RE: [PATCH v3] sched: enable/disable TC OV at runtime

["Ajmera, Megha" <megha.ajmera@intel.com>]

Hi Cristian, Marcin,

> > -----Original Message-----
> > From: Danilewicz, MarcinX <marcinx.danilewicz@intel.com>
> > Sent: Wednesday, April 27, 2022 10:24 AM
> > To: dev@dpdk.org; Singh, Jasvinder <jasvinder.singh@intel.com>;
> > Dumitrescu, Cristian <cristian.dumitrescu@intel.com>
> > Cc: Ajmera, Megha <megha.ajmera@intel.com>
> > Subject: [PATCH v3] sched: enable/disable TC OV at runtime
> 
> We are not trying to enable/disable the traffic class oversubscription feature at
> run-time, but at initialization. If cat, we should prohibit changing this post-
> initialization.
>

If we only need this to be configured at initialization time, then we can as well take this flag in subport config API itself. Then there will be no need for a new API. The purpose of new API was to enable/disable this feature at runtime.
 
> Also the name of the feature should not be abbreviated in the patch title.
> 
> I suggest you rework the title to:
> [PATCH] sched: enable traffic class oversubscription conditionally
> 
> >
> > Added new API to enable or disable TC over subscription for best
> > effort traffic class at subport level.
> > Added changes after review and increased throughput.
> >
> > By default TC OV is disabled.
> 
> It should be the other way around, the TC_OV should be enabled by default. The
> TC oversubscription is a more natural way to use this library, we usually want to
> disable this feature just for better performance in case this functionality is not
> needed. Please initialize the tc_ov flag accordingly.
>

In original code, this feature has always been disabled as it impacts performance.
So, in my opinion we should keep it disabled by default and let user enable it when required.
 
> >
> > Signed-off-by: Marcin Danilewicz <marcinx.danilewicz@intel.com>
> > ---
> >  lib/sched/rte_sched.c | 189
> > +++++++++++++++++++++++++++++++++++-------
> >  lib/sched/rte_sched.h |  18 ++++
> >  lib/sched/version.map |   3 +
> >  3 files changed, 178 insertions(+), 32 deletions(-)
> >
> > diff --git a/lib/sched/rte_sched.c b/lib/sched/rte_sched.c index
> > ec74bee939..6e7d81df46 100644
> > --- a/lib/sched/rte_sched.c
> > +++ b/lib/sched/rte_sched.c
> > @@ -213,6 +213,9 @@ struct rte_sched_subport {
> >  	uint8_t *bmp_array;
> >  	struct rte_mbuf **queue_array;
> >  	uint8_t memory[0] __rte_cache_aligned;
> > +
> > +	/* TC oversubscription activation */
> > +	int is_tc_ov_enabled;
> 
> How about we simplify the name of this variable to: tc_ov_enabled ?
> 
> >  } __rte_cache_aligned;
> >
> >  struct rte_sched_port {
> > @@ -1165,6 +1168,45 @@ rte_sched_cman_config(struct rte_sched_port
> > *port,  }  #endif
> >
> > +int
> > +rte_sched_subport_tc_ov_config(struct rte_sched_port *port,
> > +	uint32_t subport_id,
> > +	bool tc_ov_enable)
> > +{
> > +	struct rte_sched_subport *s;
> > +	struct rte_sched_subport_profile *profile;
> > +
> > +	if (port == NULL) {
> > +		RTE_LOG(ERR, SCHED,
> > +			"%s: Incorrect value for parameter port\n", __func__);
> > +		return -EINVAL;
> > +	}
> > +
> > +	if (subport_id >= port->n_subports_per_port) {
> > +		RTE_LOG(ERR, SCHED,
> > +			"%s: Incorrect value for parameter subport id\n",
> > __func__);
> > +		return  -EINVAL;
> > +	}
> > +
> > +	s = port->subports[subport_id];
> > +	s->is_tc_ov_enabled = tc_ov_enable ? 1 : 0;
> > +
> > +	if (s->is_tc_ov_enabled) {
> > +		/* TC oversubscription */
> > +		s->tc_ov_wm_min = port->mtu;
> > +		s->tc_ov_period_id = 0;
> > +		s->tc_ov = 0;
> > +		s->tc_ov_n = 0;
> > +		s->tc_ov_rate = 0;
> > +
> > +		profile = port->subport_profiles + s->profile;
> > +		s->tc_ov_wm_max = rte_sched_time_ms_to_bytes(profile-
> > >tc_period,
> > +				s->pipe_tc_be_rate_max);
> > +		s->tc_ov_wm = s->tc_ov_wm_max;
> > +	}
> > +	return 0;
> > +}
> 
> This function should not exist, please remove it and keep the initial code that
> computes the tc_ov related variable regardless of whether tc_ov is enabled or
> not.
> 
> All the tc_ov related variables have the tc_ov particle in their name, so there is
> no clash. This is initialization code, so no performance overhead. Let's keep the
> code unmodified and compute both the tc_ov and the non-tc_ov varables at
> initialization, regardless of whether the feature is enabled or not.
> 
> This comment is applicable to all the initialization code, please adjust all the init
> code accordingly. There should be no diff showing in the patch for any of the init
> code!
> 
> For this file "rte_sched.c", your patch should contain just two additional run-
> time functions, i.e. the non-tc-ov version of functions grinder_credits_update()
> and grindler_credits_check(), and the small code required to test when to use
> the tc-ov vs. the non-tc_ov version, makes sense?
> 
> > +
> >  int
> >  is_tc_ov_enabled (struct rte_sched_port *port,
> >  	uint32_t subport_id,
> > @@ -1254,6 +1296,9 @@ rte_sched_subport_config(struct rte_sched_port
> > *port,
> >  		s->n_pipe_profiles = params->n_pipe_profiles;
> >  		s->n_max_pipe_profiles = params->n_max_pipe_profiles;
> >
> > +		/* TC over-subscription is disabled by default */
> > +		s->is_tc_ov_enabled = 0;
> > +
> 
> By default, this feature should be enabled:
> s->is_tc_ov_enabled = 1;
> 
> >  #ifdef RTE_SCHED_CMAN
> >  		if (params->cman_params != NULL) {
> >  			s->cman_enabled = true;
> > @@ -1316,13 +1361,6 @@ rte_sched_subport_config(struct rte_sched_port
> > *port,
> >
> >  		for (i = 0; i < RTE_SCHED_PORT_N_GRINDERS; i++)
> >  			s->grinder_base_bmp_pos[i] =
> > RTE_SCHED_PIPE_INVALID;
> > -
> > -		/* TC oversubscription */
> > -		s->tc_ov_wm_min = port->mtu;
> > -		s->tc_ov_period_id = 0;
> > -		s->tc_ov = 0;
> > -		s->tc_ov_n = 0;
> > -		s->tc_ov_rate = 0;
> >  	}
> >
> >  	{
> > @@ -1342,9 +1380,6 @@ rte_sched_subport_config(struct rte_sched_port
> > *port,
> >  			else
> >  				profile->tc_credits_per_period[i] = 0;
> >
> > -		s->tc_ov_wm_max = rte_sched_time_ms_to_bytes(profile-
> > >tc_period,
> > -							s-
> > >pipe_tc_be_rate_max);
> > -		s->tc_ov_wm = s->tc_ov_wm_max;
> >  		s->profile = subport_profile_id;
> >
> >  	}
> > @@ -1417,17 +1452,20 @@ rte_sched_pipe_config(struct rte_sched_port
> > *port,
> >  		double pipe_tc_be_rate =
> >  			(double) params-
> > >tc_credits_per_period[RTE_SCHED_TRAFFIC_CLASS_BE]
> >  			/ (double) params->tc_period;
> > -		uint32_t tc_be_ov = s->tc_ov;
> >
> > -		/* Unplug pipe from its subport */
> > -		s->tc_ov_n -= params->tc_ov_weight;
> > -		s->tc_ov_rate -= pipe_tc_be_rate;
> > -		s->tc_ov = s->tc_ov_rate > subport_tc_be_rate;
> > +		if (s->is_tc_ov_enabled) {
> > +			uint32_t tc_be_ov = s->tc_ov;
> >
> > -		if (s->tc_ov != tc_be_ov) {
> > -			RTE_LOG(DEBUG, SCHED,
> > -				"Subport %u Best-effort TC oversubscription is
> > OFF (%.4lf >= %.4lf)\n",
> > -				subport_id, subport_tc_be_rate, s-
> > >tc_ov_rate);
> > +			/* Unplug pipe from its subport */
> > +			s->tc_ov_n -= params->tc_ov_weight;
> > +			s->tc_ov_rate -= pipe_tc_be_rate;
> > +			s->tc_ov = s->tc_ov_rate > subport_tc_be_rate;
> > +
> > +			if (s->tc_ov != tc_be_ov) {
> > +				RTE_LOG(DEBUG, SCHED,
> > +					"Subport %u Best-effort TC
> > oversubscription is OFF (%.4lf >= %.4lf)\n",
> > +					subport_id, subport_tc_be_rate, s-
> > >tc_ov_rate);
> > +			}
> >  		}
> >
> >  		/* Reset the pipe */
> > @@ -1460,19 +1498,22 @@ rte_sched_pipe_config(struct rte_sched_port
> > *port,
> >  		double pipe_tc_be_rate =
> >  			(double) params-
> > >tc_credits_per_period[RTE_SCHED_TRAFFIC_CLASS_BE]
> >  			/ (double) params->tc_period;
> > -		uint32_t tc_be_ov = s->tc_ov;
> >
> > -		s->tc_ov_n += params->tc_ov_weight;
> > -		s->tc_ov_rate += pipe_tc_be_rate;
> > -		s->tc_ov = s->tc_ov_rate > subport_tc_be_rate;
> > +		if (s->is_tc_ov_enabled) {
> > +			uint32_t tc_be_ov = s->tc_ov;
> > +
> > +			s->tc_ov_n += params->tc_ov_weight;
> > +			s->tc_ov_rate += pipe_tc_be_rate;
> > +			s->tc_ov = s->tc_ov_rate > subport_tc_be_rate;
> >
> > -		if (s->tc_ov != tc_be_ov) {
> > -			RTE_LOG(DEBUG, SCHED,
> > -				"Subport %u Best effort TC oversubscription is
> > ON (%.4lf < %.4lf)\n",
> > -				subport_id, subport_tc_be_rate, s-
> > >tc_ov_rate);
> > +			if (s->tc_ov != tc_be_ov) {
> > +				RTE_LOG(DEBUG, SCHED,
> > +					"Subport %u Best effort TC
> > oversubscription is ON (%.4lf < %.4lf)\n",
> > +					subport_id, subport_tc_be_rate, s-
> > >tc_ov_rate);
> > +			}
> > +			p->tc_ov_period_id = s->tc_ov_period_id;
> > +			p->tc_ov_credits = s->tc_ov_wm;
> >  		}
> > -		p->tc_ov_period_id = s->tc_ov_period_id;
> > -		p->tc_ov_credits = s->tc_ov_wm;
> >  	}
> >
> >  	return 0;
> > @@ -2318,6 +2359,45 @@ grinder_credits_update(struct rte_sched_port
> > *port,
> >  	pipe->tb_credits = RTE_MIN(pipe->tb_credits, params->tb_size);
> >  	pipe->tb_time += n_periods * params->tb_period;
> >
> > +	/* Subport TCs */
> > +	if (unlikely(port->time >= subport->tc_time)) {
> > +		for (i = 0; i < RTE_SCHED_TRAFFIC_CLASSES_PER_PIPE; i++)
> > +			subport->tc_credits[i] = sp->tc_credits_per_period[i];
> > +
> > +		subport->tc_time = port->time + sp->tc_period;
> > +	}
> > +
> > +	/* Pipe TCs */
> > +	if (unlikely(port->time >= pipe->tc_time)) {
> > +		for (i = 0; i < RTE_SCHED_TRAFFIC_CLASSES_PER_PIPE; i++)
> > +			pipe->tc_credits[i] = params->tc_credits_per_period[i];
> > +		pipe->tc_time = port->time + params->tc_period;
> > +	}
> > +}
> > +
> > +static inline void
> > +grinder_credits_update_with_tc_ov(struct rte_sched_port *port,
> > +	struct rte_sched_subport *subport, uint32_t pos) {
> > +	struct rte_sched_grinder *grinder = subport->grinder + pos;
> > +	struct rte_sched_pipe *pipe = grinder->pipe;
> > +	struct rte_sched_pipe_profile *params = grinder->pipe_params;
> > +	struct rte_sched_subport_profile *sp = grinder->subport_params;
> > +	uint64_t n_periods;
> > +	uint32_t i;
> > +
> > +	/* Subport TB */
> > +	n_periods = (port->time - subport->tb_time) / sp->tb_period;
> > +	subport->tb_credits += n_periods * sp->tb_credits_per_period;
> > +	subport->tb_credits = RTE_MIN(subport->tb_credits, sp->tb_size);
> > +	subport->tb_time += n_periods * sp->tb_period;
> > +
> > +	/* Pipe TB */
> > +	n_periods = (port->time - pipe->tb_time) / params->tb_period;
> > +	pipe->tb_credits += n_periods * params->tb_credits_per_period;
> > +	pipe->tb_credits = RTE_MIN(pipe->tb_credits, params->tb_size);
> > +	pipe->tb_time += n_periods * params->tb_period;
> > +
> >  	/* Subport TCs */
> >  	if (unlikely(port->time >= subport->tc_time)) {
> >  		subport->tc_ov_wm =
> > @@ -2348,6 +2428,39 @@ grinder_credits_update(struct rte_sched_port
> > *port,  static inline int  grinder_credits_check(struct rte_sched_port
> > *port,
> >  	struct rte_sched_subport *subport, uint32_t pos)
> > +{
> > +	struct rte_sched_grinder *grinder = subport->grinder + pos;
> > +	struct rte_sched_pipe *pipe = grinder->pipe;
> > +	struct rte_mbuf *pkt = grinder->pkt;
> > +	uint32_t tc_index = grinder->tc_index;
> > +	uint64_t pkt_len = pkt->pkt_len + port->frame_overhead;
> > +	uint64_t subport_tb_credits = subport->tb_credits;
> > +	uint64_t subport_tc_credits = subport->tc_credits[tc_index];
> > +	uint64_t pipe_tb_credits = pipe->tb_credits;
> > +	uint64_t pipe_tc_credits = pipe->tc_credits[tc_index];
> > +	int enough_credits;
> > +
> > +	/* Check pipe and subport credits */
> > +	enough_credits = (pkt_len <= subport_tb_credits) &&
> > +		(pkt_len <= subport_tc_credits) &&
> > +		(pkt_len <= pipe_tb_credits) &&
> > +		(pkt_len <= pipe_tc_credits);
> > +
> > +	if (!enough_credits)
> > +		return 0;
> > +
> > +	/* Update pipe and subport credits */
> > +	subport->tb_credits -= pkt_len;
> > +	subport->tc_credits[tc_index] -= pkt_len;
> > +	pipe->tb_credits -= pkt_len;
> > +	pipe->tc_credits[tc_index] -= pkt_len;
> > +
> > +	return 1;
> > +}
> > +
> > +static inline int
> > +grinder_credits_check_with_tc_ov(struct rte_sched_port *port,
> > +	struct rte_sched_subport *subport, uint32_t pos)
> >  {
> >  	struct rte_sched_grinder *grinder = subport->grinder + pos;
> >  	struct rte_sched_pipe *pipe = grinder->pipe; @@ -2403,8 +2516,16 @@
> > grinder_schedule(struct rte_sched_port *port,
> >  	uint32_t pkt_len = pkt->pkt_len + port->frame_overhead;
> >  	uint32_t be_tc_active;
> >
> > -	if (!grinder_credits_check(port, subport, pos))
> > -		return 0;
> > +	switch (subport->is_tc_ov_enabled) {
> > +	case 1:
> > +		if (!grinder_credits_check_with_tc_ov(port, subport, pos))
> > +			return 0;
> > +		break;
> > +	case 0:
> > +		if (!grinder_credits_check(port, subport, pos))
> > +			return 0;
> > +		break;
> > +	}
> 
> There should be no switch statement here, please replace with an if statement. I
> suggest the following:
> 
> int status;
> 
> status = subport->tc_ov_enabled ? grinder_credits_check_with_tc_ov(port,
> subport, pos) : grinder_credits_check(port, subport, pos); if (!status)
> 	return 0;
> 
> >
> >  	/* Advance port time */
> >  	port->time += pkt_len;
> > @@ -2770,7 +2891,11 @@ grinder_handle(struct rte_sched_port *port,
> >  						subport->profile;
> >
> >  		grinder_prefetch_tc_queue_arrays(subport, pos);
> > -		grinder_credits_update(port, subport, pos);
> > +
> > +		if (unlikely(subport->is_tc_ov_enabled))
> 
> Please remove the "unlikely" from here, don't put any likely/unlikely here at all.
> 
> > +			grinder_credits_update_with_tc_ov(port, subport, pos);
> > +		else
> > +			grinder_credits_update(port, subport, pos);
> >
> >  		grinder->state = e_GRINDER_PREFETCH_MBUF;
> >  		return 0;
> > diff --git a/lib/sched/rte_sched.h b/lib/sched/rte_sched.h index
> > 5ece64e527..94febe1d94 100644
> > --- a/lib/sched/rte_sched.h
> > +++ b/lib/sched/rte_sched.h
> > @@ -579,6 +579,24 @@ rte_sched_port_enqueue(struct rte_sched_port
> > *port, struct rte_mbuf **pkts, uint  int
> > rte_sched_port_dequeue(struct rte_sched_port *port, struct rte_mbuf
> > **pkts, uint32_t n_pkts);
> >
> > +/**
> > + * Hierarchical scheduler subport TC OV enable/disable config.
> 
> The name of the feature should be fully stated here: traffic class
> oversubscription, not the abbreviation, please change.
> 
> 
> > + * Note that this function is safe to use at runtime
> > + * to enable/disable TC OV for subport.
> 
> We should actually forbit this rather than encourage it. Calling this function
> several times does not make sense, and it can create limitations that can come
> back and byte us in the future, whenever we might need to extend this code, for
> no reason.
> 
> Please actually replace with: "This function should be called at the time of
> subport initialization."
> 
> > + *
> > + * @param port
> > + *   Handle to port scheduler instance
> > + * @param subport_id
> > + *   Subport ID
> > + * @param tc_ov_enable
> > + *  Boolean flag to enable/disable TC OV
> > + * @return
> > + *   0 upon success, error code otherwise
> > + */
> > +__rte_experimental
> > +int
> > +rte_sched_subport_tc_ov_config(struct rte_sched_port *port, uint32_t
> > subport_id, bool tc_ov_enable);
> > +
> >  #ifdef __cplusplus
> >  }
> >  #endif
> > diff --git a/lib/sched/version.map b/lib/sched/version.map index
> > d22c07fc9f..c6e994d8df 100644
> > --- a/lib/sched/version.map
> > +++ b/lib/sched/version.map
> > @@ -34,4 +34,7 @@ EXPERIMENTAL {
> >  	# added in 21.11
> >  	rte_pie_rt_data_init;
> >  	rte_pie_config_init;
> > +
> > +	# added in 22.03
> 
> This is not in 22.03, it will hopefully be in 22.07.
> 
> > +	rte_sched_subport_tc_ov_config;
> >  };
> > --
> > 2.25.1
> 
> Regards,
> Cristian