From: Paul E. McKenney Date: Thu, 15 Apr 2010 00:39:26 +0000 (-0700) Subject: rcu: reduce the number of spurious RCU_SOFTIRQ invocations X-Git-Tag: v2.6.35-rc1~524^2~7 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=d21670acab9fcb4bc74a40b68a6941059234c55c;p=pandora-kernel.git 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 Signed-off-by: Paul E. McKenney --- Reading git-diff-tree failed