Messages in this thread | | | Date | Tue, 24 Jul 2018 17:43:03 +0100 | From | Patrick Bellasi <> | Subject | Re: [PATCH v2 12/12] sched/core: uclamp: use percentage clamp values |
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On 21-Jul 21:04, Suren Baghdasaryan wrote: > On Mon, Jul 16, 2018 at 1:29 AM, Patrick Bellasi > <patrick.bellasi@arm.com> wrote:
[...]
> > +static inline unsigned int scale_from_percent(unsigned int pct) > > +{ > > + WARN_ON(pct > 100); > > + > > + return ((SCHED_FIXEDPOINT_SCALE * pct) / 100); > > +} > > + > > +static inline unsigned int scale_to_percent(unsigned int value) > > +{ > > + unsigned int rounding = 0; > > + > > + WARN_ON(value > SCHED_FIXEDPOINT_SCALE); > > + > > + /* Compensate rounding errors for: 0, 256, 512, 768, 1024 */ > > + if (likely((value & 0xFF) && ~(value & 0x700))) > > + rounding = 1; > > Hmm. I don't think ~(value & 0x700) will ever yield FALSE... What am I missing?
So, 0x700 is the topmost 3 bits sets (111 0000 0000) which different configuration corresponds to:
001 0000 0000 => 256 010 0000 0000 => 512 011 0000 0000 => 768 100 0000 0000 => 1024
Thus, if 0x700 matches then we have one of these values in input and for these cases we have to add a unit to the percentage value.
For the case (value == 0) we translate it into 0% thanks to the check on (value & 0xFF) to ensure rounding = 0.
Here is a small python snippet I've used to check the conversion of all the possible percentage values:
---8<--- values = range(0, 101) for pct in xrange(0, 101): util = int((1024 * pct) / 100) rounding = 1 if not ((util & 0xFF) and ~(util & 0x700)): print "Fixing util_to_perc({:3d} => {:4d})".format(pct, util) rounding = 0 pct2 = (rounding + ((100 * util) / 1024)) if pct2 in values: values.remove(pct2) if pct != pct2: print "Convertion failed for: {:3d} => {:4d} => {:3d}".format(pct, util, pct2) if values: print "ERROR: not all percentage values converted" ---8<---
-- #include <best/regards.h>
Patrick Bellasi
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