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head/sys/netinet/cc/cc_cubic.h

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* SUCH DAMAGE. * SUCH DAMAGE.
* *
* $FreeBSD$ * $FreeBSD$
*/ */
#ifndef _NETINET_CC_CUBIC_H_ #ifndef _NETINET_CC_CUBIC_H_
#define _NETINET_CC_CUBIC_H_ #define _NETINET_CC_CUBIC_H_
#include <sys/limits.h>
/* Number of bits of precision for fixed point math calcs. */ /* Number of bits of precision for fixed point math calcs. */
#define CUBIC_SHIFT 8 #define CUBIC_SHIFT 8
#define CUBIC_SHIFT_4 32 #define CUBIC_SHIFT_4 32
/* 0.5 << CUBIC_SHIFT. */ /* 0.5 << CUBIC_SHIFT. */
#define RENO_BETA 128 #define RENO_BETA 128
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#define CUBIC_C_FACTOR 102 #define CUBIC_C_FACTOR 102
/* CUBIC fast convergence factor: (1+beta_cubic)/2. */ /* CUBIC fast convergence factor: (1+beta_cubic)/2. */
#define CUBIC_FC_FACTOR 217 #define CUBIC_FC_FACTOR 217
/* Don't trust s_rtt until this many rtt samples have been taken. */ /* Don't trust s_rtt until this many rtt samples have been taken. */
#define CUBIC_MIN_RTT_SAMPLES 8 #define CUBIC_MIN_RTT_SAMPLES 8
/*
* (2^21)^3 is long max. Dividing (2^63) by Cubic_C_factor
* and taking cube-root yields 448845 as the effective useful limit
*/
#define CUBED_ROOT_MAX_ULONG 448845
/* Userland only bits. */ /* Userland only bits. */
#ifndef _KERNEL #ifndef _KERNEL
extern int hz; extern int hz;
/* /*
* Implementation based on the formulae found in the CUBIC Internet Draft * Implementation based on the formulae found in the CUBIC Internet Draft
* "draft-ietf-tcpm-cubic-04". * "draft-ietf-tcpm-cubic-04".
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static __inline unsigned long static __inline unsigned long
cubic_cwnd(int ticks_since_cong, unsigned long wmax, uint32_t smss, int64_t K) cubic_cwnd(int ticks_since_cong, unsigned long wmax, uint32_t smss, int64_t K)
{ {
int64_t cwnd; int64_t cwnd;
/* K is in fixed point form with CUBIC_SHIFT worth of precision. */ /* K is in fixed point form with CUBIC_SHIFT worth of precision. */
/* t - K, with CUBIC_SHIFT worth of precision. */ /* t - K, with CUBIC_SHIFT worth of precision. */
cwnd = ((int64_t)(ticks_since_cong << CUBIC_SHIFT) - (K * hz)) / hz; cwnd = (((int64_t)ticks_since_cong << CUBIC_SHIFT) - (K * hz)) / hz;
if (cwnd > CUBED_ROOT_MAX_ULONG)
return INT_MAX;
if (cwnd < -CUBED_ROOT_MAX_ULONG)
return 0;
/* (t - K)^3, with CUBIC_SHIFT^3 worth of precision. */ /* (t - K)^3, with CUBIC_SHIFT^3 worth of precision. */
cwnd *= (cwnd * cwnd); cwnd *= (cwnd * cwnd);
/* /*
* C(t - K)^3 + wmax * C(t - K)^3 + wmax
* The down shift by CUBIC_SHIFT_4 is because cwnd has 4 lots of * The down shift by CUBIC_SHIFT_4 is because cwnd has 4 lots of
* CUBIC_SHIFT included in the value. 3 from the cubing of cwnd above, * CUBIC_SHIFT included in the value. 3 from the cubing of cwnd above,
* and an extra from multiplying through by CUBIC_C_FACTOR. * and an extra from multiplying through by CUBIC_C_FACTOR.
*/ */
cwnd = ((cwnd * CUBIC_C_FACTOR * smss) >> CUBIC_SHIFT_4) + wmax;
return ((unsigned long)cwnd); cwnd = ((cwnd * CUBIC_C_FACTOR) >> CUBIC_SHIFT_4) * smss + wmax;
/*
* for negative cwnd, limiting to zero as lower bound
*/
return (lmax(0,cwnd));
} }
/* /*
* Compute an approximation of the NewReno cwnd some number of ticks after a * Compute an approximation of the NewReno cwnd some number of ticks after a
* congestion event. RTT should be the average RTT estimate for the path * congestion event. RTT should be the average RTT estimate for the path
* measured over the previous congestion epoch and wmax is the value of cwnd at * measured over the previous congestion epoch and wmax is the value of cwnd at
* the last congestion event. The "TCP friendly" concept in the CUBIC I-D is * the last congestion event. The "TCP friendly" concept in the CUBIC I-D is
* rather tricky to understand and it turns out this function is not required. * rather tricky to understand and it turns out this function is not required.
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* the value of cwnd at the last congestion event. * the value of cwnd at the last congestion event.
*/ */
static __inline unsigned long static __inline unsigned long
tf_cwnd(int ticks_since_cong, int rtt_ticks, unsigned long wmax, tf_cwnd(int ticks_since_cong, int rtt_ticks, unsigned long wmax,
uint32_t smss) uint32_t smss)
{ {
/* Equation 4 of I-D. */ /* Equation 4 of I-D. */
return (((wmax * CUBIC_BETA) + (((THREE_X_PT3 * ticks_since_cong * return (((wmax * CUBIC_BETA) +
smss) << CUBIC_SHIFT) / TWO_SUB_PT3 / rtt_ticks)) >> CUBIC_SHIFT); (((THREE_X_PT3 * (unsigned long)ticks_since_cong *
(unsigned long)smss) << CUBIC_SHIFT) / (TWO_SUB_PT3 * rtt_ticks)))
>> CUBIC_SHIFT);
} }
#endif /* _NETINET_CC_CUBIC_H_ */ #endif /* _NETINET_CC_CUBIC_H_ */