DPDK: Data Plane Development Kit

18.02.0-rc0
rte_red.h File Reference
#include <stdint.h>
#include <limits.h>
#include <rte_common.h>
#include <rte_debug.h>
#include <rte_cycles.h>
#include <rte_branch_prediction.h>

Go to the source code of this file.

Data Structures

struct  rte_red_params
struct  rte_red_config
struct  rte_red

Macros

#define RTE_RED_SCALING   10
#define RTE_RED_S   (1 << 22)
#define RTE_RED_MAX_TH_MAX   1023
#define RTE_RED_WQ_LOG2_MIN   1
#define RTE_RED_WQ_LOG2_MAX   12
#define RTE_RED_MAXP_INV_MIN   1
#define RTE_RED_MAXP_INV_MAX   255
#define RTE_RED_2POW16   (1<<16)

Functions

int rte_red_rt_data_init (struct rte_red *red)
 Initialises run-time data.
int rte_red_config_init (struct rte_red_config *red_cfg, const uint16_t wq_log2, const uint16_t min_th, const uint16_t max_th, const uint16_t maxp_inv)
 Configures a single RED configuration parameter structure.
static uint32_t rte_fast_rand (void)
 Generate random number for RED.
static uint16_t __rte_red_calc_qempty_factor (uint8_t wq_log2, uint16_t m)
 calculate factor to scale average queue size when queue becomes empty
static int rte_red_enqueue_empty (const struct rte_red_config *red_cfg, struct rte_red *red, const uint64_t time)
 Updates queue average in condition when queue is empty.
static int __rte_red_drop (const struct rte_red_config *red_cfg, struct rte_red *red)
 make a decision to drop or enqueue a packet based on mark probability criteria
static int rte_red_enqueue_nonempty (const struct rte_red_config *red_cfg, struct rte_red *red, const unsigned q)
 Decides if new packet should be enqeued or dropped in queue non-empty case.
static int rte_red_enqueue (const struct rte_red_config *red_cfg, struct rte_red *red, const unsigned q, const uint64_t time)
 Decides if new packet should be enqeued or dropped Updates run time data based on new queue size value. Based on new queue average and RED configuration parameters gives verdict whether to enqueue or drop the packet.
static void rte_red_mark_queue_empty (struct rte_red *red, const uint64_t time)
 Callback to records time that queue became empty.

Variables

uint32_t rte_red_rand_val

Detailed Description

RTE Random Early Detection (RED)

Definition in file rte_red.h.

Macro Definition Documentation

#define RTE_RED_SCALING   10

Fraction size for fixed-point

Definition at line 55 of file rte_red.h.

#define RTE_RED_S   (1 << 22)

Packet size multiplied by number of leaf queues

Definition at line 56 of file rte_red.h.

#define RTE_RED_MAX_TH_MAX   1023

Max threshold limit in fixed point format

Definition at line 57 of file rte_red.h.

#define RTE_RED_WQ_LOG2_MIN   1

Min inverse filter weight value

Definition at line 58 of file rte_red.h.

#define RTE_RED_WQ_LOG2_MAX   12

Max inverse filter weight value

Definition at line 59 of file rte_red.h.

#define RTE_RED_MAXP_INV_MIN   1

Min inverse mark probability value

Definition at line 60 of file rte_red.h.

#define RTE_RED_MAXP_INV_MAX   255

Max inverse mark probability value

Definition at line 61 of file rte_red.h.

#define RTE_RED_2POW16   (1<<16)

2 power 16

Definition at line 62 of file rte_red.h.

Function Documentation

int rte_red_rt_data_init ( struct rte_red red)

Initialises run-time data.

Parameters
red[in,out] data pointer to RED runtime data
Returns
Operation status
Return values
0success
!0error
int rte_red_config_init ( struct rte_red_config red_cfg,
const uint16_t  wq_log2,
const uint16_t  min_th,
const uint16_t  max_th,
const uint16_t  maxp_inv 
)

Configures a single RED configuration parameter structure.

Parameters
red_cfg[in,out] config pointer to a RED configuration parameter structure
wq_log2[in] log2 of the filter weight, valid range is: RTE_RED_WQ_LOG2_MIN <= wq_log2 <= RTE_RED_WQ_LOG2_MAX
min_th[in] queue minimum threshold in number of packets
max_th[in] queue maximum threshold in number of packets
maxp_inv[in] inverse maximum mark probability
Returns
Operation status
Return values
0success
!0error
static uint32_t rte_fast_rand ( void  )
inlinestatic

Generate random number for RED.

Implementation based on: http://software.intel.com/en-us/articles/fast-random-number-generator-on-the-intel-pentiumr-4-processor/

10 bit shift has been found through empirical tests (was 16).

Returns
Random number between 0 and (2^22 - 1)

Definition at line 150 of file rte_red.h.

static uint16_t __rte_red_calc_qempty_factor ( uint8_t  wq_log2,
uint16_t  m 
)
inlinestatic

calculate factor to scale average queue size when queue becomes empty

Parameters
wq_log2[in] where EWMA filter weight wq = 1/(2 ^ wq_log2)
m[in] exponent in the computed value (1 - wq) ^ m
Returns
computed value
Return values
((1- wq) ^ m) scaled in fixed-point format

Basic math tells us that: a^b = 2^(b * log2(a) )

in our case: a = (1-Wq) b = m Wq = 1/ (2^log2n)

So we are computing this equation: factor = 2 ^ ( m * log2(1-Wq))

First we are computing: n = m * log2(1-Wq)

To avoid dealing with signed numbers log2 values are positive but they should be negative because (1-Wq) is always < 1. Contents of log2 table values are also scaled for precision.

The tricky part is computing 2^n, for this I split n into integer part and fraction part. f - is fraction part of n n - is integer part of original n

Now using basic math we compute 2^n: 2^(f+n) = 2^f * 2^n 2^f - we use lookup table 2^n - can be replaced with bit shift right operations

Definition at line 167 of file rte_red.h.

static int rte_red_enqueue_empty ( const struct rte_red_config red_cfg,
struct rte_red red,
const uint64_t  time 
)
inlinestatic

Updates queue average in condition when queue is empty.

Note: packet is never dropped in this particular case.

Parameters
red_cfg[in] config pointer to a RED configuration parameter structure
red[in,out] data pointer to RED runtime data
time[in] current time stamp
Returns
Operation status
Return values
0enqueue the packet
1drop the packet based on max threshold criterion
2drop the packet based on mark probability criterion

We compute avg but we don't compare avg against min_th or max_th, nor calculate drop probability

m is the number of packets that might have arrived while the queue was empty. In this case we have time stamps provided by scheduler in byte units (bytes transmitted on network port). Such time stamp translates into time units as port speed is fixed but such approach simplifies the code.

Check that m will fit into 16-bit unsigned integer

Definition at line 230 of file rte_red.h.

static int __rte_red_drop ( const struct rte_red_config red_cfg,
struct rte_red red 
)
inlinestatic

make a decision to drop or enqueue a packet based on mark probability criteria

Drop probability (Sally Floyd and Van Jacobson):

pb = (1 / maxp_inv) * (avg - min_th) / (max_th - min_th) pa = pb / (2 - count * pb)

        (1 / maxp_inv) * (avg - min_th)
       ---------------------------------
                max_th - min_th

pa = -----------------------------------------—— count * (1 / maxp_inv) * (avg - min_th) 2 - -----------------------------------—— max_th - min_th

    avg - min_th

pa = -----------------------------------------------------—— 2 * (max_th - min_th) * maxp_inv - count * (avg - min_th)

We define pa_const as: pa_const = 2 * (max_th - min_th) * maxp_inv. Then:

               avg - min_th

pa = -----------------------------—— pa_const - count * (avg - min_th)

Parameters
red_cfg[in] config pointer to structure defining RED parameters
red[in,out] data pointer to RED runtime data
Returns
operation status
Return values
0enqueue the packet
1drop the packet

Definition at line 308 of file rte_red.h.

static int rte_red_enqueue_nonempty ( const struct rte_red_config red_cfg,
struct rte_red red,
const unsigned  q 
)
inlinestatic

Decides if new packet should be enqeued or dropped in queue non-empty case.

Parameters
red_cfg[in] config pointer to a RED configuration parameter structure
red[in,out] data pointer to RED runtime data
q[in] current queue size (measured in packets)
Returns
Operation status
Return values
0enqueue the packet
1drop the packet based on max threshold criterion
2drop the packet based on mark probability criterion

EWMA filter (Sally Floyd and Van Jacobson): avg = (1 - wq) * avg + wq * q avg = avg + q * wq - avg * wq

We select: wq = 2^(-n). Let scaled version of avg be: avg_s = avg * 2^(N+n). We get: avg_s = avg_s + q * 2^N - avg_s * 2^(-n)

By using shift left/right operations, we get: avg_s = avg_s + (q << N) - (avg_s >> n) avg_s += (q << N) - (avg_s >> n)

Definition at line 347 of file rte_red.h.

static int rte_red_enqueue ( const struct rte_red_config red_cfg,
struct rte_red red,
const unsigned  q,
const uint64_t  time 
)
inlinestatic

Decides if new packet should be enqeued or dropped Updates run time data based on new queue size value. Based on new queue average and RED configuration parameters gives verdict whether to enqueue or drop the packet.

Parameters
red_cfg[in] config pointer to a RED configuration parameter structure
red[in,out] data pointer to RED runtime data
q[in] updated queue size in packets
time[in] current time stamp
Returns
Operation status
Return values
0enqueue the packet
1drop the packet based on max threshold criteria
2drop the packet based on mark probability criteria

Definition at line 409 of file rte_red.h.

static void rte_red_mark_queue_empty ( struct rte_red red,
const uint64_t  time 
)
inlinestatic

Callback to records time that queue became empty.

Parameters
red[in,out] data pointer to RED runtime data
time[in] current time stamp

Definition at line 431 of file rte_red.h.

Variable Documentation

uint32_t rte_red_rand_val

Externs