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| author | Venkatesh Pallipadi <venki@google.com> | 2010-10-04 17:03:16 -0700 |
|---|---|---|
| committer | Ingo Molnar <mingo@elte.hu> | 2010-10-18 20:52:20 +0200 |
| commit | 75e1056f5c57050415b64cb761a3acc35d91f013 (patch) | |
| tree | e7cd483e38f9bf9131a3b212301a009890b8de49 /include/linux/sched.h | |
| parent | 75dd321d79d495a0ee579e6249ebc38ddbb2667f (diff) | |
| download | lwn-75e1056f5c57050415b64cb761a3acc35d91f013.tar.gz lwn-75e1056f5c57050415b64cb761a3acc35d91f013.zip | |
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/sched.h')
| -rw-r--r-- | include/linux/sched.h | 6 |
1 files changed, 3 insertions, 3 deletions
diff --git a/include/linux/sched.h b/include/linux/sched.h index cdf56693ecbf..8744e50cb083 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -2366,9 +2366,9 @@ extern int __cond_resched_lock(spinlock_t *lock); extern int __cond_resched_softirq(void); -#define cond_resched_softirq() ({ \ - __might_sleep(__FILE__, __LINE__, SOFTIRQ_OFFSET); \ - __cond_resched_softirq(); \ +#define cond_resched_softirq() ({ \ + __might_sleep(__FILE__, __LINE__, SOFTIRQ_DISABLE_OFFSET); \ + __cond_resched_softirq(); \ }) /* |