Re: [PATCH] sched/uclamp: Fix uclamp_tg_restrict()
From: Xuewen Yan
Date: Tue Jun 15 2021 - 23:07:20 EST
Hi Qais
Sorry for the late reply.
I tested the patch on the "UNISOC T610" platform, and it looks fine.
According to the two cases:
case1:
without patch:
set task's clamp_min=614(60%), clamp_max=819(80%), the result as:
[ 215.780435]c6 uclamp_test :
pid=138,req_min=614,req_max=819,eff_min=614,eff_max=819
after set tg's cpu.uclamp.max = 50%，the result:
[ 420.580443]c6 uclamp_test :
pid=138,req_min=614,req_max=819,eff_min=614,eff_max=512
with patch:
set task's clamp_min=614(60%), clamp_max=819(80%), the result as:
[ 333.533878]c7 uclamp_test :
pid=138,req_min=614,req_max=819,eff_min=614,eff_max=819
after set tg's cpu.uclamp.max = 50%，the result:
[ 430.813789]c6 uclamp_test :
pid=138,req_min=614,req_max=819,eff_min=512,eff_max=512
case2:
without patch:
set task's clamp_min=614(60%), clamp_max=819(80%), the result as:
[ 169.700544]c0 uclamp_test :
pid=137,req_min=0,req_max=209,eff_min=0,eff_max=209
after set tg's cpu.uclamp.min = 30%, tg's cpu.uclamp.max = 50%，the result:
[ 246.500634]c7 uclamp_test :
pid=137,req_min=0,req_max=209,eff_min=307,eff_max=209
with patch:
set task's clamp_min=0(0%), clamp_max=209(20%), the result as:
[ 169.700544]c0 uclamp_test :
pid=137,req_min=0,req_max=209,eff_min=0,eff_max=209
after set tg's cpu.uclamp.min = 30%, tg's cpu.uclamp.max = 50%，the result:
[ 179.933868]c6 uclamp_test :
pid=137,req_min=0,req_max=209,eff_min=307,eff_max=307
---
Cheers
xuewen
On Fri, Jun 11, 2021 at 8:23 PM Qais Yousef <qais.yousef@xxxxxxx> wrote:
>
> Now cpu.uclamp.min acts as a protection, we need to make sure that the
> uclamp request of the task is within the allowed range of the cgroup,
> that is it is clamp()'ed correctly by tg->uclamp[UCLAMP_MIN] and
> tg->uclamp[UCLAMP_MAX].
>
> As reported by Xuewen [1] we can have some corner cases where there's
> inverstion between uclamp requested by task (p) and the uclamp values of
> the taskgroup it's attached to (tg). Following table demonstrates
> 2 corner cases:
>
> | p | tg | effective
> -----------+-----+------+-----------
> CASE 1
> -----------+-----+------+-----------
> uclamp_min | 60% | 0% | 60%
> -----------+-----+------+-----------
> uclamp_max | 80% | 50% | 50%
> -----------+-----+------+-----------
> CASE 2
> -----------+-----+------+-----------
> uclamp_min | 0% | 30% | 30%
> -----------+-----+------+-----------
> uclamp_max | 20% | 50% | 20%
> -----------+-----+------+-----------
>
> With this fix we get:
>
> | p | tg | effective
> -----------+-----+------+-----------
> CASE 1
> -----------+-----+------+-----------
> uclamp_min | 60% | 0% | 50%
> -----------+-----+------+-----------
> uclamp_max | 80% | 50% | 50%
> -----------+-----+------+-----------
> CASE 2
> -----------+-----+------+-----------
> uclamp_min | 0% | 30% | 30%
> -----------+-----+------+-----------
> uclamp_max | 20% | 50% | 30%
> -----------+-----+------+-----------
>
> Additionally uclamp_update_active_tasks() must now unconditionally
> update both UCLAMP_MIN/MAX because changing the tg's UCLAMP_MAX for
> instance could have an impact on the effective UCLAMP_MIN of the tasks.
>
> | p | tg | effective
> -----------+-----+------+-----------
> old
> -----------+-----+------+-----------
> uclamp_min | 60% | 0% | 50%
> -----------+-----+------+-----------
> uclamp_max | 80% | 50% | 50%
> -----------+-----+------+-----------
> *new*
> -----------+-----+------+-----------
> uclamp_min | 60% | 0% | *60%*
> -----------+-----+------+-----------
> uclamp_max | 80% |*70%* | *70%*
> -----------+-----+------+-----------
>
> [1] https://lore.kernel.org/lkml/CAB8ipk_a6VFNjiEnHRHkUMBKbA+qzPQvhtNjJ_YNzQhqV_o8Zw@xxxxxxxxxxxxxx/
>
> Reported-by: Xuewen Yan <xuewen.yan94@xxxxxxxxx>
> Fixes: 0c18f2ecfcc2 ("sched/uclamp: Fix wrong implementation of cpu.uclamp.min")
> Signed-off-by: Qais Yousef <qais.yousef@xxxxxxx>
> ---
>
> Xuewen, Yun, Wei
>
> If you can give this a spin and provide Tested-by that would be much
> appreciated.
>
> Thanks!
>
>
> kernel/sched/core.c | 43 +++++++++++++++----------------------------
> 1 file changed, 15 insertions(+), 28 deletions(-)
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 9e9a5be35cde..0318b00baa97 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -1403,38 +1403,28 @@ static void uclamp_sync_util_min_rt_default(void)
> static inline struct uclamp_se
> uclamp_tg_restrict(struct task_struct *p, enum uclamp_id clamp_id)
> {
> - struct uclamp_se uc_req = p->uclamp_req[clamp_id];
> + /* Copy by value as we could modify it */
> + struct uclamp_se uc_eff = p->uclamp_req[clamp_id];
> #ifdef CONFIG_UCLAMP_TASK_GROUP
> + unsigned int tg_min, tg_max, value;
>
> /*
> * Tasks in autogroups or root task group will be
> * restricted by system defaults.
> */
> if (task_group_is_autogroup(task_group(p)))
> - return uc_req;
> + return uc_eff;
> if (task_group(p) == &root_task_group)
> - return uc_req;
> + return uc_eff;
>
> - 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;
> - }
> - case UCLAMP_MAX: {
> - struct uclamp_se uc_max = task_group(p)->uclamp[clamp_id];
> - if (uc_req.value > uc_max.value)
> - return uc_max;
> - break;
> - }
> - default:
> - WARN_ON_ONCE(1);
> - break;
> - }
> + tg_min = task_group(p)->uclamp[UCLAMP_MIN].value;
> + tg_max = task_group(p)->uclamp[UCLAMP_MAX].value;
> + value = uc_eff.value;
> + value = clamp(value, tg_min, tg_max);
> + uclamp_se_set(&uc_eff, value, false);
> #endif
>
> - return uc_req;
> + return uc_eff;
> }
>
> /*
> @@ -1661,8 +1651,7 @@ uclamp_update_active(struct task_struct *p, enum uclamp_id clamp_id)
>
> #ifdef CONFIG_UCLAMP_TASK_GROUP
> static inline void
> -uclamp_update_active_tasks(struct cgroup_subsys_state *css,
> - unsigned int clamps)
> +uclamp_update_active_tasks(struct cgroup_subsys_state *css)
> {
> enum uclamp_id clamp_id;
> struct css_task_iter it;
> @@ -1670,10 +1659,8 @@ uclamp_update_active_tasks(struct cgroup_subsys_state *css,
>
> css_task_iter_start(css, 0, &it);
> while ((p = css_task_iter_next(&it))) {
> - for_each_clamp_id(clamp_id) {
> - if ((0x1 << clamp_id) & clamps)
> - uclamp_update_active(p, clamp_id);
> - }
> + for_each_clamp_id(clamp_id)
> + uclamp_update_active(p, clamp_id);
> }
> css_task_iter_end(&it);
> }
> @@ -9626,7 +9613,7 @@ static void cpu_util_update_eff(struct cgroup_subsys_state *css)
> }
>
> /* Immediately update descendants RUNNABLE tasks */
> - uclamp_update_active_tasks(css, clamps);
> + uclamp_update_active_tasks(css);
> }
> }
>
> --
> 2.25.1
>