Messages in this thread | | | Date | Mon, 8 Jul 2019 12:08:41 +0100 | From | Quentin Perret <> | Subject | Re: [PATCH v11 1/5] sched/core: uclamp: Extend CPU's cgroup controller |
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Hi Patrick,
On Monday 08 Jul 2019 at 09:43:53 (+0100), Patrick Bellasi wrote: > +static inline int uclamp_scale_from_percent(char *buf, u64 *value) > +{ > + *value = SCHED_CAPACITY_SCALE; > + > + buf = strim(buf); > + if (strncmp("max", buf, 4)) { > + s64 percent; > + int ret; > + > + ret = cgroup_parse_float(buf, 2, &percent); > + if (ret) > + return ret; > + > + percent <<= SCHED_CAPACITY_SHIFT; > + *value = DIV_ROUND_CLOSEST_ULL(percent, 10000); > + } > + > + return 0; > +} > + > +static inline u64 uclamp_percent_from_scale(u64 value) > +{ > + return DIV_ROUND_CLOSEST_ULL(value * 10000, SCHED_CAPACITY_SCALE); > +}
FWIW, I tried the patches and realized these conversions result in a 'funny' behaviour from a user's perspective. Things like this happen:
$ echo 20 > cpu.uclamp.min $ cat cpu.uclamp.min 20.2 $ echo 20.2 > cpu.uclamp.min $ cat cpu.uclamp.min 20.21
Having looked at the code, I get why this is happening, but I'm not sure if a random user will. It's not an issue per se, but it's just a bit weird.
I guess one way to fix this would be to revert back to having a 1024-scale for the cgroup interface too ... Though I understand Tejun wanted % for consistency with other things.
So, I'm not sure if this is still up for discussion, but in any case I wanted to say I support your original idea of using a 1024-scale for the cgroups interface, since that would solve the 'issue' above and keeps things consistent with the per-task API too.
Thanks, Quentin
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