Messages in this thread | | | From | Xuewen Yan <> | Date | Sat, 5 Jun 2021 10:12:29 +0800 | Subject | Re: [PATCH] sched/uclamp: Avoid setting cpu.uclamp.min bigger than cpu.uclamp.max |
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Hi Qais,
On Sat, Jun 5, 2021 at 12:08 AM Qais Yousef <qais.yousef@arm.com> wrote: > > On 06/03/21 10:24, Xuewen Yan wrote: > > +CC Qais > > Thanks for the CC :) > > > > > > > Hi Quentin > > > > On Wed, Jun 2, 2021 at 9:22 PM Quentin Perret <qperret@google.com> wrote: > > > > > > +CC Patrick and Tejun > > > > > > On Wednesday 02 Jun 2021 at 20:38:03 (+0800), Xuewen Yan wrote: > > > > From: Xuewen Yan <xuewen.yan@unisoc.com> > > > > > > > > When setting cpu.uclamp.min/max in cgroup, there is no validating > > > > like uclamp_validate() in __sched_setscheduler(). It may cause the > > > > cpu.uclamp.min is bigger than cpu.uclamp.max. > > > > > > ISTR this was intentional. We also allow child groups to ask for > > > whatever clamps they want, but that is always limited by the parent, and > > > reflected in the 'effective' values, as per the cgroup delegation model. > > As Quentin said. This intentional to comply with cgroup model. > > See Limits and Protections sections in Documentation/admin-guide/cgroup-v2.rst > > Specifically > > "all configuration combinations are valid" > > So user can set cpu.uclamp.min higher than cpu.uclamp.max. But when we apply > the setting, cpu.uclamp.min will be capped by cpu.uclamp.max. I can see you > found the cpu_util_update_eff() logic. >
Thanks a lot for your patience to explain, sorry for my ignorance of Documentation/admin-guide/cgroup-v2.rst.
> > > > It does not affect the 'effective' value. That because there is > > protection in cpu_util_update_eff(): > > /* Ensure protection is always capped by limit */ > > eff[UCLAMP_MIN] = min(eff[UCLAMP_MIN], eff[UCLAMP_MAX]); > > > > When users set the cpu.uclamp.min > cpu.uclamp.max: > > cpu.uclamp.max = 50; > > to set : cpu.uclamp.min = 60; > > That would make the uclamp_req[UCLAMP_MIN].value = 1024* 60% = 614, > > uclamp_req[UCLAMP_MAX].value = 1024* 50% = 512; > > But finally, the uclamp[UCLAMP_MIN].value = uclamp[UCLAMP_MAX].value > > = 1024* 50% = 512; > > > > Is it deliberately set not to validate because of the above? > > Sorry I'm not following you here. What code paths were you trying to explain > here? > > Did you actually hit any problem here?
I just gave an example of the difference of uclamp_req and uclamp without my patch, and can ignore it.
> In addition,In your patch: 6938840392c89 ("sched/uclamp: Fix wrong implementation of cpu.uclamp.min") https://lkml.kernel.org/r/20210510145032.1934078-2-qais.yousef@arm.com
+ switch (clamp_id) { + case UCLAMP_MIN: { + struct uclamp_se uc_min = task_group(p)->uclamp[clamp_id]; + if (uc_req.value < uc_min.value) + return uc_min; + break;
When the clamp_id = UCLAMP_MIN, why not judge the uc_req.value is bigger than task_group(p)->uclamp[UCLAMP_MAX] ? Because when the p->uclamp_req[UCLAMP_MIN] > task_group(p)->uclamp[UCLAMP_MAX], the patch can not clamp the p->uclamp_req[UCLAMP_MIN/MAX] into [ task_group(p)->uclamp[UCLAMP_MAX], task_group(p)->uclamp[UCLAMP_MAX] ].
Is it necessary to fix it here?
Thanks xuewen
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