Messages in this thread | | | From | Muchun Song <> | Date | Fri, 17 Apr 2020 11:07:29 +0800 | Subject | Re: [External] Re: [PATCH] sched/cpuacct: Fix charge cpuacct.usage_sys incorrently. |
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On Thu, Apr 16, 2020 at 11:35 PM Steven Rostedt <rostedt@goodmis.org> wrote: > > On Thu, 16 Apr 2020 22:18:33 +0800 > Muchun Song <songmuchun@bytedance.com> wrote: > > > The user_mode(task_pt_regs(tsk)) always return true for > > user thread, and false for kernel thread. So it means that > > the cpuacct.usage_sys is the time that kernel thread uses > > not the time that thread uses in the kernel mode. We can > > use get_irq_regs() instead of task_pt_regs() to fix it. > > > > Signed-off-by: Muchun Song <songmuchun@bytedance.com> > > --- > > kernel/sched/cpuacct.c | 3 ++- > > 1 file changed, 2 insertions(+), 1 deletion(-) > > > > diff --git a/kernel/sched/cpuacct.c b/kernel/sched/cpuacct.c > > index 6448b0438ffb2..edfc62554648e 100644 > > --- a/kernel/sched/cpuacct.c > > +++ b/kernel/sched/cpuacct.c > > @@ -5,6 +5,7 @@ > > * Based on the work by Paul Menage (menage@google.com) and Balbir Singh > > * (balbir@in.ibm.com). > > */ > > +#include <asm/irq_regs.h> > > #include "sched.h" > > > > /* Time spent by the tasks of the CPU accounting group executing in ... */ > > @@ -339,7 +340,7 @@ void cpuacct_charge(struct task_struct *tsk, u64 cputime) > > { > > struct cpuacct *ca; > > int index = CPUACCT_STAT_SYSTEM; > > - struct pt_regs *regs = task_pt_regs(tsk); > > + struct pt_regs *regs = get_irq_regs(); > > But get_irq_regs() is only available from interrupt context. This will be > NULL most the time, whereas the original way will have regs existing for > the task. > > > > > if (regs && user_mode(regs)) > > index = CPUACCT_STAT_USER; > > To show this, I applied your patch then did the following: > > # echo 'p:cpuacct cpuacct_charge+0x36 regs=%ax' > /sys/kernel/tracing/kprobe_events > > Where I found that the test of 'regs' is %rax at offset 0x36. > > # trace-cmd start -p function -l cpuacct_charge -e kprobes > # trace-cmd show > # tracer: function > # > # entries-in-buffer/entries-written: 70664/70664 #P:8 > # > # _-----=> irqs-off > # / _----=> need-resched > # | / _---=> hardirq/softirq > # || / _--=> preempt-depth > # ||| / delay > # TASK-PID CPU# |||| TIMESTAMP FUNCTION > # | | | |||| | | > <...>-1720 [002] d..2 306.430302: cpuacct_charge <-update_curr > <...>-1720 [002] d..3 306.430306: cpuacct: (cpuacct_charge+0x36/0x1f0) regs=0x0 > <...>-1720 [002] dN.2 306.430321: cpuacct_charge <-update_curr > <...>-1720 [002] dN.3 306.430322: cpuacct: (cpuacct_charge+0x36/0x1f0) regs=0x0 > <...>-1720 [002] d..2 306.430355: cpuacct_charge <-update_curr > <...>-1720 [002] d..3 306.430357: cpuacct: (cpuacct_charge+0x36/0x1f0) regs=0x0 > bash-1652 [006] d.h2 306.430799: cpuacct_charge <-update_curr > bash-1652 [006] d.h3 306.430802: cpuacct: (cpuacct_charge+0x36/0x1f0) regs=0xffffaf34012abdd8 > <...>-199 [005] d.h2 306.430806: cpuacct_charge <-update_curr > <...>-199 [005] d.h3 306.430809: cpuacct: (cpuacct_charge+0x36/0x1f0) regs=0xffffaf3400347c38 > <...>-16 [001] d..2 306.430873: cpuacct_charge <-update_curr > <...>-16 [001] d..3 306.430875: cpuacct: (cpuacct_charge+0x36/0x1f0) regs=0x0 > <...>-199 [005] d..2 306.430936: cpuacct_charge <-update_curr > <...>-199 [005] d..3 306.430937: cpuacct: (cpuacct_charge+0x36/0x1f0) regs=0x0 > bash-1652 [006] d..2 306.430944: cpuacct_charge <-update_curr > bash-1652 [006] d..3 306.430946: cpuacct: (cpuacct_charge+0x36/0x1f0) regs=0x0 > sshd-1649 [000] d..2 306.430990: cpuacct_charge <-update_curr > sshd-1649 [000] d..3 306.430992: cpuacct: (cpuacct_charge+0x36/0x1f0) regs=0x0 > rcu_preempt-10 [006] d..2 306.432844: cpuacct_charge <-update_curr > rcu_preempt-10 [006] d..3 306.432846: cpuacct: (cpuacct_charge+0x36/0x1f0) regs=0x0 > rcu_preempt-10 [006] d..2 306.436848: cpuacct_charge <-update_curr > rcu_preempt-10 [006] d..3 306.436850: cpuacct: (cpuacct_charge+0x36/0x1f0) regs=0x0 > rcu_preempt-10 [006] d..2 306.440868: cpuacct_charge <-update_curr > rcu_preempt-10 [006] d..3 306.440871: cpuacct: (cpuacct_charge+0x36/0x1f0) regs=0x0 > rcu_preempt-10 [006] d..2 306.444867: cpuacct_charge <-update_curr > rcu_preempt-10 [006] d..3 306.444870: cpuacct: (cpuacct_charge+0x36/0x1f0) regs=0x0 > kworker/2:1-127 [002] d..2 306.446925: cpuacct_charge <-update_curr > kworker/2:1-127 [002] d..3 306.446928: cpuacct: (cpuacct_charge+0x36/0x1f0) regs=0x0 > rcu_preempt-10 [006] d..2 306.448868: cpuacct_charge <-update_curr > rcu_preempt-10 [006] d..3 306.448870: cpuacct: (cpuacct_charge+0x36/0x1f0) regs=0x0 > rcu_preempt-10 [006] d..2 306.452869: cpuacct_charge <-update_curr > rcu_preempt-10 [006] d..3 306.452872: cpuacct: (cpuacct_charge+0x36/0x1f0) regs=0x0 > > The only times regs has content is from the the interrupt handler (seen as > the 'h' in the status portion of the trace. > > -- Steve
Thanks for your test. You are right.
-- Yours, Muchun
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