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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 /include/linux/hardirq.h
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 'include/linux/hardirq.h')
-rw-r--r--include/linux/hardirq.h5
1 files changed, 5 insertions, 0 deletions
diff --git a/include/linux/hardirq.h b/include/linux/hardirq.h
index d5b387669da..e37a77cbd58 100644
--- a/include/linux/hardirq.h
+++ b/include/linux/hardirq.h
@@ -64,6 +64,8 @@
#define HARDIRQ_OFFSET (1UL << HARDIRQ_SHIFT)
#define NMI_OFFSET (1UL << NMI_SHIFT)
+#define SOFTIRQ_DISABLE_OFFSET (2 * SOFTIRQ_OFFSET)
+
#ifndef PREEMPT_ACTIVE
#define PREEMPT_ACTIVE_BITS 1
#define PREEMPT_ACTIVE_SHIFT (NMI_SHIFT + NMI_BITS)
@@ -82,10 +84,13 @@
/*
* Are we doing bottom half or hardware interrupt processing?
* Are we in a softirq context? Interrupt context?
+ * in_softirq - Are we currently processing softirq or have bh disabled?
+ * in_serving_softirq - Are we currently processing softirq?
*/
#define in_irq() (hardirq_count())
#define in_softirq() (softirq_count())
#define in_interrupt() (irq_count())
+#define in_serving_softirq() (softirq_count() & SOFTIRQ_OFFSET)
/*
* Are we in NMI context?