Messages in this thread Patch in this message | | | From | Patrick Bellasi <> | Subject | Re: [RFC PATCH 1/9] sched,cgroup: Add interface for latency-nice | Date | Thu, 05 Sep 2019 11:05:18 +0100 |
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We already commented on adding the cgroup API after the per-task API.
However, for the cgroup bits will be super important to have
[ +tejun ]
in CC since here we are at discussing the idea to add a new cpu controller's attribute.
There are opinions about which kind of attributes can be added to cgroups and I'm sure a "latency-nice" attribute will generate an interesting discussion. :)
LPC is coming up, perhaps we can get the chance to have a chat with Tejun about the manoeuvring space in this area.
On Fri, Aug 30, 2019 at 18:49:36 +0100, subhra mazumdar wrote...
> Add Cgroup interface for latency-nice. Each CPU Cgroup adds a new file > "latency-nice" which is shared by all the threads in that Cgroup. > > Signed-off-by: subhra mazumdar <subhra.mazumdar@oracle.com> > --- > include/linux/sched.h | 1 + > kernel/sched/core.c | 40 ++++++++++++++++++++++++++++++++++++++++ > kernel/sched/fair.c | 1 + > kernel/sched/sched.h | 8 ++++++++ > 4 files changed, 50 insertions(+) > > diff --git a/include/linux/sched.h b/include/linux/sched.h > index 1183741..b4a79c3 100644 > --- a/include/linux/sched.h > +++ b/include/linux/sched.h > @@ -631,6 +631,7 @@ struct task_struct { > int static_prio; > int normal_prio; > unsigned int rt_priority; > + u64 latency_nice;
I guess we can save some bit here... or, if we are very brave, maybe we can explore the possibility to pack all prios into a single u64?
( ( (tomatoes target here) ) )
> const struct sched_class *sched_class; > struct sched_entity se; > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 874c427..47969bc 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -5976,6 +5976,7 @@ void __init sched_init(void) > init_dl_rq(&rq->dl); > #ifdef CONFIG_FAIR_GROUP_SCHED > root_task_group.shares = ROOT_TASK_GROUP_LOAD; > + root_task_group.latency_nice = LATENCY_NICE_DEFAULT; > INIT_LIST_HEAD(&rq->leaf_cfs_rq_list); > rq->tmp_alone_branch = &rq->leaf_cfs_rq_list; > /* > @@ -6345,6 +6346,7 @@ static void sched_change_group(struct task_struct *tsk, int type) > */ > tg = container_of(task_css_check(tsk, cpu_cgrp_id, true), > struct task_group, css); > + tsk->latency_nice = tg->latency_nice; > tg = autogroup_task_group(tsk, tg); > tsk->sched_task_group = tg; > > @@ -6812,6 +6814,34 @@ static u64 cpu_rt_period_read_uint(struct cgroup_subsys_state *css, > } > #endif /* CONFIG_RT_GROUP_SCHED */ > > +static u64 cpu_latency_nice_read_u64(struct cgroup_subsys_state *css, > + struct cftype *cft) > +{ > + struct task_group *tg = css_tg(css); > + > + return tg->latency_nice; > +} > + > +static int cpu_latency_nice_write_u64(struct cgroup_subsys_state *css, > + struct cftype *cft, u64 latency_nice) > +{ > + struct task_group *tg = css_tg(css); > + struct css_task_iter it; > + struct task_struct *p; > + > + if (latency_nice < LATENCY_NICE_MIN || latency_nice > LATENCY_NICE_MAX) > + return -ERANGE; > + > + tg->latency_nice = latency_nice; > + > + css_task_iter_start(css, 0, &it); > + while ((p = css_task_iter_next(&it))) > + p->latency_nice = latency_nice;
Once (and if) the cgroup API is added we can avoid this (potentially massive) "update on write" in favour of an "on demand composition at wakeup-time".
We don't care about updating the latency-nice of NON RUNNABLE tasks, do we?
AFAIK, we need that value only (or mostly) at wakeup time. Thus, when a task wakeup up we can easily compose (and eventually cache) it's current latency-nice value by considering, in priority order:
- the system wide upper-bound - the task group restriction - the task specific relaxation
Something similar to what we already do for uclamp composition with this patch currently in tip/sched/core:
commit 3eac870a3247 ("sched/uclamp: Use TG's clamps to restrict TASK's clamps")
> + css_task_iter_end(&it); > + > + return 0; > +} > + > static struct cftype cpu_legacy_files[] = { > #ifdef CONFIG_FAIR_GROUP_SCHED > { > @@ -6848,6 +6878,11 @@ static struct cftype cpu_legacy_files[] = { > .write_u64 = cpu_rt_period_write_uint, > }, > #endif > + { > + .name = "latency-nice", > + .read_u64 = cpu_latency_nice_read_u64, > + .write_u64 = cpu_latency_nice_write_u64, > + }, > { } /* Terminate */ > }; > > @@ -7015,6 +7050,11 @@ static struct cftype cpu_files[] = { > .write = cpu_max_write, > }, > #endif > + { > + .name = "latency-nice", > + .read_u64 = cpu_latency_nice_read_u64, > + .write_u64 = cpu_latency_nice_write_u64, > + }, > { } /* terminate */ > }; > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index f35930f..b08d00c 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -10479,6 +10479,7 @@ int alloc_fair_sched_group(struct task_group *tg, struct task_group *parent) > goto err; > > tg->shares = NICE_0_LOAD; > + tg->latency_nice = LATENCY_NICE_DEFAULT; ^^^^^^^^^^^^^^^^^^^^ Maybe better NICE_0_LATENCY to be more consistent?
> init_cfs_bandwidth(tg_cfs_bandwidth(tg)); > > diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h > index b52ed1a..365c928 100644 > --- a/kernel/sched/sched.h > +++ b/kernel/sched/sched.h > @@ -143,6 +143,13 @@ static inline void cpu_load_update_active(struct rq *this_rq) { } > #define NICE_0_LOAD (1L << NICE_0_LOAD_SHIFT) > > /* > + * Latency-nice default value > + */ > +#define LATENCY_NICE_DEFAULT 5 > +#define LATENCY_NICE_MIN 1 > +#define LATENCY_NICE_MAX 100
Values 1 and 5 looks kind of arbitrary. For the range specifically, I already commented in this other message:
Message-ID: <87r24v2i14.fsf@arm.com> https://lore.kernel.org/lkml/87r24v2i14.fsf@arm.com/
> + > +/* > * Single value that decides SCHED_DEADLINE internal math precision. > * 10 -> just above 1us > * 9 -> just above 0.5us > @@ -362,6 +369,7 @@ struct cfs_bandwidth { > /* Task group related information */ > struct task_group { > struct cgroup_subsys_state css; > + u64 latency_nice; > > #ifdef CONFIG_FAIR_GROUP_SCHED > /* schedulable entities of this group on each CPU */
Best, Patrick
-- #include <best/regards.h>
Patrick Bellasi
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