From: Patrick Bellasi <patrick.bellasi@arm.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org,
linux-api@vger.kernel.org, Ingo Molnar <mingo@redhat.com>,
Tejun Heo <tj@kernel.org>,
"Rafael J . Wysocki" <rafael.j.wysocki@intel.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
Viresh Kumar <viresh.kumar@linaro.org>,
Paul Turner <pjt@google.com>,
Quentin Perret <quentin.perret@arm.com>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Morten Rasmussen <morten.rasmussen@arm.com>,
Juri Lelli <juri.lelli@redhat.com>, Todd Kjos <tkjos@google.com>,
Joel Fernandes <joelaf@google.com>,
Steve Muckle <smuckle@google.com>,
Suren Baghdasaryan <surenb@google.com>
Subject: Re: [PATCH v8 04/16] sched/core: uclamp: Add system default clamps
Date: Thu, 9 May 2019 14:04:44 +0100 [thread overview]
Message-ID: <20190509130444.4yawtbpjx2y7pp7g@e110439-lin> (raw)
In-Reply-To: <20190509115307.GS2623@hirez.programming.kicks-ass.net>
On 09-May 13:53, Peter Zijlstra wrote:
> On Thu, May 09, 2019 at 10:10:57AM +0100, Patrick Bellasi wrote:
> > On 08-May 21:15, Peter Zijlstra wrote:
> > > On Wed, May 08, 2019 at 09:07:33PM +0200, Peter Zijlstra wrote:
> > > > On Tue, Apr 02, 2019 at 11:41:40AM +0100, Patrick Bellasi wrote:
> > > > > +static inline struct uclamp_se
> > > > > +uclamp_eff_get(struct task_struct *p, unsigned int clamp_id)
> > > > > +{
> > > > > + struct uclamp_se uc_req = p->uclamp_req[clamp_id];
> > > > > + struct uclamp_se uc_max = uclamp_default[clamp_id];
> > > > > +
> > > > > + /* System default restrictions always apply */
> > > > > + if (unlikely(uc_req.value > uc_max.value))
> > > > > + return uc_max;
> > > > > +
> > > > > + return uc_req;
> > > > > +}
> > > > > +
> > > > > +static inline unsigned int
> > > > > +uclamp_eff_bucket_id(struct task_struct *p, unsigned int clamp_id)
> > > > > +{
> > > > > + struct uclamp_se uc_eff;
> > > > > +
> > > > > + /* Task currently refcounted: use back-annotated (effective) bucket */
> > > > > + if (p->uclamp[clamp_id].active)
> > > > > + return p->uclamp[clamp_id].bucket_id;
> > > > > +
> > > > > + uc_eff = uclamp_eff_get(p, clamp_id);
> > > > > +
> > > > > + return uc_eff.bucket_id;
> > > > > +}
> > > > > +
> > > > > +unsigned int uclamp_eff_value(struct task_struct *p, unsigned int clamp_id)
> > > > > +{
> > > > > + struct uclamp_se uc_eff;
> > > > > +
> > > > > + /* Task currently refcounted: use back-annotated (effective) value */
> > > > > + if (p->uclamp[clamp_id].active)
> > > > > + return p->uclamp[clamp_id].value;
> > > > > +
> > > > > + uc_eff = uclamp_eff_get(p, clamp_id);
> > > > > +
> > > > > + return uc_eff.value;
> > > > > +}
> > > >
> > > > This is 'wrong' because:
> > > >
> > > > uclamp_eff_value(p,id) := uclamp_eff(p,id).value
> > >
> > > Clearly I means to say the above does not hold with the given
> > > implementation, while the naming would suggest it does.
> >
> > Not sure to completely get your point...
>
> the point is that uclamp_eff_get() doesn't do the back annotate thing
> and therefore returns something entirely different from
> uclamp_eff_{bucket_id,value}(), where the naming would suggest it in
> fact returns the same thing.
>
> > > > Which seems to suggest the uclamp_eff_*() functions want another name.
> >
> > That function returns the effective value of a task, which is either:
> > 1. the back annotated value for a RUNNABLE task
> > or
> > 2. the aggregation of task-specific, system-default and cgroup values
> > for a non RUNNABLE task.
>
> Right, but uclamp_eff_get() doesn't do 1, while the other two do do it.
> And that is confusing.
I see, right.
> > > > Also, suppose the above would be true; does GCC really generate better
> > > > code for the LHS compared to the RHS?
> >
> > It generate "sane" code which implements the above logic and allows
> > to know that whenever we call uclamp_eff_value(p,id) we get the most
> > updated effective value for a task, independently from its {!}RUNNABLE
> > state.
> >
> > I would keep the function but, since Suren also complained also about
> > the name... perhaps I should come up with a better name? Proposals?
>
> Right, so they should move to the patch where they're needed, but I was
Yes, I'll move _value() to 10/16:
sched/core: uclamp: Add uclamp_util_with()
where we actually need to access the clamp value and...
> wondering why you'd not written something like:
>
> static inline
> struct uclamp_se uclamp_active(struct task_struct *p, unsigned int clamp_id)
> {
> if (p->uclamp[clamp_id].active)
> return p->uclamp[clamp_id];
>
> return uclamp_eff(p, clamp_id);
> }
>
> And then used:
>
> uclamp_active(p, id).{value,bucket_id}
>
> - OR -
>
> have uclamp_eff() include the active thing, afaict the callsite in
> uclamp_rq_inc_id() guarantees !active.
>
> In any case, I'm thinking the foo().member notation saves us from having
> to have two almost identical functions and the 'inline' part should get
> GCC to generate sane code.
... look into this approach, seems reasonable and actually better to read.
Thanks
--
#include <best/regards.h>
Patrick Bellasi
next prev parent reply other threads:[~2019-05-09 13:04 UTC|newest]
Thread overview: 50+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-04-02 10:41 [PATCH v8 00/16] Add utilization clamping support Patrick Bellasi
2019-04-02 10:41 ` [PATCH v8 01/16] sched/core: uclamp: Add CPU's clamp buckets refcounting Patrick Bellasi
2019-04-06 23:51 ` Suren Baghdasaryan
2019-04-08 11:49 ` Patrick Bellasi
2019-04-02 10:41 ` [PATCH v8 02/16] sched/core: Add bucket local max tracking Patrick Bellasi
2019-04-15 14:51 ` Patrick Bellasi
2019-04-02 10:41 ` [PATCH v8 03/16] sched/core: uclamp: Enforce last task's UCLAMP_MAX Patrick Bellasi
2019-04-17 20:36 ` Suren Baghdasaryan
2019-05-07 10:10 ` Patrick Bellasi
2019-04-02 10:41 ` [PATCH v8 04/16] sched/core: uclamp: Add system default clamps Patrick Bellasi
2019-04-18 0:51 ` Suren Baghdasaryan
2019-05-07 10:38 ` Patrick Bellasi
2019-05-08 18:42 ` Peter Zijlstra
2019-05-09 8:43 ` Patrick Bellasi
2019-05-08 19:00 ` Peter Zijlstra
2019-05-09 8:45 ` Patrick Bellasi
2019-05-08 19:07 ` Peter Zijlstra
2019-05-08 19:15 ` Peter Zijlstra
2019-05-09 9:10 ` Patrick Bellasi
2019-05-09 11:53 ` Peter Zijlstra
2019-05-09 13:04 ` Patrick Bellasi [this message]
2019-04-02 10:41 ` [PATCH v8 05/16] sched/core: Allow sched_setattr() to use the current policy Patrick Bellasi
2019-05-08 19:21 ` Peter Zijlstra
2019-05-09 9:18 ` Patrick Bellasi
2019-05-09 11:55 ` Peter Zijlstra
2019-05-09 14:59 ` Patrick Bellasi
2019-04-02 10:41 ` [PATCH v8 06/16] sched/core: uclamp: Extend sched_setattr() to support utilization clamping Patrick Bellasi
2019-04-17 22:26 ` Suren Baghdasaryan
2019-05-07 11:13 ` Patrick Bellasi
2019-05-08 19:44 ` Peter Zijlstra
2019-05-09 9:24 ` Patrick Bellasi
2019-05-08 19:41 ` Peter Zijlstra
2019-05-09 9:23 ` Patrick Bellasi
2019-04-02 10:41 ` [PATCH v8 07/16] sched/core: uclamp: Reset uclamp values on RESET_ON_FORK Patrick Bellasi
2019-04-02 10:41 ` [PATCH v8 08/16] sched/core: uclamp: Set default clamps for RT tasks Patrick Bellasi
2019-04-17 23:07 ` Suren Baghdasaryan
2019-05-07 11:25 ` Patrick Bellasi
2019-04-02 10:41 ` [PATCH v8 09/16] sched/cpufreq: uclamp: Add clamps for FAIR and " Patrick Bellasi
2019-04-02 10:41 ` [PATCH v8 10/16] sched/core: uclamp: Add uclamp_util_with() Patrick Bellasi
2019-04-02 10:41 ` [PATCH v8 11/16] sched/fair: uclamp: Add uclamp support to energy_compute() Patrick Bellasi
2019-05-09 12:51 ` Peter Zijlstra
2019-04-02 10:41 ` [PATCH v8 12/16] sched/core: uclamp: Extend CPU's cgroup controller Patrick Bellasi
2019-04-18 0:12 ` Suren Baghdasaryan
2019-05-07 11:42 ` Patrick Bellasi
2019-04-02 10:41 ` [PATCH v8 13/16] sched/core: uclamp: Propagate parent clamps Patrick Bellasi
2019-04-02 10:41 ` [PATCH v8 14/16] sched/core: uclamp: Propagate system defaults to root group Patrick Bellasi
2019-04-02 10:41 ` [PATCH v8 15/16] sched/core: uclamp: Use TG's clamps to restrict TASK's clamps Patrick Bellasi
2019-04-02 10:41 ` [PATCH v8 16/16] sched/core: uclamp: Update CPU's refcount on TG's clamp changes Patrick Bellasi
2019-05-09 13:02 ` [PATCH v8 00/16] Add utilization clamping support Peter Zijlstra
2019-05-09 13:09 ` Patrick Bellasi
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