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authorVenkatesh Pallipadi <venki@google.com>2010-10-04 17:03:16 -0700
committerIngo Molnar <mingo@elte.hu>2010-10-18 20:52:20 +0200
commit75e1056f5c57050415b64cb761a3acc35d91f013 (patch)
treee7cd483e38f9bf9131a3b212301a009890b8de49 /kernel/sched.c
parent75dd321d79d495a0ee579e6249ebc38ddbb2667f (diff)
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sched: Fix softirq time accounting
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>
Diffstat (limited to 'kernel/sched.c')
-rw-r--r--kernel/sched.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/kernel/sched.c b/kernel/sched.c
index 771b518e5f1..089be8adb07 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -3422,7 +3422,7 @@ void account_system_time(struct task_struct *p, int hardirq_offset,
tmp = cputime_to_cputime64(cputime);
if (hardirq_count() - hardirq_offset)
cpustat->irq = cputime64_add(cpustat->irq, tmp);
- else if (softirq_count())
+ else if (in_serving_softirq())
cpustat->softirq = cputime64_add(cpustat->softirq, tmp);
else
cpustat->system = cputime64_add(cpustat->system, tmp);