Messages in this thread |  | | Date | Sun, 15 Nov 2020 13:05:21 +0800 | From | Yun Hsiang <> | Subject | Re: [PATCH v2] sched/uclamp: Allow to reset a task uclamp constraint value |
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Hi Dietmar, On Fri, Nov 13, 2020 at 12:34:54PM +0100, Dietmar Eggemann wrote: > In case the user wants to stop controlling a uclamp constraint value > for a task, use the magic value -1 in sched_util_{min,max} with the > appropriate sched_flags (SCHED_FLAG_UTIL_CLAMP_{MIN,MAX}) to indicate > the reset. > > The advantage over the 'additional flag' approach (i.e. introducing > SCHED_FLAG_UTIL_CLAMP_RESET) is that no additional flag has to be > exported via uapi. This avoids the need to document how this new flag > has be used in conjunction with the existing uclamp related flags. > > The following subtle issue is fixed as well. When a uclamp constraint > value is set on a !user_defined uclamp_se it is currently first reset > and then set. > Fix this by AND'ing !user_defined with !SCHED_FLAG_UTIL_CLAMP which > stands for the 'sched class change' case. > The related condition 'if (uc_se->user_defined)' moved from > __setscheduler_uclamp() into uclamp_reset().
I think this is great, thanks! Reviewed-by: Yun Hsiang <hsiang023167@gmail.com>
> > Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com> > --- > > v1 [1] -> v2: > > 1) Removed struct sched_attr (UAPI) change. > > 2) Use single branch range check in uclamp_validate(). > > [1] https://lkml.kernel.org/r/f3b59aad-3d5d-039b-205d-024308b609a1@arm.com > > include/uapi/linux/sched/types.h | 2 + > kernel/sched/core.c | 70 +++++++++++++++++++++++--------- > 2 files changed, 53 insertions(+), 19 deletions(-) > > diff --git a/include/uapi/linux/sched/types.h b/include/uapi/linux/sched/types.h > index c852153ddb0d..f2c4589d4dbf 100644 > --- a/include/uapi/linux/sched/types.h > +++ b/include/uapi/linux/sched/types.h > @@ -96,6 +96,8 @@ struct sched_param { > * on a CPU with a capacity big enough to fit the specified value. > * A task with a max utilization value smaller than 1024 is more likely > * scheduled on a CPU with no more capacity than the specified value. > + * > + * A task utilization boundary can be reset by setting the attribute to -1. > */ > struct sched_attr { > __u32 size; > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 3dc415f58bd7..a4805747b304 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -1413,17 +1413,24 @@ int sysctl_sched_uclamp_handler(struct ctl_table *table, int write, > static int uclamp_validate(struct task_struct *p, > const struct sched_attr *attr) > { > - unsigned int lower_bound = p->uclamp_req[UCLAMP_MIN].value; > - unsigned int upper_bound = p->uclamp_req[UCLAMP_MAX].value; > + int util_min = p->uclamp_req[UCLAMP_MIN].value; > + int util_max = p->uclamp_req[UCLAMP_MAX].value; > > - if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MIN) > - lower_bound = attr->sched_util_min; > - if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MAX) > - upper_bound = attr->sched_util_max; > + if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MIN) { > + util_min = attr->sched_util_min; > > - if (lower_bound > upper_bound) > - return -EINVAL; > - if (upper_bound > SCHED_CAPACITY_SCALE) > + if (util_min + 1 > SCHED_CAPACITY_SCALE + 1) > + return -EINVAL; > + } > + > + if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MAX) { > + util_max = attr->sched_util_max; > + > + if (util_max + 1 > SCHED_CAPACITY_SCALE + 1) > + return -EINVAL; > + } > + > + if (util_min != -1 && util_max != -1 && util_min > util_max) > return -EINVAL; > > /* > @@ -1438,20 +1445,41 @@ static int uclamp_validate(struct task_struct *p, > return 0; > } > > +static bool uclamp_reset(const struct sched_attr *attr, > + enum uclamp_id clamp_id, > + struct uclamp_se *uc_se) > +{ > + /* Reset on sched class change for a non user-defined clamp value. */ > + if (likely(!(attr->sched_flags & SCHED_FLAG_UTIL_CLAMP)) && > + !uc_se->user_defined) > + return true; > + > + /* Reset on sched_util_{min,max} == -1. */ > + if (clamp_id == UCLAMP_MIN && > + attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MIN && > + attr->sched_util_min == -1) { > + return true; > + } > + > + if (clamp_id == UCLAMP_MAX && > + attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MAX && > + attr->sched_util_max == -1) { > + return true; > + } > + > + return false; > +} > + > static void __setscheduler_uclamp(struct task_struct *p, > const struct sched_attr *attr) > { > enum uclamp_id clamp_id; > > - /* > - * On scheduling class change, reset to default clamps for tasks > - * without a task-specific value. > - */ > for_each_clamp_id(clamp_id) { > struct uclamp_se *uc_se = &p->uclamp_req[clamp_id]; > + unsigned int value; > > - /* Keep using defined clamps across class changes */ > - if (uc_se->user_defined) > + if (!uclamp_reset(attr, clamp_id, uc_se)) > continue; > > /* > @@ -1459,21 +1487,25 @@ static void __setscheduler_uclamp(struct task_struct *p, > * at runtime. > */ > if (unlikely(rt_task(p) && clamp_id == UCLAMP_MIN)) > - __uclamp_update_util_min_rt_default(p); > + value = sysctl_sched_uclamp_util_min_rt_default; > else > - uclamp_se_set(uc_se, uclamp_none(clamp_id), false); > + value = uclamp_none(clamp_id); > + > + uclamp_se_set(uc_se, value, false); > > } > > if (likely(!(attr->sched_flags & SCHED_FLAG_UTIL_CLAMP))) > return; > > - if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MIN) { > + if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MIN && > + attr->sched_util_min != -1) { > uclamp_se_set(&p->uclamp_req[UCLAMP_MIN], > attr->sched_util_min, true); > } > > - if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MAX) { > + if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MAX && > + attr->sched_util_max != -1) { > uclamp_se_set(&p->uclamp_req[UCLAMP_MAX], > attr->sched_util_max, true); > } > -- > 2.17.1 >
Best Regards, Yun
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