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Date: Thu, 18 Apr 2024 10:50:47 +0800
From: Xuewen Yan <xuewen.yan94@...il.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Xuewen Yan <xuewen.yan@...soc.com>, mingo@...hat.com, juri.lelli@...hat.com,
vincent.guittot@...aro.org, dietmar.eggemann@....com, rostedt@...dmis.org,
bsegall@...gle.com, mgorman@...e.de, bristot@...hat.com, vschneid@...hat.com,
wuyun.abel@...edance.com, ke.wang@...soc.com, linux-kernel@...r.kernel.org,
Chen Yu <yu.c.chen@...el.com>
Subject: Re: [PATCH] sched/eevdf: Prevent vlag from exceeding the limit value
Hi Peter,
Sorry for the late reply.
On Mon, Apr 8, 2024 at 8:06 PM Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Tue, Jan 30, 2024 at 04:06:43PM +0800, Xuewen Yan wrote:
> > There are some scenarios here that will cause vlag to
> > exceed eevdf's limit.
> >
> > 1. In set_next_entity, it will stash a copy of deadline
> > at the point of pick in vlag, and if the task fork child,
> > the child's vlag would inherit parent's vlag, as a result,
> > the child's vlag is equal to the deadline. And then,
> > when place_entity, because the se's vlag is wrong, it would
> > cause vruntime and deadline update error.
>
> But __sched_fork() clears it? Or am I missing something subtle?
Yes, you are right, I missed the __sched_fork().
>
> > 2. When reweight_entity, the vlag would be recalculated,
> > because the new weights are uncertain, and it may cause
> > the vlag to exceed eevdf's limit.
> >
> > In order to ensure that vlag does not exceed the limit,
> > separate the calculation of limit from the update_entity_lag
> > and create a new func limit_entity_lag. When the vlag is
> > updated, use this func to prevent vlag from exceeding the limit.
> >
> > And add check whether the se is forked in place_entity, and calc
> > the curr's vlag to update the se's vlag.
> >
> > Signed-off-by: Xuewen Yan <xuewen.yan@...soc.com>
> > ---
> > kernel/sched/fair.c | 28 +++++++++++++++++++++++++---
> > 1 file changed, 25 insertions(+), 3 deletions(-)
> >
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index 533547e3c90a..3fc99b4b8b41 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -696,15 +696,22 @@ u64 avg_vruntime(struct cfs_rq *cfs_rq)
> > *
> > * XXX could add max_slice to the augmented data to track this.
> > */
> > +static s64 limit_entity_lag(struct sched_entity *se, s64 lag)
> > +{
> > + s64 limit;
> > +
> > + limit = calc_delta_fair(max_t(u64, 2*se->slice, TICK_NSEC), se);
> > + return clamp(lag, -limit, limit);
> > +}
>
> I used to run with a trace_printk() in there to check how often this
> trips, can you readily trigger these sites, or do you have to work hard
> at it?
I can trigger this easily. And I add dump_stack, the case is much:
[ 11.372967] Call trace:
[ 11.372971] dump_backtrace+0xec/0x138
[ 11.372990] show_stack+0x18/0x24
[ 11.372995] dump_stack_lvl+0x60/0x84
[ 11.373002] dump_stack+0x18/0x24
[ 11.373007] place_entity+0x210/0x25c
[ 11.373015] enqueue_task_fair+0x1e0/0x658
[ 11.373021] enqueue_task+0x94/0x188
[ 11.373028] ttwu_do_activate+0xb4/0x27c
[ 11.373034] try_to_wake_up+0x2fc/0x800
[ 11.373040] wake_up_q+0x70/0xd8
[ 11.373046] futex_wake+0x1e4/0x32c
[ 11.373052] do_futex+0x144/0x27c
[ 11.373056] __arm64_sys_futex_time32+0xa8/0x1b8
[ 11.373061] invoke_syscall+0x58/0x114
[ 11.373068] el0_svc_common+0xac/0xe0
[ 11.373074] do_el0_svc_compat+0x1c/0x28
[ 11.373079] el0_svc_compat+0x38/0x6c
[ 11.373085] el0t_32_sync_handler+0x60/0x8c
[ 11.373091] el0t_32_sync+0x1ac/0x1b0
[ 11.373097] the lag=4562177811 vruntime=18058609737 limit=3071999998
[ 38.778444] Call trace:
[ 38.778447] dump_backtrace+0xec/0x138
[ 38.778465] show_stack+0x18/0x24
[ 38.778470] dump_stack_lvl+0x60/0x84
[ 38.778479] dump_stack+0x18/0x24
[ 38.778484] place_entity+0x210/0x25c
[ 38.778492] enqueue_task_fair+0x1e0/0x658
[ 38.778498] enqueue_task+0x94/0x188
[ 38.778505] ttwu_do_activate+0xb4/0x27c
[ 38.778512] try_to_wake_up+0x2fc/0x800
[ 38.778518] wake_up_process+0x18/0x28
[ 38.778523] hrtimer_wakeup+0x20/0x94
[ 38.778530] __hrtimer_run_queues+0x19c/0x39c
[ 38.778536] hrtimer_interrupt+0xdc/0x39c
[ 38.778541] arch_timer_handler_phys+0x50/0x64
[ 38.778549] handle_percpu_devid_irq+0xb4/0x258
[ 38.778556] generic_handle_domain_irq+0x44/0x60
[ 38.778563] gic_handle_irq+0x4c/0x114
[ 38.778568] call_on_irq_stack+0x3c/0x74
[ 38.778573] do_interrupt_handler+0x4c/0x84
[ 38.778580] el0_interrupt+0x54/0xe4
[ 38.778586] __el0_irq_handler_common+0x18/0x28
[ 38.778591] el0t_64_irq_handler+0x10/0x1c
[ 38.778596] el0t_64_irq+0x1a8/0x1ac
[ 38.778602] the lag=-993821948 vruntime=162909998203 limit=877714284
[ 41.205507] Call trace:
[ 41.205508] dump_backtrace+0xec/0x138
[ 41.205516] show_stack+0x18/0x24
[ 41.205518] dump_stack_lvl+0x60/0x84
[ 41.205523] dump_stack+0x18/0x24
[ 41.205526] place_entity+0x210/0x25c
[ 41.205530] enqueue_task_fair+0x1e0/0x658
[ 41.205533] enqueue_task+0x94/0x188
[ 41.205537] ttwu_do_activate+0xb4/0x27c
[ 41.205540] try_to_wake_up+0x2fc/0x800
[ 41.205543] default_wake_function+0x20/0x38
[ 41.205547] autoremove_wake_function+0x18/0x7c
[ 41.205551] receiver_wake_function+0x28/0x38
[ 41.205555] __wake_up_common+0xe8/0x188
[ 41.205558] __wake_up_sync_key+0x88/0x144
[ 41.205561] sock_def_readable+0xb4/0x1ac
[ 41.205565] unix_dgram_sendmsg+0x5b4/0x764
[ 41.205569] sock_write_iter+0xe0/0x160
[ 41.205571] do_iter_write+0x210/0x338
[ 41.205575] do_writev+0xd8/0x198
[ 41.205577] __arm64_sys_writev+0x20/0x30
[ 41.205581] invoke_syscall+0x58/0x114
[ 41.205584] el0_svc_common+0x80/0xe0
[ 41.205588] do_el0_svc+0x1c/0x28
[ 41.205591] el0_svc+0x3c/0x70
[ 41.205594] el0t_64_sync_handler+0x68/0xbc
[ 41.205597] el0t_64_sync+0x1a8/0x1ac
[ 41.205599] the lag=-7374172458 vruntime=209576555829 limit=3071999998
[ 41.416780] Call trace:
[ 41.416781] dump_backtrace+0xec/0x138
[ 41.416788] show_stack+0x18/0x24
[ 41.416791] dump_stack_lvl+0x60/0x84
[ 41.416797] dump_stack+0x18/0x24
[ 41.416799] place_entity+0x210/0x25c
[ 41.416804] enqueue_task_fair+0x1e0/0x658
[ 41.416807] enqueue_task+0x94/0x188
[ 41.416811] ttwu_do_activate+0xb4/0x27c
[ 41.416814] try_to_wake_up+0x2fc/0x800
[ 41.416818] default_wake_function+0x20/0x38
[ 41.416821] autoremove_wake_function+0x18/0x7c
[ 41.416825] __wake_up_common+0xe8/0x188
[ 41.416828] __wake_up_sync_key+0x88/0x144
[ 41.416831] __wake_up_sync+0x14/0x24
[ 41.416834] binder_transaction+0x1794/0x1e98
[ 41.416838] binder_ioctl_write_read+0x590/0x3950
[ 41.416841] binder_ioctl+0x1ec/0xa40
[ 41.416844] __arm64_sys_ioctl+0xa8/0xe4
[ 41.416849] invoke_syscall+0x58/0x114
[ 41.416853] el0_svc_common+0x80/0xe0
[ 41.416857] do_el0_svc+0x1c/0x28
[ 41.416860] el0_svc+0x3c/0x70
[ 41.416868] the lag=3625583753 vruntime=254849351272 limit=3071999998
[ 41.416863] el0t_64_sync_handler+0x68/0xbc
[ 41.416866] el0t_64_sync+0x1a8/0x1ac
Thanks!
BR
---
xuewen
>
>
> > static void update_entity_lag(struct cfs_rq *cfs_rq, struct sched_entity *se)
> > {
> > - s64 lag, limit;
> > + s64 lag;
> >
> > SCHED_WARN_ON(!se->on_rq);
> > lag = avg_vruntime(cfs_rq) - se->vruntime;
> >
> > - limit = calc_delta_fair(max_t(u64, 2*se->slice, TICK_NSEC), se);
> > - se->vlag = clamp(lag, -limit, limit);
> > + se->vlag = limit_entity_lag(se, lag);
> > }
> >
> > /*
> > @@ -3757,6 +3764,7 @@ static void reweight_eevdf(struct cfs_rq *cfs_rq, struct sched_entity *se,
> > if (avruntime != se->vruntime) {
> > vlag = (s64)(avruntime - se->vruntime);
> > vlag = div_s64(vlag * old_weight, weight);
> > + vlag = limit_entity_lag(se, vlag);
> > se->vruntime = avruntime - vlag;
> > }
> >
> > @@ -3804,6 +3812,9 @@ static void reweight_entity(struct cfs_rq *cfs_rq, struct sched_entity *se,
> >
> > update_load_set(&se->load, weight);
> >
> > + if (!se->on_rq)
> > + se-vlag = limit_entity_lag(se, se->vlag);
> > +
> > #ifdef CONFIG_SMP
> > do {
> > u32 divider = get_pelt_divider(&se->avg);
>
> > @@ -5237,6 +5258,7 @@ place_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
> > if (WARN_ON_ONCE(!load))
> > load = 1;
> > lag = div_s64(lag, load);
> > + lag = limit_entity_lag(se, lag);
> > }
> >
> > se->vruntime = vruntime - lag;
> > --
> > 2.25.1
> >
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