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SubjectRe: [PATCH] sched/cpuacct: Fix charge cpuacct.usage_sys incorrently.
On Thu, 16 Apr 2020 11:35:02 -0400
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.

Perhaps you want:

regs = get_irqs_regs();
if (!regs)
regs = task_pt_regs(tsk);

?

-- Steve

>
> >
> > if (regs && user_mode(regs))
> > index = CPUACCT_STAT_USER;
>

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