Hello Johannes, 在 2021/2/9 下午11:48, Johannes Weiner 写道: > Hello Chengming, > > On Tue, Feb 09, 2021 at 03:10:33PM +0800, Chengming Zhou wrote: >> When the current task in a cgroup is in_memstall, the corresponding groupc >> on that cpu is in PSI_MEM_FULL state, so we can exploit that to remove the >> redundant psi_task_tick from scheduler_tick to save this periodic cost. > Can you please update the patch name and the changelog to the new > version of the patch? It's not removing the redundant tick, it's > moving the reclaim detection from the timer tick to the task state > tracking machinery using the recently added ONCPU state.
Yes, I will change the name and changelog, it will be clearer for this patch : ) >> Signed-off-by: Muchun Song <[email protected]> >> Signed-off-by: Chengming Zhou <[email protected]> >> --- >> include/linux/psi.h | 1 - >> kernel/sched/core.c | 1 - >> kernel/sched/psi.c | 49 ++++++++++++++----------------------------------- >> kernel/sched/stats.h | 9 --------- >> 4 files changed, 14 insertions(+), 46 deletions(-) >> >> diff --git a/include/linux/psi.h b/include/linux/psi.h >> index 7361023f3fdd..65eb1476ac70 100644 >> --- a/include/linux/psi.h >> +++ b/include/linux/psi.h >> @@ -20,7 +20,6 @@ void psi_task_change(struct task_struct *task, int clear, >> int set); >> void psi_task_switch(struct task_struct *prev, struct task_struct *next, >> bool sleep); >> >> -void psi_memstall_tick(struct task_struct *task, int cpu); >> void psi_memstall_enter(unsigned long *flags); >> void psi_memstall_leave(unsigned long *flags); >> >> diff --git a/kernel/sched/core.c b/kernel/sched/core.c >> index 15d2562118d1..31788a9b335b 100644 >> --- a/kernel/sched/core.c >> +++ b/kernel/sched/core.c >> @@ -4533,7 +4533,6 @@ void scheduler_tick(void) >> update_thermal_load_avg(rq_clock_thermal(rq), rq, thermal_pressure); >> curr->sched_class->task_tick(rq, curr, 0); >> calc_global_load_tick(rq); >> - psi_task_tick(rq); >> >> rq_unlock(rq, &rf); >> >> diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c >> index 2293c45d289d..6e46d9eb279b 100644 >> --- a/kernel/sched/psi.c >> +++ b/kernel/sched/psi.c >> @@ -644,8 +644,7 @@ static void poll_timer_fn(struct timer_list *t) >> wake_up_interruptible(&group->poll_wait); >> } >> >> -static void record_times(struct psi_group_cpu *groupc, int cpu, >> - bool memstall_tick) >> +static void record_times(struct psi_group_cpu *groupc, int cpu) >> { >> u32 delta; >> u64 now; >> @@ -664,23 +663,6 @@ static void record_times(struct psi_group_cpu *groupc, >> int cpu, >> groupc->times[PSI_MEM_SOME] += delta; >> if (groupc->state_mask & (1 << PSI_MEM_FULL)) >> groupc->times[PSI_MEM_FULL] += delta; >> - else if (memstall_tick) { >> - u32 sample; >> - /* >> - * Since we care about lost potential, a >> - * memstall is FULL when there are no other >> - * working tasks, but also when the CPU is >> - * actively reclaiming and nothing productive >> - * could run even if it were runnable. >> - * >> - * When the timer tick sees a reclaiming CPU, >> - * regardless of runnable tasks, sample a FULL >> - * tick (or less if it hasn't been a full tick >> - * since the last state change). >> - */ >> - sample = min(delta, (u32)jiffies_to_nsecs(1)); >> - groupc->times[PSI_MEM_FULL] += sample; >> - } >> } >> >> if (groupc->state_mask & (1 << PSI_CPU_SOME)) { >> @@ -714,7 +696,7 @@ static void psi_group_change(struct psi_group *group, >> int cpu, >> */ >> write_seqcount_begin(&groupc->seq); >> >> - record_times(groupc, cpu, false); >> + record_times(groupc, cpu); >> >> for (t = 0, m = clear; m; m &= ~(1 << t), t++) { >> if (!(m & (1 << t))) >> @@ -738,6 +720,18 @@ static void psi_group_change(struct psi_group *group, >> int cpu, >> if (test_state(groupc->tasks, s)) >> state_mask |= (1 << s); >> } >> + >> + /* >> + * Since we care about lost potential, a memstall is FULL >> + * when there are no other working tasks, but also when >> + * the CPU is actively reclaiming and nothing productive >> + * could run even if it were runnable. So when the current >> + * task in a cgroup is in_memstall, the corresponding groupc >> + * on that cpu is in PSI_MEM_FULL state. >> + */ >> + if (groupc->tasks[NR_ONCPU] && cpu_curr(cpu)->in_memstall) >> + state_mask |= (1 << PSI_MEM_FULL); > This doesn't really work with the psi_task_switch() optimization. If > we switch between two tasks inside a leaf group, where one is memstall > and the other is not, we don't update the parents properly. So you > need another branch in there as well for checking memstall. At which > point the timer tick implementation is likely cheaper and simpler... Thank you for pointing out this. I will add another branch there to check memstall to update the parents properly and send a patch-v2. Thanks. >> @@ -144,14 +144,6 @@ static inline void psi_sched_switch(struct task_struct >> *prev, >> psi_task_switch(prev, next, sleep); >> } >> >> -static inline void psi_task_tick(struct rq *rq) >> -{ >> - if (static_branch_likely(&psi_disabled)) >> - return; >> - >> - if (unlikely(rq->curr->in_memstall)) >> - psi_memstall_tick(rq->curr, cpu_of(rq)); >> -} >> #else /* CONFIG_PSI */ >> static inline void psi_enqueue(struct task_struct *p, bool wakeup) {} >> static inline void psi_dequeue(struct task_struct *p, bool sleep) {}
