diff options
author | David S. Miller <davem@sunset.davemloft.net> | 2006-12-04 06:24:40 +0300 |
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committer | David S. Miller <davem@sunset.davemloft.net> | 2006-12-04 06:24:40 +0300 |
commit | 83ac58ba0a26228c0b16baa2c4b821de9c4ad5ca (patch) | |
tree | 6c8354a6314c39c5fa3f923e4095c16a5fed3d08 /net | |
parent | b4ad86bf52469b26148c677cb59d8bc81f129cc2 (diff) | |
parent | 2bbf29acd8f7adcf161de7e5d891b4095687a59f (diff) | |
download | linux-83ac58ba0a26228c0b16baa2c4b821de9c4ad5ca.tar.xz |
Merge master.kernel.org:/pub/scm/linux/kernel/git/acme/net-2.6
Diffstat (limited to 'net')
-rw-r--r-- | net/dccp/ccids/Kconfig | 33 | ||||
-rw-r--r-- | net/dccp/ccids/ccid3.c | 119 | ||||
-rw-r--r-- | net/dccp/ccids/ccid3.h | 2 | ||||
-rw-r--r-- | net/dccp/ccids/lib/tfrc_equation.c | 222 |
4 files changed, 237 insertions, 139 deletions
diff --git a/net/dccp/ccids/Kconfig b/net/dccp/ccids/Kconfig index dac89166eb18..80f469887691 100644 --- a/net/dccp/ccids/Kconfig +++ b/net/dccp/ccids/Kconfig @@ -89,4 +89,37 @@ config IP_DCCP_CCID3_DEBUG parameter to 0 or 1. If in doubt, say N. + +config IP_DCCP_CCID3_RTO + int "Use higher bound for nofeedback timer" + default 100 + depends on IP_DCCP_CCID3 && EXPERIMENTAL + ---help--- + Use higher lower bound for nofeedback timer expiration. + + The TFRC nofeedback timer normally expires after the maximum of 4 + RTTs and twice the current send interval (RFC 3448, 4.3). On LANs + with a small RTT this can mean a high processing load and reduced + performance, since then the nofeedback timer is triggered very + frequently. + + This option enables to set a higher lower bound for the nofeedback + value. Values in units of milliseconds can be set here. + + A value of 0 disables this feature by enforcing the value specified + in RFC 3448. The following values have been suggested as bounds for + experimental use: + * 16-20ms to match the typical multimedia inter-frame interval + * 100ms as a reasonable compromise [default] + * 1000ms corresponds to the lower TCP RTO bound (RFC 2988, 2.4) + + The default of 100ms is a compromise between a large value for + efficient DCCP implementations, and a small value to avoid disrupting + the network in times of congestion. + + The purpose of the nofeedback timer is to slow DCCP down when there + is serious network congestion: experimenting with larger values should + therefore not be performed on WANs. + + endmenu diff --git a/net/dccp/ccids/ccid3.c b/net/dccp/ccids/ccid3.c index 70ebe705eb75..cf8c07b2704f 100644 --- a/net/dccp/ccids/ccid3.c +++ b/net/dccp/ccids/ccid3.c @@ -121,12 +121,15 @@ static inline void ccid3_update_send_time(struct ccid3_hc_tx_sock *hctx) /* * Update X by * If (p > 0) - * x_calc = calcX(s, R, p); + * X_calc = calcX(s, R, p); * X = max(min(X_calc, 2 * X_recv), s / t_mbi); * Else * If (now - tld >= R) * X = max(min(2 * X, 2 * X_recv), s / R); * tld = now; + * + * If X has changed, we also update the scheduled send time t_now, + * the inter-packet interval t_ipi, and the delta value. */ static void ccid3_hc_tx_update_x(struct sock *sk, struct timeval *now) @@ -134,8 +137,7 @@ static void ccid3_hc_tx_update_x(struct sock *sk, struct timeval *now) struct ccid3_hc_tx_sock *hctx = ccid3_hc_tx_sk(sk); const __u32 old_x = hctx->ccid3hctx_x; - /* To avoid large error in calcX */ - if (hctx->ccid3hctx_p >= TFRC_SMALLEST_P) { + if (hctx->ccid3hctx_p > 0) { hctx->ccid3hctx_x_calc = tfrc_calc_x(hctx->ccid3hctx_s, hctx->ccid3hctx_rtt, hctx->ccid3hctx_p); @@ -223,16 +225,14 @@ static void ccid3_hc_tx_no_feedback_timer(unsigned long data) ccid3_tx_state_name(hctx->ccid3hctx_state)); /* Halve sending rate */ - /* If (X_calc > 2 * X_recv) + /* If (p == 0 || X_calc > 2 * X_recv) * X_recv = max(X_recv / 2, s / (2 * t_mbi)); * Else * X_recv = X_calc / 4; */ - BUG_ON(hctx->ccid3hctx_p >= TFRC_SMALLEST_P && - hctx->ccid3hctx_x_calc == 0); + BUG_ON(hctx->ccid3hctx_p && !hctx->ccid3hctx_x_calc); - /* check also if p is zero -> x_calc is infinity? */ - if (hctx->ccid3hctx_p < TFRC_SMALLEST_P || + if (hctx->ccid3hctx_p == 0 || hctx->ccid3hctx_x_calc > 2 * hctx->ccid3hctx_x_recv) hctx->ccid3hctx_x_recv = max_t(u32, hctx->ccid3hctx_x_recv / 2, hctx->ccid3hctx_s / (2 * TFRC_T_MBI)); @@ -245,9 +245,10 @@ static void ccid3_hc_tx_no_feedback_timer(unsigned long data) } /* * Schedule no feedback timer to expire in - * max(4 * R, 2 * s/X) = max(4 * R, 2 * t_ipi) + * max(t_RTO, 2 * s/X) = max(t_RTO, 2 * t_ipi) + * See comments in packet_recv() regarding the value of t_RTO. */ - t_nfb = max(4 * hctx->ccid3hctx_rtt, 2 * hctx->ccid3hctx_t_ipi); + t_nfb = max(hctx->ccid3hctx_t_rto, 2 * hctx->ccid3hctx_t_ipi); break; case TFRC_SSTATE_NO_SENT: DCCP_BUG("Illegal %s state NO_SENT, sk=%p", dccp_role(sk), sk); @@ -338,7 +339,7 @@ static int ccid3_hc_tx_send_packet(struct sock *sk, struct sk_buff *skb) * else * // send the packet in (t_nom - t_now) milliseconds. */ - if (delay >= hctx->ccid3hctx_delta) + if (delay - (long)hctx->ccid3hctx_delta >= 0) return delay / 1000L; break; case TFRC_SSTATE_TERM: @@ -412,10 +413,8 @@ static void ccid3_hc_tx_packet_recv(struct sock *sk, struct sk_buff *skb) struct dccp_tx_hist_entry *packet; struct timeval now; unsigned long t_nfb; - u32 t_elapsed; u32 pinv; - u32 x_recv; - u32 r_sample; + long r_sample, t_elapsed; BUG_ON(hctx == NULL); @@ -426,31 +425,44 @@ static void ccid3_hc_tx_packet_recv(struct sock *sk, struct sk_buff *skb) opt_recv = &hctx->ccid3hctx_options_received; - t_elapsed = dp->dccps_options_received.dccpor_elapsed_time * 10; - x_recv = opt_recv->ccid3or_receive_rate; - pinv = opt_recv->ccid3or_loss_event_rate; - switch (hctx->ccid3hctx_state) { case TFRC_SSTATE_NO_FBACK: case TFRC_SSTATE_FBACK: - /* Calculate new round trip sample by - * R_sample = (now - t_recvdata) - t_delay */ - /* get t_recvdata from history */ + /* get packet from history to look up t_recvdata */ packet = dccp_tx_hist_find_entry(&hctx->ccid3hctx_hist, DCCP_SKB_CB(skb)->dccpd_ack_seq); if (unlikely(packet == NULL)) { - DCCP_WARN("%s, sk=%p, seqno %llu(%s) does't exist " + DCCP_WARN("%s(%p), seqno %llu(%s) doesn't exist " "in history!\n", dccp_role(sk), sk, (unsigned long long)DCCP_SKB_CB(skb)->dccpd_ack_seq, dccp_packet_name(DCCP_SKB_CB(skb)->dccpd_type)); return; } - /* Update RTT */ + /* Update receive rate */ + hctx->ccid3hctx_x_recv = opt_recv->ccid3or_receive_rate; + + /* Update loss event rate */ + pinv = opt_recv->ccid3or_loss_event_rate; + if (pinv == ~0U || pinv == 0) + hctx->ccid3hctx_p = 0; + else + hctx->ccid3hctx_p = 1000000 / pinv; + dccp_timestamp(sk, &now); - r_sample = timeval_delta(&now, &packet->dccphtx_tstamp); - if (unlikely(r_sample <= t_elapsed)) - DCCP_WARN("r_sample=%uus,t_elapsed=%uus\n", + + /* + * Calculate new round trip sample as per [RFC 3448, 4.3] by + * R_sample = (now - t_recvdata) - t_elapsed + */ + r_sample = timeval_delta(&now, &packet->dccphtx_tstamp); + t_elapsed = dp->dccps_options_received.dccpor_elapsed_time * 10; + + if (unlikely(r_sample <= 0)) { + DCCP_WARN("WARNING: R_sample (%ld) <= 0!\n", r_sample); + r_sample = 0; + } else if (unlikely(r_sample <= t_elapsed)) + DCCP_WARN("WARNING: r_sample=%ldus <= t_elapsed=%ldus\n", r_sample, t_elapsed); else r_sample -= t_elapsed; @@ -473,31 +485,25 @@ static void ccid3_hc_tx_packet_recv(struct sock *sk, struct sk_buff *skb) hctx->ccid3hctx_t_ld = now; ccid3_update_send_time(hctx); - ccid3_hc_tx_set_state(sk, TFRC_SSTATE_FBACK); - } else { - hctx->ccid3hctx_rtt = (hctx->ccid3hctx_rtt * 9) / 10 + - r_sample / 10; - ccid3_hc_tx_update_x(sk, &now); - } - ccid3_pr_debug("%s, sk=%p, New RTT estimate=%uus, " - "r_sample=%us\n", dccp_role(sk), sk, - hctx->ccid3hctx_rtt, r_sample); + ccid3_pr_debug("%s(%p), s=%u, w_init=%u, " + "R_sample=%ldus, X=%u\n", dccp_role(sk), + sk, hctx->ccid3hctx_s, w_init, r_sample, + hctx->ccid3hctx_x); - /* Update receive rate */ - hctx->ccid3hctx_x_recv = x_recv;/* X_recv in bytes per sec */ + ccid3_hc_tx_set_state(sk, TFRC_SSTATE_FBACK); + } else { + hctx->ccid3hctx_rtt = (9 * hctx->ccid3hctx_rtt + + (u32)r_sample ) / 10; - /* Update loss event rate */ - if (pinv == ~0 || pinv == 0) - hctx->ccid3hctx_p = 0; - else { - hctx->ccid3hctx_p = 1000000 / pinv; + ccid3_hc_tx_update_x(sk, &now); - if (hctx->ccid3hctx_p < TFRC_SMALLEST_P) { - hctx->ccid3hctx_p = TFRC_SMALLEST_P; - ccid3_pr_debug("%s, sk=%p, Smallest p used!\n", - dccp_role(sk), sk); - } + ccid3_pr_debug("%s(%p), RTT=%uus (sample=%ldus), s=%u, " + "p=%u, X_calc=%u, X=%u\n", dccp_role(sk), + sk, hctx->ccid3hctx_rtt, r_sample, + hctx->ccid3hctx_s, hctx->ccid3hctx_p, + hctx->ccid3hctx_x_calc, + hctx->ccid3hctx_x); } /* unschedule no feedback timer */ @@ -512,16 +518,20 @@ static void ccid3_hc_tx_packet_recv(struct sock *sk, struct sk_buff *skb) */ sk->sk_write_space(sk); - /* Update timeout interval. We use the alternative variant of - * [RFC 3448, 3.1] which sets the upper bound of t_rto to one - * second, as it is suggested for TCP (see RFC 2988, 2.4). */ + /* + * Update timeout interval for the nofeedback timer. + * We use a configuration option to increase the lower bound. + * This can help avoid triggering the nofeedback timer too often + * ('spinning') on LANs with small RTTs. + */ hctx->ccid3hctx_t_rto = max_t(u32, 4 * hctx->ccid3hctx_rtt, - USEC_PER_SEC ); + CONFIG_IP_DCCP_CCID3_RTO * + (USEC_PER_SEC/1000) ); /* * Schedule no feedback timer to expire in - * max(4 * R, 2 * s/X) = max(4 * R, 2 * t_ipi) + * max(t_RTO, 2 * s/X) = max(t_RTO, 2 * t_ipi) */ - t_nfb = max(4 * hctx->ccid3hctx_rtt, 2 * hctx->ccid3hctx_t_ipi); + t_nfb = max(hctx->ccid3hctx_t_rto, 2 * hctx->ccid3hctx_t_ipi); ccid3_pr_debug("%s, sk=%p, Scheduled no feedback timer to " "expire in %lu jiffies (%luus)\n", @@ -535,7 +545,8 @@ static void ccid3_hc_tx_packet_recv(struct sock *sk, struct sk_buff *skb) hctx->ccid3hctx_idle = 1; break; case TFRC_SSTATE_NO_SENT: - DCCP_WARN("Illegal ACK received - no packet has been sent\n"); + if (dccp_sk(sk)->dccps_role == DCCP_ROLE_CLIENT) + DCCP_WARN("Illegal ACK received - no packet sent\n"); /* fall through */ case TFRC_SSTATE_TERM: /* ignore feedback when closing */ break; diff --git a/net/dccp/ccids/ccid3.h b/net/dccp/ccids/ccid3.h index 27cb20ae1da8..07596d704ef9 100644 --- a/net/dccp/ccids/ccid3.h +++ b/net/dccp/ccids/ccid3.h @@ -51,8 +51,6 @@ /* Parameter t_mbi from [RFC 3448, 4.3]: backoff interval in seconds */ #define TFRC_T_MBI 64 -#define TFRC_SMALLEST_P 40 - enum ccid3_options { TFRC_OPT_LOSS_EVENT_RATE = 192, TFRC_OPT_LOSS_INTERVALS = 193, diff --git a/net/dccp/ccids/lib/tfrc_equation.c b/net/dccp/ccids/lib/tfrc_equation.c index 2601012383fb..ddac2c511e2f 100644 --- a/net/dccp/ccids/lib/tfrc_equation.c +++ b/net/dccp/ccids/lib/tfrc_equation.c @@ -18,10 +18,79 @@ #include "tfrc.h" #define TFRC_CALC_X_ARRSIZE 500 +#define TFRC_CALC_X_SPLIT 50000 /* 0.05 * 1000000, details below */ +#define TFRC_SMALLEST_P (TFRC_CALC_X_SPLIT/TFRC_CALC_X_ARRSIZE) -#define TFRC_CALC_X_SPLIT 50000 -/* equivalent to 0.05 */ - +/* + TFRC TCP Reno Throughput Equation Lookup Table for f(p) + + The following two-column lookup table implements a part of the TCP throughput + equation from [RFC 3448, sec. 3.1]: + + s + X_calc = -------------------------------------------------------------- + R * sqrt(2*b*p/3) + (3 * t_RTO * sqrt(3*b*p/8) * (p + 32*p^3)) + + Where: + X is the transmit rate in bytes/second + s is the packet size in bytes + R is the round trip time in seconds + p is the loss event rate, between 0 and 1.0, of the number of loss + events as a fraction of the number of packets transmitted + t_RTO is the TCP retransmission timeout value in seconds + b is the number of packets acknowledged by a single TCP ACK + + We can assume that b = 1 and t_RTO is 4 * R. The equation now becomes: + + s + X_calc = ------------------------------------------------------- + R * sqrt(p*2/3) + (12 * R * sqrt(p*3/8) * (p + 32*p^3)) + + which we can break down into: + + s + X_calc = --------- + R * f(p) + + where f(p) is given for 0 < p <= 1 by: + + f(p) = sqrt(2*p/3) + 12 * sqrt(3*p/8) * (p + 32*p^3) + + Since this is kernel code, floating-point arithmetic is avoided in favour of + integer arithmetic. This means that nearly all fractional parameters are + scaled by 1000000: + * the parameters p and R + * the return result f(p) + The lookup table therefore actually tabulates the following function g(q): + + g(q) = 1000000 * f(q/1000000) + + Hence, when p <= 1, q must be less than or equal to 1000000. To achieve finer + granularity for the practically more relevant case of small values of p (up to + 5%), the second column is used; the first one ranges up to 100%. This split + corresponds to the value of q = TFRC_CALC_X_SPLIT. At the same time this also + determines the smallest resolution possible with this lookup table: + + TFRC_SMALLEST_P = TFRC_CALC_X_SPLIT / TFRC_CALC_X_ARRSIZE + + The entire table is generated by: + for(i=0; i < TFRC_CALC_X_ARRSIZE; i++) { + lookup[i][0] = g((i+1) * 1000000/TFRC_CALC_X_ARRSIZE); + lookup[i][1] = g((i+1) * TFRC_CALC_X_SPLIT/TFRC_CALC_X_ARRSIZE); + } + + With the given configuration, we have, with M = TFRC_CALC_X_ARRSIZE-1, + lookup[0][0] = g(1000000/(M+1)) = 1000000 * f(0.2%) + lookup[M][0] = g(1000000) = 1000000 * f(100%) + lookup[0][1] = g(TFRC_SMALLEST_P) = 1000000 * f(0.01%) + lookup[M][1] = g(TFRC_CALC_X_SPLIT) = 1000000 * f(5%) + + In summary, the two columns represent f(p) for the following ranges: + * The first column is for 0.002 <= p <= 1.0 + * The second column is for 0.0001 <= p <= 0.05 + Where the columns overlap, the second (finer-grained) is given preference, + i.e. the first column is used only for p >= 0.05. + */ static const u32 tfrc_calc_x_lookup[TFRC_CALC_X_ARRSIZE][2] = { { 37172, 8172 }, { 53499, 11567 }, @@ -525,85 +594,69 @@ static const u32 tfrc_calc_x_lookup[TFRC_CALC_X_ARRSIZE][2] = { { 243315981, 271305 } }; -/* Calculate the send rate as per section 3.1 of RFC3448 - -Returns send rate in bytes per second - -Integer maths and lookups are used as not allowed floating point in kernel - -The function for Xcalc as per section 3.1 of RFC3448 is: - -X = s - ------------------------------------------------------------- - R*sqrt(2*b*p/3) + (t_RTO * (3*sqrt(3*b*p/8) * p * (1+32*p^2))) - -where -X is the trasmit rate in bytes/second -s is the packet size in bytes -R is the round trip time in seconds -p is the loss event rate, between 0 and 1.0, of the number of loss events - as a fraction of the number of packets transmitted -t_RTO is the TCP retransmission timeout value in seconds -b is the number of packets acknowledged by a single TCP acknowledgement - -we can assume that b = 1 and t_RTO is 4 * R. With this the equation becomes: - -X = s - ----------------------------------------------------------------------- - R * sqrt(2 * p / 3) + (12 * R * (sqrt(3 * p / 8) * p * (1 + 32 * p^2))) - - -which we can break down into: - -X = s - -------- - R * f(p) - -where f(p) = sqrt(2 * p / 3) + (12 * sqrt(3 * p / 8) * p * (1 + 32 * p * p)) - -Function parameters: -s - bytes -R - RTT in usecs -p - loss rate (decimal fraction multiplied by 1,000,000) - -Returns Xcalc in bytes per second - -DON'T alter this code unless you run test cases against it as the code -has been manipulated to stop underflow/overlow. +/* return largest index i such that fval <= lookup[i][small] */ +static inline u32 tfrc_binsearch(u32 fval, u8 small) +{ + u32 try, low = 0, high = TFRC_CALC_X_ARRSIZE - 1; + + while (low < high) { + try = (low + high) / 2; + if (fval <= tfrc_calc_x_lookup[try][small]) + high = try; + else + low = try + 1; + } + return high; +} -*/ +/** + * tfrc_calc_x - Calculate the send rate as per section 3.1 of RFC3448 + * + * @s: packet size in bytes + * @R: RTT scaled by 1000000 (i.e., microseconds) + * @p: loss ratio estimate scaled by 1000000 + * Returns X_calc in bytes per second (not scaled). + * + * Note: DO NOT alter this code unless you run test cases against it, + * as the code has been optimized to stop underflow/overflow. + */ u32 tfrc_calc_x(u16 s, u32 R, u32 p) { int index; u32 f; u64 tmp1, tmp2; - if (p < TFRC_CALC_X_SPLIT) - index = (p / (TFRC_CALC_X_SPLIT / TFRC_CALC_X_ARRSIZE)) - 1; - else - index = (p / (1000000 / TFRC_CALC_X_ARRSIZE)) - 1; + /* check against invalid parameters and divide-by-zero */ + BUG_ON(p > 1000000); /* p must not exceed 100% */ + BUG_ON(p == 0); /* f(0) = 0, divide by zero */ + if (R == 0) { /* possible divide by zero */ + DCCP_CRIT("WARNING: RTT is 0, returning maximum X_calc."); + return ~0U; + } - if (index < 0) - /* p should be 0 unless there is a bug in my code */ - index = 0; + if (p <= TFRC_CALC_X_SPLIT) { /* 0.0000 < p <= 0.05 */ + if (p < TFRC_SMALLEST_P) { /* 0.0000 < p < 0.0001 */ + DCCP_WARN("Value of p (%d) below resolution. " + "Substituting %d\n", p, TFRC_SMALLEST_P); + index = 0; + } else /* 0.0001 <= p <= 0.05 */ + index = p/TFRC_SMALLEST_P - 1; - if (R == 0) { - DCCP_WARN("RTT==0, setting to 1\n"); - R = 1; /* RTT can't be zero or else divide by zero */ - } + f = tfrc_calc_x_lookup[index][1]; - BUG_ON(index >= TFRC_CALC_X_ARRSIZE); + } else { /* 0.05 < p <= 1.00 */ + index = p/(1000000/TFRC_CALC_X_ARRSIZE) - 1; - if (p >= TFRC_CALC_X_SPLIT) f = tfrc_calc_x_lookup[index][0]; - else - f = tfrc_calc_x_lookup[index][1]; + } + /* The following computes X = s/(R*f(p)) in bytes per second. Since f(p) + * and R are both scaled by 1000000, we need to multiply by 1000000^2. + * ==> DO NOT alter this unless you test against overflow on 32 bit */ tmp1 = ((u64)s * 100000000); tmp2 = ((u64)R * (u64)f); do_div(tmp2, 10000); do_div(tmp1, tmp2); - /* Don't alter above math unless you test due to overflow on 32 bit */ return (u32)tmp1; } @@ -611,33 +664,36 @@ u32 tfrc_calc_x(u16 s, u32 R, u32 p) EXPORT_SYMBOL_GPL(tfrc_calc_x); /* - * args: fvalue - function value to match - * returns: p closest to that value + * tfrc_calc_x_reverse_lookup - try to find p given f(p) * - * both fvalue and p are multiplied by 1,000,000 to use ints + * @fvalue: function value to match, scaled by 1000000 + * Returns closest match for p, also scaled by 1000000 */ u32 tfrc_calc_x_reverse_lookup(u32 fvalue) { - int ctr = 0; - int small; + int index; - if (fvalue < tfrc_calc_x_lookup[0][1]) + if (fvalue == 0) /* f(p) = 0 whenever p = 0 */ return 0; - if (fvalue <= tfrc_calc_x_lookup[TFRC_CALC_X_ARRSIZE - 1][1]) - small = 1; - else if (fvalue > tfrc_calc_x_lookup[TFRC_CALC_X_ARRSIZE - 1][0]) + /* Error cases. */ + if (fvalue < tfrc_calc_x_lookup[0][1]) { + DCCP_WARN("fvalue %d smaller than resolution\n", fvalue); + return tfrc_calc_x_lookup[0][1]; + } + if (fvalue > tfrc_calc_x_lookup[TFRC_CALC_X_ARRSIZE - 1][0]) { + DCCP_WARN("fvalue %d exceeds bounds!\n", fvalue); return 1000000; - else - small = 0; - - while (fvalue > tfrc_calc_x_lookup[ctr][small]) - ctr++; + } - if (small) - return TFRC_CALC_X_SPLIT * ctr / TFRC_CALC_X_ARRSIZE; - else - return 1000000 * ctr / TFRC_CALC_X_ARRSIZE; + if (fvalue <= tfrc_calc_x_lookup[TFRC_CALC_X_ARRSIZE - 1][1]) { + index = tfrc_binsearch(fvalue, 1); + return (index + 1) * TFRC_CALC_X_SPLIT / TFRC_CALC_X_ARRSIZE; + } + + /* else ... it must be in the coarse-grained column */ + index = tfrc_binsearch(fvalue, 0); + return (index + 1) * 1000000 / TFRC_CALC_X_ARRSIZE; } EXPORT_SYMBOL_GPL(tfrc_calc_x_reverse_lookup); |