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Date: Fri, 17 Apr 2020 11:07:29 +0800
From: Muchun Song <songmuchun@...edance.com>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: mingo@...hat.com, Peter Zijlstra <peterz@...radead.org>,
juri.lelli@...hat.com,
Vincent Guittot <vincent.guittot@...aro.org>,
dietmar.eggemann@....com, Benjamin Segall <bsegall@...gle.com>,
mgorman@...e.de, mingo@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [External] Re: [PATCH] sched/cpuacct: Fix charge
cpuacct.usage_sys incorrently.
On Thu, Apr 16, 2020 at 11:35 PM Steven Rostedt <rostedt@...dmis.org> wrote:
>
> On Thu, 16 Apr 2020 22:18:33 +0800
> Muchun Song <songmuchun@...edance.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@...edance.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@...gle.com) and Balbir Singh
> > * (balbir@...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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