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466 lines
11 KiB
466 lines
11 KiB
/* SPDX-License-Identifier: GPL-2.0 */ |
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#ifndef __NET_SCHED_RED_H |
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#define __NET_SCHED_RED_H |
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#include <linux/types.h> |
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#include <linux/bug.h> |
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#include <net/pkt_sched.h> |
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#include <net/inet_ecn.h> |
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#include <net/dsfield.h> |
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#include <linux/reciprocal_div.h> |
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/* Random Early Detection (RED) algorithm. |
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======================================= |
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Source: Sally Floyd and Van Jacobson, "Random Early Detection Gateways |
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for Congestion Avoidance", 1993, IEEE/ACM Transactions on Networking. |
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This file codes a "divisionless" version of RED algorithm |
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as written down in Fig.17 of the paper. |
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Short description. |
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------------------ |
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When a new packet arrives we calculate the average queue length: |
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avg = (1-W)*avg + W*current_queue_len, |
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W is the filter time constant (chosen as 2^(-Wlog)), it controls |
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the inertia of the algorithm. To allow larger bursts, W should be |
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decreased. |
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if (avg > th_max) -> packet marked (dropped). |
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if (avg < th_min) -> packet passes. |
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if (th_min < avg < th_max) we calculate probability: |
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Pb = max_P * (avg - th_min)/(th_max-th_min) |
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and mark (drop) packet with this probability. |
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Pb changes from 0 (at avg==th_min) to max_P (avg==th_max). |
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max_P should be small (not 1), usually 0.01..0.02 is good value. |
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max_P is chosen as a number, so that max_P/(th_max-th_min) |
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is a negative power of two in order arithmetics to contain |
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only shifts. |
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Parameters, settable by user: |
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----------------------------- |
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qth_min - bytes (should be < qth_max/2) |
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qth_max - bytes (should be at least 2*qth_min and less limit) |
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Wlog - bits (<32) log(1/W). |
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Plog - bits (<32) |
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Plog is related to max_P by formula: |
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max_P = (qth_max-qth_min)/2^Plog; |
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F.e. if qth_max=128K and qth_min=32K, then Plog=22 |
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corresponds to max_P=0.02 |
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Scell_log |
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Stab |
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Lookup table for log((1-W)^(t/t_ave). |
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NOTES: |
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Upper bound on W. |
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----------------- |
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If you want to allow bursts of L packets of size S, |
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you should choose W: |
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L + 1 - th_min/S < (1-(1-W)^L)/W |
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th_min/S = 32 th_min/S = 4 |
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log(W) L |
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-1 33 |
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-2 35 |
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-3 39 |
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-4 46 |
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-5 57 |
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-6 75 |
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-7 101 |
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-8 135 |
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-9 190 |
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etc. |
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*/ |
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/* |
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* Adaptative RED : An Algorithm for Increasing the Robustness of RED's AQM |
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* (Sally FLoyd, Ramakrishna Gummadi, and Scott Shenker) August 2001 |
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* |
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* Every 500 ms: |
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* if (avg > target and max_p <= 0.5) |
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* increase max_p : max_p += alpha; |
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* else if (avg < target and max_p >= 0.01) |
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* decrease max_p : max_p *= beta; |
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* |
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* target :[qth_min + 0.4*(qth_min - qth_max), |
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* qth_min + 0.6*(qth_min - qth_max)]. |
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* alpha : min(0.01, max_p / 4) |
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* beta : 0.9 |
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* max_P is a Q0.32 fixed point number (with 32 bits mantissa) |
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* max_P between 0.01 and 0.5 (1% - 50%) [ Its no longer a negative power of two ] |
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*/ |
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#define RED_ONE_PERCENT ((u32)DIV_ROUND_CLOSEST(1ULL<<32, 100)) |
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#define MAX_P_MIN (1 * RED_ONE_PERCENT) |
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#define MAX_P_MAX (50 * RED_ONE_PERCENT) |
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#define MAX_P_ALPHA(val) min(MAX_P_MIN, val / 4) |
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#define RED_STAB_SIZE 256 |
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#define RED_STAB_MASK (RED_STAB_SIZE - 1) |
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struct red_stats { |
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u32 prob_drop; /* Early probability drops */ |
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u32 prob_mark; /* Early probability marks */ |
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u32 forced_drop; /* Forced drops, qavg > max_thresh */ |
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u32 forced_mark; /* Forced marks, qavg > max_thresh */ |
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u32 pdrop; /* Drops due to queue limits */ |
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u32 other; /* Drops due to drop() calls */ |
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}; |
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struct red_parms { |
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/* Parameters */ |
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u32 qth_min; /* Min avg length threshold: Wlog scaled */ |
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u32 qth_max; /* Max avg length threshold: Wlog scaled */ |
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u32 Scell_max; |
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u32 max_P; /* probability, [0 .. 1.0] 32 scaled */ |
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/* reciprocal_value(max_P / qth_delta) */ |
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struct reciprocal_value max_P_reciprocal; |
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u32 qth_delta; /* max_th - min_th */ |
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u32 target_min; /* min_th + 0.4*(max_th - min_th) */ |
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u32 target_max; /* min_th + 0.6*(max_th - min_th) */ |
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u8 Scell_log; |
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u8 Wlog; /* log(W) */ |
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u8 Plog; /* random number bits */ |
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u8 Stab[RED_STAB_SIZE]; |
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}; |
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struct red_vars { |
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/* Variables */ |
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int qcount; /* Number of packets since last random |
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number generation */ |
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u32 qR; /* Cached random number */ |
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unsigned long qavg; /* Average queue length: Wlog scaled */ |
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ktime_t qidlestart; /* Start of current idle period */ |
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}; |
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static inline u32 red_maxp(u8 Plog) |
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{ |
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return Plog < 32 ? (~0U >> Plog) : ~0U; |
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} |
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static inline void red_set_vars(struct red_vars *v) |
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{ |
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/* Reset average queue length, the value is strictly bound |
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* to the parameters below, reseting hurts a bit but leaving |
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* it might result in an unreasonable qavg for a while. --TGR |
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*/ |
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v->qavg = 0; |
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v->qcount = -1; |
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} |
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static inline bool red_check_params(u32 qth_min, u32 qth_max, u8 Wlog, |
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u8 Scell_log, u8 *stab) |
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{ |
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if (fls(qth_min) + Wlog >= 32) |
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return false; |
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if (fls(qth_max) + Wlog >= 32) |
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return false; |
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if (Scell_log >= 32) |
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return false; |
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if (qth_max < qth_min) |
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return false; |
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if (stab) { |
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int i; |
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for (i = 0; i < RED_STAB_SIZE; i++) |
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if (stab[i] >= 32) |
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return false; |
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} |
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return true; |
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} |
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static inline int red_get_flags(unsigned char qopt_flags, |
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unsigned char historic_mask, |
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struct nlattr *flags_attr, |
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unsigned char supported_mask, |
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struct nla_bitfield32 *p_flags, |
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unsigned char *p_userbits, |
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struct netlink_ext_ack *extack) |
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{ |
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struct nla_bitfield32 flags; |
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if (qopt_flags && flags_attr) { |
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NL_SET_ERR_MSG_MOD(extack, "flags should be passed either through qopt, or through a dedicated attribute"); |
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return -EINVAL; |
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} |
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if (flags_attr) { |
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flags = nla_get_bitfield32(flags_attr); |
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} else { |
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flags.selector = historic_mask; |
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flags.value = qopt_flags & historic_mask; |
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} |
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*p_flags = flags; |
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*p_userbits = qopt_flags & ~historic_mask; |
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return 0; |
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} |
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static inline int red_validate_flags(unsigned char flags, |
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struct netlink_ext_ack *extack) |
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{ |
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if ((flags & TC_RED_NODROP) && !(flags & TC_RED_ECN)) { |
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NL_SET_ERR_MSG_MOD(extack, "nodrop mode is only meaningful with ECN"); |
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return -EINVAL; |
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} |
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return 0; |
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} |
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static inline void red_set_parms(struct red_parms *p, |
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u32 qth_min, u32 qth_max, u8 Wlog, u8 Plog, |
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u8 Scell_log, u8 *stab, u32 max_P) |
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{ |
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int delta = qth_max - qth_min; |
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u32 max_p_delta; |
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p->qth_min = qth_min << Wlog; |
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p->qth_max = qth_max << Wlog; |
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p->Wlog = Wlog; |
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p->Plog = Plog; |
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if (delta <= 0) |
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delta = 1; |
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p->qth_delta = delta; |
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if (!max_P) { |
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max_P = red_maxp(Plog); |
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max_P *= delta; /* max_P = (qth_max - qth_min)/2^Plog */ |
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} |
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p->max_P = max_P; |
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max_p_delta = max_P / delta; |
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max_p_delta = max(max_p_delta, 1U); |
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p->max_P_reciprocal = reciprocal_value(max_p_delta); |
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/* RED Adaptative target : |
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* [min_th + 0.4*(min_th - max_th), |
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* min_th + 0.6*(min_th - max_th)]. |
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*/ |
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delta /= 5; |
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p->target_min = qth_min + 2*delta; |
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p->target_max = qth_min + 3*delta; |
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p->Scell_log = Scell_log; |
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p->Scell_max = (255 << Scell_log); |
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if (stab) |
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memcpy(p->Stab, stab, sizeof(p->Stab)); |
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} |
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static inline int red_is_idling(const struct red_vars *v) |
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{ |
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return v->qidlestart != 0; |
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} |
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static inline void red_start_of_idle_period(struct red_vars *v) |
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{ |
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v->qidlestart = ktime_get(); |
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} |
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static inline void red_end_of_idle_period(struct red_vars *v) |
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{ |
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v->qidlestart = 0; |
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} |
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static inline void red_restart(struct red_vars *v) |
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{ |
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red_end_of_idle_period(v); |
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v->qavg = 0; |
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v->qcount = -1; |
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} |
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static inline unsigned long red_calc_qavg_from_idle_time(const struct red_parms *p, |
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const struct red_vars *v) |
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{ |
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s64 delta = ktime_us_delta(ktime_get(), v->qidlestart); |
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long us_idle = min_t(s64, delta, p->Scell_max); |
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int shift; |
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/* |
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* The problem: ideally, average length queue recalculation should |
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* be done over constant clock intervals. This is too expensive, so |
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* that the calculation is driven by outgoing packets. |
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* When the queue is idle we have to model this clock by hand. |
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* |
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* SF+VJ proposed to "generate": |
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* |
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* m = idletime / (average_pkt_size / bandwidth) |
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* |
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* dummy packets as a burst after idle time, i.e. |
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* |
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* v->qavg *= (1-W)^m |
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* |
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* This is an apparently overcomplicated solution (f.e. we have to |
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* precompute a table to make this calculation in reasonable time) |
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* I believe that a simpler model may be used here, |
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* but it is field for experiments. |
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*/ |
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shift = p->Stab[(us_idle >> p->Scell_log) & RED_STAB_MASK]; |
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if (shift) |
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return v->qavg >> shift; |
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else { |
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/* Approximate initial part of exponent with linear function: |
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* |
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* (1-W)^m ~= 1-mW + ... |
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* |
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* Seems, it is the best solution to |
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* problem of too coarse exponent tabulation. |
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*/ |
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us_idle = (v->qavg * (u64)us_idle) >> p->Scell_log; |
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if (us_idle < (v->qavg >> 1)) |
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return v->qavg - us_idle; |
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else |
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return v->qavg >> 1; |
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} |
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} |
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static inline unsigned long red_calc_qavg_no_idle_time(const struct red_parms *p, |
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const struct red_vars *v, |
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unsigned int backlog) |
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{ |
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/* |
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* NOTE: v->qavg is fixed point number with point at Wlog. |
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* The formula below is equvalent to floating point |
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* version: |
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* |
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* qavg = qavg*(1-W) + backlog*W; |
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* |
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* --ANK (980924) |
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*/ |
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return v->qavg + (backlog - (v->qavg >> p->Wlog)); |
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} |
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static inline unsigned long red_calc_qavg(const struct red_parms *p, |
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const struct red_vars *v, |
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unsigned int backlog) |
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{ |
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if (!red_is_idling(v)) |
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return red_calc_qavg_no_idle_time(p, v, backlog); |
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else |
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return red_calc_qavg_from_idle_time(p, v); |
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} |
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static inline u32 red_random(const struct red_parms *p) |
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{ |
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return reciprocal_divide(prandom_u32(), p->max_P_reciprocal); |
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} |
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static inline int red_mark_probability(const struct red_parms *p, |
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const struct red_vars *v, |
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unsigned long qavg) |
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{ |
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/* The formula used below causes questions. |
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OK. qR is random number in the interval |
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(0..1/max_P)*(qth_max-qth_min) |
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i.e. 0..(2^Plog). If we used floating point |
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arithmetics, it would be: (2^Plog)*rnd_num, |
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where rnd_num is less 1. |
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Taking into account, that qavg have fixed |
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point at Wlog, two lines |
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below have the following floating point equivalent: |
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max_P*(qavg - qth_min)/(qth_max-qth_min) < rnd/qcount |
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Any questions? --ANK (980924) |
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*/ |
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return !(((qavg - p->qth_min) >> p->Wlog) * v->qcount < v->qR); |
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} |
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enum { |
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RED_BELOW_MIN_THRESH, |
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RED_BETWEEN_TRESH, |
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RED_ABOVE_MAX_TRESH, |
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}; |
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static inline int red_cmp_thresh(const struct red_parms *p, unsigned long qavg) |
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{ |
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if (qavg < p->qth_min) |
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return RED_BELOW_MIN_THRESH; |
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else if (qavg >= p->qth_max) |
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return RED_ABOVE_MAX_TRESH; |
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else |
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return RED_BETWEEN_TRESH; |
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} |
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enum { |
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RED_DONT_MARK, |
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RED_PROB_MARK, |
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RED_HARD_MARK, |
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}; |
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static inline int red_action(const struct red_parms *p, |
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struct red_vars *v, |
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unsigned long qavg) |
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{ |
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switch (red_cmp_thresh(p, qavg)) { |
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case RED_BELOW_MIN_THRESH: |
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v->qcount = -1; |
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return RED_DONT_MARK; |
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case RED_BETWEEN_TRESH: |
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if (++v->qcount) { |
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if (red_mark_probability(p, v, qavg)) { |
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v->qcount = 0; |
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v->qR = red_random(p); |
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return RED_PROB_MARK; |
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} |
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} else |
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v->qR = red_random(p); |
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return RED_DONT_MARK; |
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case RED_ABOVE_MAX_TRESH: |
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v->qcount = -1; |
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return RED_HARD_MARK; |
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} |
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BUG(); |
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return RED_DONT_MARK; |
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} |
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static inline void red_adaptative_algo(struct red_parms *p, struct red_vars *v) |
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{ |
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unsigned long qavg; |
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u32 max_p_delta; |
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qavg = v->qavg; |
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if (red_is_idling(v)) |
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qavg = red_calc_qavg_from_idle_time(p, v); |
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/* v->qavg is fixed point number with point at Wlog */ |
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qavg >>= p->Wlog; |
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if (qavg > p->target_max && p->max_P <= MAX_P_MAX) |
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p->max_P += MAX_P_ALPHA(p->max_P); /* maxp = maxp + alpha */ |
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else if (qavg < p->target_min && p->max_P >= MAX_P_MIN) |
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p->max_P = (p->max_P/10)*9; /* maxp = maxp * Beta */ |
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max_p_delta = DIV_ROUND_CLOSEST(p->max_P, p->qth_delta); |
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max_p_delta = max(max_p_delta, 1U); |
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p->max_P_reciprocal = reciprocal_value(max_p_delta); |
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} |
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#endif
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