Hi Patrick, On Wed, Oct 28, 2020 at 11:11:07AM +0100, Patrick Bellasi wrote: > > Hi Dietmar, Yun, > I hope I'm not too late before v4 posting ;) > > I think the overall approach is sound, I just added in a couple of > cleanups and a possible fix (user_defined reset). > > Best, > Patrick > > > On Tue, Oct 27, 2020 at 16:58:13 +0100, Yun Hsiang <hsiang023...@gmail.com> > wrote... > > > Hi Diet mar, > > On Mon, Oct 26, 2020 at 08:00:48PM +0100, Dietmar Eggemann wrote: > >> On 26/10/2020 16:45, Yun Hsiang wrote: > > [...] > > >> I thought about something like this. Only lightly tested. > >> > >> ---8<--- > >> > >> From: Dietmar Eggemann <dietmar.eggem...@arm.com> > >> Date: Mon, 26 Oct 2020 13:52:23 +0100 > >> Subject: [PATCH] SCHED_FLAG_UTIL_CLAMP_RESET > >> > >> Signed-off-by: Dietmar Eggemann <dietmar.eggem...@arm.com> > >> --- > >> include/uapi/linux/sched.h | 4 +++- > >> kernel/sched/core.c | 31 +++++++++++++++++++++++++++---- > >> 2 files changed, 30 insertions(+), 5 deletions(-) > >> > >> diff --git a/include/uapi/linux/sched.h b/include/uapi/linux/sched.h > >> index 3bac0a8ceab2..0dd890822751 100644 > >> --- a/include/uapi/linux/sched.h > >> +++ b/include/uapi/linux/sched.h > >> @@ -132,12 +132,14 @@ struct clone_args { > >> #define SCHED_FLAG_KEEP_PARAMS 0x10 > >> #define SCHED_FLAG_UTIL_CLAMP_MIN 0x20 > >> #define SCHED_FLAG_UTIL_CLAMP_MAX 0x40 > >> +#define SCHED_FLAG_UTIL_CLAMP_RESET 0x80 > >> > >> #define SCHED_FLAG_KEEP_ALL (SCHED_FLAG_KEEP_POLICY | \ > >> SCHED_FLAG_KEEP_PARAMS) > >> > >> #define SCHED_FLAG_UTIL_CLAMP (SCHED_FLAG_UTIL_CLAMP_MIN | \ > >> - SCHED_FLAG_UTIL_CLAMP_MAX) > >> + SCHED_FLAG_UTIL_CLAMP_MAX | \ > >> + SCHED_FLAG_UTIL_CLAMP_RESET) > >> > >> #define SCHED_FLAG_ALL (SCHED_FLAG_RESET_ON_FORK | \ > >> SCHED_FLAG_RECLAIM | \ > >> diff --git a/kernel/sched/core.c b/kernel/sched/core.c > >> index 3dc415f58bd7..717b1cf5cf1f 100644 > >> --- a/kernel/sched/core.c > >> +++ b/kernel/sched/core.c > >> @@ -1438,6 +1438,23 @@ static int uclamp_validate(struct task_struct *p, > >> return 0; > >> } > >> > >> +static bool uclamp_reset(enum uclamp_id clamp_id, unsigned long flags) > >> +{ > > Maybe we can add in some comments? > I'll add these comment. > > /* No _UCLAMP_RESET flag set: do not reset */ > >> + if (!(flags & SCHED_FLAG_UTIL_CLAMP_RESET)) > >> + return false; > >> + > > /* Only _UCLAMP_RESET flag set: reset both clamps */ > >> + if (!(flags & (SCHED_FLAG_UTIL_CLAMP_MIN | SCHED_FLAG_UTIL_CLAMP_MAX))) > >> + return true; > >> + > /* Both _UCLAMP_RESET and _UCLAMP_MIN flags are set: reset only min */ > >> + if ((flags & SCHED_FLAG_UTIL_CLAMP_MIN) && clamp_id == UCLAMP_MIN) > >> + return true; > >> + > > /* Both _UCLAMP_RESET and _UCLAMP_MAX flags are set: reset only max */ > >> + if ((flags & SCHED_FLAG_UTIL_CLAMP_MAX) && clamp_id == UCLAMP_MAX) > >> + return true; > > Since the evaluation ordering is important, do we have to better > _always_ use a READ_ONCE() for all flags accesses above, to ensure it is > preserved? >
Is this mean that we want to use READ_ONCE to avoid compiler reordering these conditions? > >> + > >> + return false; > >> +} > >> + > >> static void __setscheduler_uclamp(struct task_struct *p, > >> const struct sched_attr *attr) > >> { > >> @@ -1449,24 +1466,30 @@ static void __setscheduler_uclamp(struct > >> task_struct *p, > >> */ > > Perhaps we should update the comment above this loop with something > like: > > /* > * Reset to default clamps on forced _UCLAMP_RESET (always) and > * for tasks without a task-specific value (on scheduling class > change). > */ > >> for_each_clamp_id(clamp_id) { > >> struct uclamp_se *uc_se = &p->uclamp_req[clamp_id]; > >> + unsigned int value; > >> > >> /* Keep using defined clamps across class changes */ > >> - if (uc_se->user_defined) > >> + if (!uclamp_reset(clamp_id, attr->sched_flags) && > >> + uc_se->user_defined) { > >> continue; > >> + } > > I think we miss to reset the user_defined flag here. > > What about replacing the above chunk with: > > if (uclamp_reset(clamp_id, attr->sched_flags)) > uc_se->user_defined = false; > if (uc-se->user_defined) > continue; > > ? user_defined flag will be reset later by uclamp_se_set(uc_se, value, false). But I agree to split it to two condition because it seems clearer. > > > >> > >> /* > >> * RT by default have a 100% boost value that could be modified > >> * at runtime. > >> */ > >> if (unlikely(rt_task(p) && clamp_id == UCLAMP_MIN)) > >> - __uclamp_update_util_min_rt_default(p); > >> + value = sysctl_sched_uclamp_util_min_rt_default; > > By removing this usage of __uclamp_updadate_util_min_rt_default(p), > the only other usage remaining is the call from: > uclamp_udpate_util_min_rt_default(). > > What about an additional cleanup by in-lining the only surviving usage? > > > >> else > >> - uclamp_se_set(uc_se, uclamp_none(clamp_id), false); > >> + value = uclamp_none(clamp_id); > >> > >> + uclamp_se_set(uc_se, value, false); > >> } > >> > >> - if (likely(!(attr->sched_flags & SCHED_FLAG_UTIL_CLAMP))) > >> + if (likely(!(attr->sched_flags & SCHED_FLAG_UTIL_CLAMP)) || > >> + attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_RESET) { > > The likely() above should not wrap both conditions to be effective? Got it. > > >> return; > >> + } > >> > >> if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MIN) { > >> uclamp_se_set(&p->uclamp_req[UCLAMP_MIN],