Subject: Re: [EXT] Re: [v3,net-next 1/4] net: qos: introduce a gate control flow action

From: Vlad Buslov <[email-masked]>
Date: Thu, 23 Apr 2020 14:03:27 +0300

On Thu 23 Apr 2020 at 11:32, Po Liu <[email-masked]> wrote:
>> -----Original Message-----
>> From: Vlad Buslov <[email-masked]>
>> Sent: 2020年4月23日 15:43
>> To: Po Liu <[email-masked]>
>> Cc: Vlad Buslov <[email-masked]>; [email-masked]; linux-
>> [email-masked]; [email-masked];
>> [email-masked]; Claudiu Manoil <[email-masked]>;
>> Vladimir Oltean <[email-masked]>; Alexandru Marginean
>> <[email-masked]>; [email-masked];
>> [email-masked]; [email-masked]; [email-masked];
>> [email-masked]; [email-masked];
>> [email-masked]; [email-masked];
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>> Subject: Re: [EXT] Re: [v3,net-next 1/4] net: qos: introduce a gate control
>> flow action
>> 
>> Caution: EXT Email
>> 
>> On Thu 23 Apr 2020 at 06:14, Po Liu <[email-masked]> wrote:
>> > Hi Vlad Buslov,
>> >
>> >> -----Original Message-----
>> >> From: Vlad Buslov <[email-masked]>
>> >> Sent: 2020年4月22日 21:23
>> >> To: Po Liu <[email-masked]>
>> >> Cc: [email-masked]; [email-masked];
>> >> [email-masked]; [email-masked]; Claudiu Manoil
>> >> <[email-masked]>; Vladimir Oltean
>> <[email-masked]>;
>> >> Alexandru Marginean <[email-masked]>;
>> >> [email-masked]; [email-masked];
>> [email-masked];
>> >> [email-masked]; [email-masked]; [email-masked];
>> >> [email-masked]; [email-masked];
>> >> [email-masked]; [email-masked]; [email-masked];
>> >> [email-masked]; [email-masked];
>> [email-masked];
>> >> [email-masked]; [email-masked];
>> >> [email-masked]
>> >> Subject: [EXT] Re: [v3,net-next 1/4] net: qos: introduce a gate
>> >> control flow action
>> >>
>> >> Caution: EXT Email
>> >>
>> >> Hi Po,
>> >>
>> >> On Wed 22 Apr 2020 at 05:48, Po Liu <[email-masked]> wrote:
>> >> > Introduce a ingress frame gate control flow action.
>> >> > Tc gate action does the work like this:
>> >> > Assume there is a gate allow specified ingress frames can be passed
>> >> > at specific time slot, and be dropped at specific time slot. Tc
>> >> > filter chooses the ingress frames, and tc gate action would specify
>> >> > what slot does these frames can be passed to device and what time
>> >> > slot would be dropped.
>> >> > Tc gate action would provide an entry list to tell how much time
>> >> > gate keep open and how much time gate keep state close. Gate
>> action
>> >> > also assign a start time to tell when the entry list start. Then
>> >> > driver would repeat the gate entry list cyclically.
>> >> > For the software simulation, gate action requires the user assign a
>> >> > time clock type.
>> >> >
>> >> > Below is the setting example in user space. Tc filter a stream
>> >> > source ip address is 192.168.0.20 and gate action own two time
>> >> > slots. One is last 200ms gate open let frame pass another is last
>> >> > 100ms gate close let frames dropped. When the frames have passed
>> >> > total frames over
>> >> > 8000000 bytes, frames will be dropped in one 200000000ns time slot.
>> >> >
>> >> >> tc qdisc add dev eth0 ingress
>> >> >
>> >> >> tc filter add dev eth0 parent ffff: protocol ip \
>> >> >          flower src_ip 192.168.0.20 \
>> >> >          action gate index 2 clockid CLOCK_TAI \
>> >> >          sched-entry open 200000000 -1 8000000 \
>> >> >          sched-entry close 100000000 -1 -1
>> >> >
>> >> >> tc chain del dev eth0 ingress chain 0
>> >> >
>> >> > "sched-entry" follow the name taprio style. Gate state is
>> >> > "open"/"close". Follow with period nanosecond. Then next item is
>> >> > internal priority value means which ingress queue should put. "-1"
>> >> > means wildcard. The last value optional specifies the maximum
>> >> > number of MSDU octets that are permitted to pass the gate during
>> >> > the specified time interval.
>> >> > Base-time is not set will be 0 as default, as result start time
>> >> > would be ((N + 1) * cycletime) which is the minimal of future time.
>> >> >
>> >> > Below example shows filtering a stream with destination mac address
>> >> > is
>> >> > 10:00:80:00:00:00 and ip type is ICMP, follow the action gate. The
>> >> > gate action would run with one close time slot which means always
>> >> > keep
>> >> close.
>> >> > The time cycle is total 200000000ns. The base-time would calculate by:
>> >> >
>> >> >  1357000000000 + (N + 1) * cycletime
>> >> >
>> >> > When the total value is the future time, it will be the start time.
>> >> > The cycletime here would be 200000000ns for this case.
>> >> >
>> >> >> tc filter add dev eth0 parent ffff:  protocol ip \
>> >> >          flower skip_hw ip_proto icmp dst_mac 10:00:80:00:00:00 \
>> >> >          action gate index 12 base-time 1357000000000 \
>> >> >          sched-entry close 200000000 -1 -1 \
>> >> >          clockid CLOCK_TAI
>> >> >
>> >> > Signed-off-by: Po Liu <[email-masked]>
>> >> > ---
>> >> >  include/net/tc_act/tc_gate.h        |  54 +++
>> >> >  include/uapi/linux/pkt_cls.h        |   1 +
>> >> >  include/uapi/linux/tc_act/tc_gate.h |  47 ++
>> >> >  net/sched/Kconfig                   |  13 +
>> >> >  net/sched/Makefile                  |   1 +
>> >> >  net/sched/act_gate.c                | 647
>> ++++++++++++++++++++++++++++
>> >> >  6 files changed, 763 insertions(+)  create mode 100644
>> >> > include/net/tc_act/tc_gate.h  create mode 100644
>> >> > include/uapi/linux/tc_act/tc_gate.h
>> >> >  create mode 100644 net/sched/act_gate.c
>> >> >
>> >> > diff --git a/include/net/tc_act/tc_gate.h
>> >> > b/include/net/tc_act/tc_gate.h new file mode 100644 index
>> >> > 000000000000..b0ace55b2aaa
>> >> > --- /dev/null
>> >> > +++ b/include/net/tc_act/tc_gate.h
>> >> > @@ -0,0 +1,54 @@
>> >> > +/* SPDX-License-Identifier: GPL-2.0-or-later */
>> >> > +/* Copyright 2020 NXP */
>> >> > +
>> >> > +#ifndef __NET_TC_GATE_H
>> >> > +#define __NET_TC_GATE_H
>> >> > +
>> >> > +#include <net/act_api.h>
>> >> > +#include <linux/tc_act/tc_gate.h>
>> >> > +
>> >> > +struct tcfg_gate_entry {
>> >> > +     int                     index;
>> >> > +     u8                      gate_state;
>> >> > +     u32                     interval;
>> >> > +     s32                     ipv;
>> >> > +     s32                     maxoctets;
>> >> > +     struct list_head        list;
>> >> > +};
>> >> > +
>> >> > +struct tcf_gate_params {
>> >> > +     s32                     tcfg_priority;
>> >> > +     u64                     tcfg_basetime;
>> >> > +     u64                     tcfg_cycletime;
>> >> > +     u64                     tcfg_cycletime_ext;
>> >> > +     u32                     tcfg_flags;
>> >> > +     s32                     tcfg_clockid;
>> >> > +     size_t                  num_entries;
>> >> > +     struct list_head        entries;
>> >> > +};
>> >> > +
>> >> > +#define GATE_ACT_GATE_OPEN   BIT(0)
>> >> > +#define GATE_ACT_PENDING     BIT(1)
>> >> > +struct gate_action {
>> >> > +     struct tcf_gate_params param;
>> >> > +     spinlock_t entry_lock;
>> >> > +     u8 current_gate_status;
>> >> > +     ktime_t current_close_time;
>> >> > +     u32 current_entry_octets;
>> >> > +     s32 current_max_octets;
>> >> > +     struct tcfg_gate_entry __rcu *next_entry;
>> >> > +     struct hrtimer hitimer;
>> >> > +     enum tk_offsets tk_offset;
>> >> > +     struct rcu_head rcu;
>> >> > +};
>> >> > +
>> >> > +struct tcf_gate {
>> >> > +     struct tc_action                common;
>> >> > +     struct gate_action __rcu        *actg;
>> >> > +};
>> >> > +#define to_gate(a) ((struct tcf_gate *)a)
>> >> > +
>> >> > +#define get_gate_param(act) ((struct tcf_gate_params *)act)
>> >> > +#define
>> >> > +get_gate_action(p) ((struct gate_action *)p)
>> >> > +
>> >> > +#endif
>> >> > diff --git a/include/uapi/linux/pkt_cls.h
>> >> > b/include/uapi/linux/pkt_cls.h index 9f06d29cab70..fc672b232437
>> >> 100644
>> >> > --- a/include/uapi/linux/pkt_cls.h
>> >> > +++ b/include/uapi/linux/pkt_cls.h
>> >> > @@ -134,6 +134,7 @@ enum tca_id {
>> >> >       TCA_ID_CTINFO,
>> >> >       TCA_ID_MPLS,
>> >> >       TCA_ID_CT,
>> >> > +     TCA_ID_GATE,
>> >> >       /* other actions go here */
>> >> >       __TCA_ID_MAX = 255
>> >> >  };
>> >> > diff --git a/include/uapi/linux/tc_act/tc_gate.h
>> >> > b/include/uapi/linux/tc_act/tc_gate.h
>> >> > new file mode 100644
>> >> > index 000000000000..f214b3a6d44f
>> >> > --- /dev/null
>> >> > +++ b/include/uapi/linux/tc_act/tc_gate.h
>> >> > @@ -0,0 +1,47 @@
>> >> > +/* SPDX-License-Identifier: GPL-2.0+ WITH Linux-syscall-note */
>> >> > +/* Copyright 2020 NXP */
>> >> > +
>> >> > +#ifndef __LINUX_TC_GATE_H
>> >> > +#define __LINUX_TC_GATE_H
>> >> > +
>> >> > +#include <linux/pkt_cls.h>
>> >> > +
>> >> > +struct tc_gate {
>> >> > +     tc_gen;
>> >> > +};
>> >> > +
>> >> > +enum {
>> >> > +     TCA_GATE_ENTRY_UNSPEC,
>> >> > +     TCA_GATE_ENTRY_INDEX,
>> >> > +     TCA_GATE_ENTRY_GATE,
>> >> > +     TCA_GATE_ENTRY_INTERVAL,
>> >> > +     TCA_GATE_ENTRY_IPV,
>> >> > +     TCA_GATE_ENTRY_MAX_OCTETS,
>> >> > +     __TCA_GATE_ENTRY_MAX,
>> >> > +};
>> >> > +#define TCA_GATE_ENTRY_MAX (__TCA_GATE_ENTRY_MAX - 1)
>> >> > +
>> >> > +enum {
>> >> > +     TCA_GATE_ONE_ENTRY_UNSPEC,
>> >> > +     TCA_GATE_ONE_ENTRY,
>> >> > +     __TCA_GATE_ONE_ENTRY_MAX,
>> >> > +};
>> >> > +#define TCA_GATE_ONE_ENTRY_MAX
>> (__TCA_GATE_ONE_ENTRY_MAX
>> >> - 1)
>> >> > +
>> >> > +enum {
>> >> > +     TCA_GATE_UNSPEC,
>> >> > +     TCA_GATE_TM,
>> >> > +     TCA_GATE_PARMS,
>> >> > +     TCA_GATE_PAD,
>> >> > +     TCA_GATE_PRIORITY,
>> >> > +     TCA_GATE_ENTRY_LIST,
>> >> > +     TCA_GATE_BASE_TIME,
>> >> > +     TCA_GATE_CYCLE_TIME,
>> >> > +     TCA_GATE_CYCLE_TIME_EXT,
>> >> > +     TCA_GATE_FLAGS,
>> >> > +     TCA_GATE_CLOCKID,
>> >> > +     __TCA_GATE_MAX,
>> >> > +};
>> >> > +#define TCA_GATE_MAX (__TCA_GATE_MAX - 1)
>> >> > +
>> >> > +#endif
>> >> > diff --git a/net/sched/Kconfig b/net/sched/Kconfig index
>> >> > bfbefb7bff9d..1314549c7567 100644
>> >> > --- a/net/sched/Kconfig
>> >> > +++ b/net/sched/Kconfig
>> >> > @@ -981,6 +981,19 @@ config NET_ACT_CT
>> >> >         To compile this code as a module, choose M here: the
>> >> >         module will be called act_ct.
>> >> >
>> >> > +config NET_ACT_GATE
>> >> > +     tristate "Frame gate entry list control tc action"
>> >> > +     depends on NET_CLS_ACT
>> >> > +     help
>> >> > +       Say Y here to allow to control the ingress flow to be passed at
>> >> > +       specific time slot and be dropped at other specific time slot by
>> >> > +       the gate entry list. The manipulation will simulate the IEEE
>> >> > +       802.1Qci stream gate control behavior.
>> >> > +
>> >> > +       If unsure, say N.
>> >> > +       To compile this code as a module, choose M here: the
>> >> > +       module will be called act_gate.
>> >> > +
>> >> >  config NET_IFE_SKBMARK
>> >> >       tristate "Support to encoding decoding skb mark on IFE action"
>> >> >       depends on NET_ACT_IFE
>> >> > diff --git a/net/sched/Makefile b/net/sched/Makefile index
>> >> > 31c367a6cd09..66bbf9a98f9e 100644
>> >> > --- a/net/sched/Makefile
>> >> > +++ b/net/sched/Makefile
>> >> > @@ -30,6 +30,7 @@ obj-$(CONFIG_NET_IFE_SKBPRIO)       +=
>> >> act_meta_skbprio.o
>> >> >  obj-$(CONFIG_NET_IFE_SKBTCINDEX)     += act_meta_skbtcindex.o
>> >> >  obj-$(CONFIG_NET_ACT_TUNNEL_KEY)+= act_tunnel_key.o
>> >> >  obj-$(CONFIG_NET_ACT_CT)     += act_ct.o
>> >> > +obj-$(CONFIG_NET_ACT_GATE)   += act_gate.o
>> >> >  obj-$(CONFIG_NET_SCH_FIFO)   += sch_fifo.o
>> >> >  obj-$(CONFIG_NET_SCH_CBQ)    += sch_cbq.o
>> >> >  obj-$(CONFIG_NET_SCH_HTB)    += sch_htb.o
>> >> > diff --git a/net/sched/act_gate.c b/net/sched/act_gate.c new file
>> >> > mode
>> >> > 100644 index 000000000000..e932f402b4f1
>> >> > --- /dev/null
>> >> > +++ b/net/sched/act_gate.c
>> >> > @@ -0,0 +1,647 @@
>> >> > +// SPDX-License-Identifier: GPL-2.0-or-later
>> >> > +/* Copyright 2020 NXP */
>> >> > +
>> >> > +#include <linux/module.h>
>> >> > +#include <linux/types.h>
>> >> > +#include <linux/kernel.h>
>> >> > +#include <linux/string.h>
>> >> > +#include <linux/errno.h>
>> >> > +#include <linux/skbuff.h>
>> >> > +#include <linux/rtnetlink.h>
>> >> > +#include <linux/init.h>
>> >> > +#include <linux/slab.h>
>> >> > +#include <net/act_api.h>
>> >> > +#include <net/netlink.h>
>> >> > +#include <net/pkt_cls.h>
>> >> > +#include <net/tc_act/tc_gate.h>
>> >> > +
>> >> > +static unsigned int gate_net_id;
>> >> > +static struct tc_action_ops act_gate_ops;
>> >> > +
>> >> > +static ktime_t gate_get_time(struct gate_action *gact) {
>> >> > +     ktime_t mono = ktime_get();
>> >> > +
>> >> > +     switch (gact->tk_offset) {
>> >> > +     case TK_OFFS_MAX:
>> >> > +             return mono;
>> >> > +     default:
>> >> > +             return ktime_mono_to_any(mono, gact->tk_offset);
>> >> > +     }
>> >> > +
>> >> > +     return KTIME_MAX;
>> >> > +}
>> >> > +
>> >> > +static int gate_get_start_time(struct gate_action *gact, ktime_t
>> >> > +*start) {
>> >> > +     struct tcf_gate_params *param = get_gate_param(gact);
>> >> > +     ktime_t now, base, cycle;
>> >> > +     u64 n;
>> >> > +
>> >> > +     base = ns_to_ktime(param->tcfg_basetime);
>> >> > +     now = gate_get_time(gact);
>> >> > +
>> >> > +     if (ktime_after(base, now)) {
>> >> > +             *start = base;
>> >> > +             return 0;
>> >> > +     }
>> >> > +
>> >> > +     cycle = param->tcfg_cycletime;
>> >> > +
>> >> > +     /* cycle time should not be zero */
>> >> > +     if (WARN_ON(!cycle))
>> >> > +             return -EFAULT;
>> >>
>> >> Looking at the init code it seems that this value can be set to 0
>> >> directly from netlink packet without further validation, which would
>> >> allow user to trigger warning here.
>> >
>> > Yes,  will avoid at ahead point.
>> >
>> >>
>> >> > +
>> >> > +     n = div64_u64(ktime_sub_ns(now, base), cycle);
>> >> > +     *start = ktime_add_ns(base, (n + 1) * cycle);
>> >> > +     return 0;
>> >> > +}
>> >> > +
>> >> > +static void gate_start_timer(struct gate_action *gact, ktime_t
>> >> > +start) {
>> >> > +     ktime_t expires;
>> >> > +
>> >> > +     expires = hrtimer_get_expires(&gact->hitimer);
>> >> > +     if (expires == 0)
>> >> > +             expires = KTIME_MAX;
>> >> > +
>> >> > +     start = min_t(ktime_t, start, expires);
>> >> > +
>> >> > +     hrtimer_start(&gact->hitimer, start, HRTIMER_MODE_ABS); }
>> >> > +
>> >> > +static enum hrtimer_restart gate_timer_func(struct hrtimer *timer) {
>> >> > +     struct gate_action *gact = container_of(timer, struct gate_action,
>> >> > +                                             hitimer);
>> >> > +     struct tcf_gate_params *p = get_gate_param(gact);
>> >> > +     struct tcfg_gate_entry *next;
>> >> > +     ktime_t close_time, now;
>> >> > +
>> >> > +     spin_lock(&gact->entry_lock);
>> >> > +
>> >> > +     next = rcu_dereference_protected(gact->next_entry,
>> >> > +
>> >> > + lockdep_is_held(&gact->entry_lock));
>> >> > +
>> >> > +     /* cycle start, clear pending bit, clear total octets */
>> >> > +     gact->current_gate_status = next->gate_state ?
>> >> GATE_ACT_GATE_OPEN : 0;
>> >> > +     gact->current_entry_octets = 0;
>> >> > +     gact->current_max_octets = next->maxoctets;
>> >> > +
>> >> > +     gact->current_close_time = ktime_add_ns(gact-
>> >current_close_time,
>> >> > +                                             next->interval);
>> >> > +
>> >> > +     close_time = gact->current_close_time;
>> >> > +
>> >> > +     if (list_is_last(&next->list, &p->entries))
>> >> > +             next = list_first_entry(&p->entries,
>> >> > +                                     struct tcfg_gate_entry, list);
>> >> > +     else
>> >> > +             next = list_next_entry(next, list);
>> >> > +
>> >> > +     now = gate_get_time(gact);
>> >> > +
>> >> > +     if (ktime_after(now, close_time)) {
>> >> > +             ktime_t cycle, base;
>> >> > +             u64 n;
>> >> > +
>> >> > +             cycle = p->tcfg_cycletime;
>> >> > +             base = ns_to_ktime(p->tcfg_basetime);
>> >> > +             n = div64_u64(ktime_sub_ns(now, base), cycle);
>> >> > +             close_time = ktime_add_ns(base, (n + 1) * cycle);
>> >> > +     }
>> >> > +
>> >> > +     rcu_assign_pointer(gact->next_entry, next);
>> >> > +     spin_unlock(&gact->entry_lock);
>> >>
>> >> I have couple of question about synchronization here:
>> >>
>> >> - Why do you need next_entry to be rcu pointer? It is only assigned
>> >> here with entry_lock protection and in init code before action is
>> >> visible to concurrent users. I don't see any unlocked rcu-protected
>> >> readers here that could benefit from it.
>> >>
>> >> - Why create dedicated entry_lock instead of using already existing
>> >> per- action tcf_lock?
>> >
>> > Will try to use the tcf_lock for verification.
>> > The thoughts came from that the timer period arrived then check
>> > through the list and then update next time would take much more time.
>> > Action function would be busy when traffic. So use a separate lock
>> > here for
>> >
>> >>
>> >> > +
>> >> > +     hrtimer_set_expires(&gact->hitimer, close_time);
>> >> > +
>> >> > +     return HRTIMER_RESTART;
>> >> > +}
>> >> > +
>> >> > +static int tcf_gate_act(struct sk_buff *skb, const struct tc_action *a,
>> >> > +                     struct tcf_result *res) {
>> >> > +     struct tcf_gate *g = to_gate(a);
>> >> > +     struct gate_action *gact;
>> >> > +     int action;
>> >> > +
>> >> > +     tcf_lastuse_update(&g->tcf_tm);
>> >> > +     bstats_cpu_update(this_cpu_ptr(g->common.cpu_bstats), skb);
>> >> > +
>> >> > +     action = READ_ONCE(g->tcf_action);
>> >> > +     rcu_read_lock();
>> >>
>> >> Action fastpath is already rcu read lock protected, you don't need to
>> >> manually obtain it.
>> >
>> > Will be removed.
>> >
>> >>
>> >> > +     gact = rcu_dereference_bh(g->actg);
>> >> > +     if (unlikely(gact->current_gate_status & GATE_ACT_PENDING)) {
>> >>
>> >> Can't current_gate_status be concurrently modified by timer callback?
>> >> This function doesn't use entry_lock to synchronize with timer.
>> >
>> > Will try tcf_lock either.
>> >
>> >>
>> >> > +             rcu_read_unlock();
>> >> > +             return action;
>> >> > +     }
>> >> > +
>> >> > +     if (!(gact->current_gate_status & GATE_ACT_GATE_OPEN))
>> >>
>> >> ...and here
>> >>
>> >> > +             goto drop;
>> >> > +
>> >> > +     if (gact->current_max_octets >= 0) {
>> >> > +             gact->current_entry_octets += qdisc_pkt_len(skb);
>> >> > +             if (gact->current_entry_octets >
>> >> > + gact->current_max_octets) {
>> >>
>> >> here also.
>> >>
>> >> > +
>> >> > + qstats_overlimit_inc(this_cpu_ptr(g->common.cpu_qstats));
>> >>
>> >> Please use tcf_action_inc_overlimit_qstats() and other wrappers for
>> stats.
>> >> Otherwise it will crash if user passes
>> TCA_ACT_FLAGS_NO_PERCPU_STATS
>> >> flag.
>> >
>> > The tcf_action_inc_overlimit_qstats() can't show limit counts in tc show
>> command. Is there anything need to do?
>> 
>> What do you mean? Internally tcf_action_inc_overlimit_qstats() just calls
>> qstats_overlimit_inc, if cpu_qstats percpu counter is not NULL:
>> 
>> 
>>         if (likely(a->cpu_qstats)) {
>>                 qstats_overlimit_inc(this_cpu_ptr(a->cpu_qstats));
>>                 return;
>>         }
>> 
>> Is there a subtle bug somewhere in this function?
>
> Sorry, I updated using the tcf_action_*, and the counting is ok. I moved back to the qstats_overlimit_inc() because tcf_action_* () include the spin_lock(&a->tcfa_lock). 
> I would update to  tcf_action_* () increate. 

BTW if you end up with synchronizing fastpath with tcfa_lock, then you
don't need to use tcf_action_*stats() helpers and percpu counters (they
will only slow down action init and increase memory usage without
providing any improvements for parallelism). Instead, you can just
directly change the tcf_{q|b}stats while holding the tcfa_lock. Check
pedit for example of such action.

>> > Br,
>> > Po Liu
> Thanks a lot.
> Br,
> Po Liu