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authorVenkatesh Pallipadi <venki@google.com>2011-02-10 10:23:26 +0100
committerGreg Kroah-Hartman <gregkh@suse.de>2011-02-17 15:37:24 -0800
commit49c6f4a2ba104ce198c61445edbff78ce1508a65 (patch)
tree87db2d6d963ca83b7699e98b06a593697118548b /net
parent1d3d2371a682f9905153bf28cc21ee1d2184bb44 (diff)
sched: Fix softirq time accounting
Commit: 75e1056f5c57050415b64cb761a3acc35d91f013 upstream Peter Zijlstra found a bug in the way softirq time is accounted in VIRT_CPU_ACCOUNTING on this thread: http://lkml.indiana.edu/hypermail//linux/kernel/1009.2/01366.html The problem is, softirq processing uses local_bh_disable internally. There is no way, later in the flow, to differentiate between whether softirq is being processed or is it just that bh has been disabled. So, a hardirq when bh is disabled results in time being wrongly accounted as softirq. Looking at the code a bit more, the problem exists in !VIRT_CPU_ACCOUNTING as well. As account_system_time() in normal tick based accouting also uses softirq_count, which will be set even when not in softirq with bh disabled. Peter also suggested solution of using 2*SOFTIRQ_OFFSET as irq count for local_bh_{disable,enable} and using just SOFTIRQ_OFFSET while softirq processing. The patch below does that and adds API in_serving_softirq() which returns whether we are currently processing softirq or not. Also changes one of the usages of softirq_count in net/sched/cls_cgroup.c to in_serving_softirq. Looks like many usages of in_softirq really want in_serving_softirq. Those changes can be made individually on a case by case basis. Signed-off-by: Venkatesh Pallipadi <venki@google.com> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> LKML-Reference: <1286237003-12406-2-git-send-email-venki@google.com> Signed-off-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Mike Galbraith <efault@gmx.de> Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Diffstat (limited to 'net')
-rw-r--r--net/sched/cls_cgroup.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/net/sched/cls_cgroup.c b/net/sched/cls_cgroup.c
index e4877ca6727..f4f02313f96 100644
--- a/net/sched/cls_cgroup.c
+++ b/net/sched/cls_cgroup.c
@@ -110,7 +110,7 @@ static int cls_cgroup_classify(struct sk_buff *skb, struct tcf_proto *tp,
* calls by looking at the number of nested bh disable calls because
* softirqs always disables bh.
*/
- if (softirq_count() != SOFTIRQ_OFFSET)
+ if (in_serving_softirq())
return -1;
rcu_read_lock();