the old op is not NULL of course.
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*/
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- synchronize_rcu();
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+ if (remove_op_p)
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+ synchronize_rcu();
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return retval;
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}
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--
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2.11.0
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