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
