Re: [PATCH v2 net 3/7] net/sched: taprio: update impacted fields during cycle time adjustment

Abdul Rahim, Faizal
2023-11-15T11:55:55Z

On 9/11/2023 7:41 am, Vladimir Oltean wrote:
> On Tue, Nov 07, 2023 at 06:20:19AM -0500, Faizal Rahim wrote:
>> Update impacted fields in advance_sched() if cycle_corr_active()
>> is true, which indicates that the next entry is the last entry
>> from oper that it will run.
>>
>> Update impacted fields:
>>
>> 1. gate_duration[tc], max_open_gate_duration[tc]
>> Created a new API update_open_gate_duration().The API sets the
>> duration based on the last remaining entry, the original value
>> was based on consideration of multiple entries.
>>
>> 2. gate_close_time[tc]
>> Update next entry gate close time according to the new admin
>> base time
>>
>> 3. max_sdu[tc], budget[tc]
>> Restrict from setting to max value because there's only a single
>> entry left to run from oper before changing to the new admin
>> schedule, so we shouldn't set to max.
>>
>> Signed-off-by: Faizal Rahim <faizal.abdul.rahim@linux.intel.com>
>
> The commit message shouldn't be a text-to-speech output of the commit body.
> Say very shortly how the system should behave, what's wrong such that it
> doesn't behave as expected, what's the user-visible impact of the bug,
> and try to identify why the bug happened.
>
> In this case, what happened is that commit a306a90c8ffe ("net/sched:
> taprio: calculate tc gate durations"), which introduced the impacted
> fields you are changing, never took dynamic schedule changes into
> consideration. So this commit should also appear in the Fixes: tag.

Got it.

>> ---
>> net/sched/sch_taprio.c | 49 +++++++++++++++++++++++++++++++++++++++---
>> 1 file changed, 46 insertions(+), 3 deletions(-)
>>
>> diff --git a/net/sched/sch_taprio.c b/net/sched/sch_taprio.c
>> index ed32654b46f5..119dec3bbe88 100644
>> --- a/net/sched/sch_taprio.c
>> +++ b/net/sched/sch_taprio.c
>> @@ -288,7 +288,8 @@ static void taprio_update_queue_max_sdu(struct taprio_sched *q,
>> /* TC gate never closes => keep the queueMaxSDU
>> * selected by the user
>> */
>> - if (sched->max_open_gate_duration[tc] == sched->cycle_time) {
>> + if (sched->max_open_gate_duration[tc] == sched->cycle_time &&
>> + !cycle_corr_active(sched->cycle_time_correction)) {
>> max_sdu_dynamic = U32_MAX;
>> } else {
>> u32 max_frm_len;
>> @@ -684,7 +685,8 @@ static void taprio_set_budgets(struct taprio_sched *q,
>>
>> for (tc = 0; tc < num_tc; tc++) {
>> /* Traffic classes which never close have infinite budget */
>> - if (entry->gate_duration[tc] == sched->cycle_time)
>> + if (entry->gate_duration[tc] == sched->cycle_time &&
>> + !cycle_corr_active(sched->cycle_time_correction))
>> budget = INT_MAX;
>> else
>> budget = div64_u64((u64)entry->gate_duration[tc] * PSEC_PER_NSEC,
>> @@ -896,6 +898,32 @@ static bool should_restart_cycle(const struct sched_gate_list *oper,
>> return false;
>> }
>>
>> +/* Open gate duration were calculated at the beginning with consideration of
>> + * multiple entries. If cycle time correction is active, there's only a single
>> + * remaining entry left from oper to run.
>> + * Update open gate duration based on this last entry.
>> + */
>> +static void update_open_gate_duration(struct sched_entry *entry,
>> + struct sched_gate_list *oper,
>> + int num_tc,
>> + u64 open_gate_duration)
>> +{
>> + int tc;
>> +
>> + if (!entry || !oper)
>> + return;
>> +
>> + for (tc = 0; tc < num_tc; tc++) {
>> + if (entry->gate_mask & BIT(tc)) {
>> + entry->gate_duration[tc] = open_gate_duration;
>> + oper->max_open_gate_duration[tc] = open_gate_duration;
>> + } else {
>> + entry->gate_duration[tc] = 0;
>> + oper->max_open_gate_duration[tc] = 0;
>> + }
>> + }
>> +}
>> +
>> static bool should_change_sched(struct sched_gate_list *oper)
>> {
>> bool change_to_admin_sched = false;
>> @@ -1010,13 +1038,28 @@ static enum hrtimer_restart advance_sched(struct hrtimer *timer)
>> /* The next entry is the last entry we will run from
>> * oper, subsequent ones will take from the new admin
>> */
>> + u64 new_gate_duration =
>> + next->interval + oper->cycle_time_correction;
>> + struct qdisc_size_table *stab =
>> + rtnl_dereference(q->root->stab);
>> +
>
> The lockdep annotation for this RCU accessor is bogus.
> rtnl_dereference() is the same as rcu_dereference_protected(..., lockdep_rtnl_is_held()),
> which cannot be true in a hrtimer callback, as the rtnetlink lock is a
> sleepable mutex and hrtimers run in atomic context.
>
> Running with lockdep enabled will tell you as much:
>
> $ ./test_taprio_cycle_extension.sh
> Testing config change with a delay of 5250000000 ns between schedules
> [ 100.734925]
> [ 100.736703] =============================
> [ 100.740780] WARNING: suspicious RCU usage
> [ 100.744857] 6.6.0-10114-gca572939947f #1495 Not tainted
> [ 100.750162] -----------------------------
> [ 100.754236] net/sched/sch_taprio.c:1064 suspicious rcu_dereference_protected() usage!
> [ 100.762155]
> [ 100.762155] other info that might help us debug this:
> [ 100.762155]
> [ 100.770242]
> [ 100.770242] rcu_scheduler_active = 2, debug_locks = 1
> [ 100.776851] 1 lock held by swapper/0/0:
> [ 100.780756] #0: ffff3d9784b83b00 (&q->current_entry_lock){-...}-{3:3}, at: advance_sched+0x44/0x59c
> [ 100.790099]
> [ 100.790099] stack backtrace:
> [ 100.794477] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 6.6.0-10114-gca572939947f #1495
> [ 100.802346] Hardware name: LS1028A RDB Board (DT)
> [ 100.807072] Call trace:
> [ 100.809531] dump_backtrace+0xf4/0x140
> [ 100.813305] show_stack+0x18/0x2c
> [ 100.816638] dump_stack_lvl+0x60/0x80
> [ 100.820321] dump_stack+0x18/0x24
> [ 100.823654] lockdep_rcu_suspicious+0x170/0x210
> [ 100.828210] advance_sched+0x384/0x59c
> [ 100.831978] __hrtimer_run_queues+0x200/0x430
> [ 100.836360] hrtimer_interrupt+0xdc/0x39c
> [ 100.840392] arch_timer_handler_phys+0x3c/0x4c
> [ 100.844862] handle_percpu_devid_irq+0xb8/0x28c
> [ 100.849417] generic_handle_domain_irq+0x2c/0x44
> [ 100.854060] gic_handle_irq+0x4c/0x110
> [ 100.857830] call_on_irq_stack+0x24/0x4c
> [ 100.861775] el1_interrupt+0x74/0xc0
> [ 100.865370] el1h_64_irq_handler+0x18/0x24
> [ 100.869489] el1h_64_irq+0x64/0x68
> [ 100.872909] arch_local_irq_enable+0x8/0xc
> [ 100.877032] cpuidle_enter+0x38/0x50
> [ 100.880629] do_idle+0x1ec/0x280
> [ 100.883877] cpu_startup_entry+0x34/0x38
> [ 100.887822] kernel_init+0x0/0x1a0
> [ 100.891245] start_kernel+0x0/0x3b0
> [ 100.894756] start_kernel+0x2f8/0x3b0
> [ 100.898439] __primary_switched+0xbc/0xc4
>
> What I would do is:
>
> struct qdisc_size_table *stab;
>
> rcu_read_lock();
> stab = rcu_dereference(q->root->stab);
> taprio_update_queue_max_sdu(q, oper, stab);
> rcu_read_unlock();
>
>> oper->cycle_end_time = new_base_time;
>> end_time = new_base_time;
>> +
>> + update_open_gate_duration(next, oper, num_tc,
>> + new_gate_duration);
>> + taprio_update_queue_max_sdu(q, oper, stab);
>> }
>> }
>>
>> for (tc = 0; tc < num_tc; tc++) {
>> - if (next->gate_duration[tc] == oper->cycle_time)
>> + if (cycle_corr_active(oper->cycle_time_correction) &&
>> + (next->gate_mask & BIT(tc)))
>> + /* Set to the new base time, ensuring a smooth transition
>> + * to the new schedule when the next entry finishes.
>> + */
>> + next->gate_close_time[tc] = end_time;
>> + else if (next->gate_duration[tc] == oper->cycle_time)
>> next->gate_close_time[tc] = KTIME_MAX;
>> else
>> next->gate_close_time[tc] = ktime_add_ns(entry->end_time,
>> --
>> 2.25.1
>>
>

Will update, thanks.