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author | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2010-04-14 17:39:26 -0700 |
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committer | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2010-05-10 11:08:35 -0700 |
commit | d21670acab9fcb4bc74a40b68a6941059234c55c (patch) | |
tree | 6a4c054bc4dbadf0524b4e221889a8da558dbdaf /drivers/scsi/sr.c | |
parent | 4a90a0681cf6cd21cd444184302aa045156486b3 (diff) | |
download | op-kernel-dev-d21670acab9fcb4bc74a40b68a6941059234c55c.zip op-kernel-dev-d21670acab9fcb4bc74a40b68a6941059234c55c.tar.gz |
rcu: reduce the number of spurious RCU_SOFTIRQ invocations
Lai Jiangshan noted that up to 10% of the RCU_SOFTIRQ are spurious, and
traced this down to the fact that the current grace-period machinery
will uselessly raise RCU_SOFTIRQ when a given CPU needs to go through
a quiescent state, but has not yet done so. In this situation, there
might well be nothing that RCU_SOFTIRQ can do, and the overhead can be
worth worrying about in the ksoftirqd case. This patch therefore avoids
raising RCU_SOFTIRQ in this situation.
Changes since v1 (http://lkml.org/lkml/2010/3/30/122 from Lai Jiangshan):
o Omit the rcu_qs_pending() prechecks, as they aren't that
much less expensive than the quiescent-state checks.
o Merge with the set_need_resched() patch that reduces IPIs.
o Add the new n_rp_report_qs field to the rcu_pending tracing output.
o Update the tracing documentation accordingly.
Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Diffstat (limited to 'drivers/scsi/sr.c')
0 files changed, 0 insertions, 0 deletions