intrte_red_rt_data_init(structrte_red*red)
Initialises run-time data.
Parametersred [in,out] data pointer to RED runtime data
Returns
Operation status
Returnvalues0 success
!0 error
intrte_red_config_init(structrte_red_config*red_cfg,constuint16_twq_log2,constuint16_tmin_th,constuint16_tmax_th,constuint16_tmaxp_inv)
Configures a single RED configuration parameter structure.
Parametersred_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
Returnvalues0 success
!0 error
staticuint32_trte_fast_rand(void)[inline],[static]
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 116 of file rte_red.h.
staticuint16_t__rte_red_calc_qempty_factor(uint8_twq_log2,uint16_tm)[inline],[static]
calculate factor to scale average queue size when queue becomes empty
Parameterswq_log2 [in] where EWMA filter weight wq = 1/(2 ^ wq_log2)
m [in] exponent in the computed value (1 - wq) ^ m
Returns
computed value
Returnvalues((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 133 of file rte_red.h.
staticintrte_red_enqueue_empty(conststructrte_red_config*red_cfg,structrte_red*red,constuint64_ttime)[inline],[static]
Updates queue average in condition when queue is empty. Note: packet is never dropped in this particular
case.
Parametersred_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
Returnvalues0 enqueue the packet
1 drop the packet based on max threshold criterion
2 drop 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 196 of file rte_red.h.
staticint__rte_red_drop(conststructrte_red_config*red_cfg,structrte_red*red)[inline],[static]
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)
Parametersred_cfg [in] config pointer to structure defining RED parameters
red [in,out] data pointer to RED runtime data
Returns
operation status
Returnvalues0 enqueue the packet
1 drop the packet
Definition at line 274 of file rte_red.h.
staticintrte_red_enqueue_nonempty(conststructrte_red_config*red_cfg,structrte_red*red,constunsignedq)[inline],[static]
Decides if new packet should be enqueued or dropped in queue non-empty case.
Parametersred_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
Returnvalues0 enqueue the packet
1 drop the packet based on max threshold criterion
2 drop 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 313 of file rte_red.h.
staticintrte_red_enqueue(conststructrte_red_config*red_cfg,structrte_red*red,constunsignedq,constuint64_ttime)[inline],[static]
Decides if new packet should be enqueued 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.
Parametersred_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
Returnvalues0 enqueue the packet
1 drop the packet based on max threshold criteria
2 drop the packet based on mark probability criteria
Definition at line 375 of file rte_red.h.
staticvoidrte_red_mark_queue_empty(structrte_red*red,constuint64_ttime)[inline],[static]
Callback to records time that queue became empty.
Parametersred [in,out] data pointer to RED runtime data
time [in] current time stamp
Definition at line 397 of file rte_red.h.
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