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sched/cputime: Support other fields on kcpustat_field()

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Provide support for user, nice, guest and guest_nice fields through
kcpustat_field().

Whether we account the delta to a nice or not nice field is decided on
top of the nice value snapshot taken at the time we call kcpustat_field().
If the nice value of the task has been changed since the last vtime
update, we may have inacurrate distribution of the nice VS unnice
cputime.

However this is considered as a minor issue compared to the proper fix
that would involve interrupting the target on nice updates, which is
undesired on nohz_full CPUs.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Wanpeng Li <wanpengli@tencent.com>
Cc: Yauheni Kaliuta <yauheni.kaliuta@redhat.com>
Link: https://lkml.kernel.org/r/20191121024430.19938-2-frederic@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Frederic Weisbecker 2019-11-21 03:44:25 +01:00 committed by Ingo Molnar
parent bef69dd878
commit 5a1c95580f
1 changed files with 43 additions and 11 deletions
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54
kernel/sched/cputime.c
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@ -912,11 +912,21 @@ void task_cputime(struct task_struct *t, u64 *utime, u64 *stime)
} while (read_seqcount_retry(&vtime->seqcount, seq));
}
static u64 kcpustat_user_vtime(struct vtime *vtime)
{
if (vtime->state == VTIME_USER)
return vtime->utime + vtime_delta(vtime);
else if (vtime->state == VTIME_GUEST)
return vtime->gtime + vtime_delta(vtime);
return 0;
}
static int kcpustat_field_vtime(u64 *cpustat,
struct vtime *vtime,
struct task_struct *tsk,
enum cpu_usage_stat usage,
int cpu, u64 *val)
{
struct vtime *vtime = &tsk->vtime;
unsigned int seq;
int err;
@ -946,9 +956,37 @@ static int kcpustat_field_vtime(u64 *cpustat,
*val = cpustat[usage];
if (vtime->state == VTIME_SYS)
*val += vtime->stime + vtime_delta(vtime);
/*
* Nice VS unnice cputime accounting may be inaccurate if
* the nice value has changed since the last vtime update.
* But proper fix would involve interrupting target on nice
* updates which is a no go on nohz_full (although the scheduler
* may still interrupt the target if rescheduling is needed...)
*/
switch (usage) {
case CPUTIME_SYSTEM:
if (vtime->state == VTIME_SYS)
*val += vtime->stime + vtime_delta(vtime);
break;
case CPUTIME_USER:
if (task_nice(tsk) <= 0)
*val += kcpustat_user_vtime(vtime);
break;
case CPUTIME_NICE:
if (task_nice(tsk) > 0)
*val += kcpustat_user_vtime(vtime);
break;
case CPUTIME_GUEST:
if (vtime->state == VTIME_GUEST && task_nice(tsk) <= 0)
*val += vtime->gtime + vtime_delta(vtime);
break;
case CPUTIME_GUEST_NICE:
if (vtime->state == VTIME_GUEST && task_nice(tsk) > 0)
*val += vtime->gtime + vtime_delta(vtime);
break;
default:
break;
}
} while (read_seqcount_retry(&vtime->seqcount, seq));
return 0;
@ -965,15 +1003,10 @@ u64 kcpustat_field(struct kernel_cpustat *kcpustat,
if (!vtime_accounting_enabled_cpu(cpu))
return cpustat[usage];
/* Only support sys vtime for now */
if (usage != CPUTIME_SYSTEM)
return cpustat[usage];
rq = cpu_rq(cpu);
for (;;) {
struct task_struct *curr;
struct vtime *vtime;
rcu_read_lock();
curr = rcu_dereference(rq->curr);
@ -982,8 +1015,7 @@ u64 kcpustat_field(struct kernel_cpustat *kcpustat,
return cpustat[usage];
}
vtime = &curr->vtime;
err = kcpustat_field_vtime(cpustat, vtime, usage, cpu, &val);
err = kcpustat_field_vtime(cpustat, curr, usage, cpu, &val);
rcu_read_unlock();
if (!err)