forked from Minki/linux
53ac9570c8
This patch simplifies the computation of t_ipi, avoiding expensive computations to enforce the minimum sending rate. Both RFC 3448 and rfc3448bis (revision #06), as well as RFC 4342 sec 5., require at various stages that at least one packet must be sent per t_mbi = 64 seconds. This requires frequent divisions of the type X_min = s/t_mbi, which are later converted back into an inter-packet-interval t_ipi_max = s/X_min = t_mbi. The patch removes the expensive indirection; in the unlikely case of having a sending rate less than one packet per 64 seconds, it also re-adjusts X. The following cases document conformance with RFC 3448 / rfc3448bis-06: 1) Time until receiving the first feedback packet: * if the sender has no initial RTT sample then X = s/1 Bps > s/t_mbi; * if the sender has an initial RTT sample or when the first feedback packet is received, X = W_init/R > s/t_mbi. 2) Slow-start (p == 0 and feedback packets come in): * RFC 3448 (current code) enforces a minimum of s/R > s/t_mbi; * rfc3448bis (future code) enforces an even higher minimum of W_init/R. 3) Congestion avoidance with no absence of feedback (p > 0): * when X_calc or X_recv/2 are too low, the minimum of X_min = s/t_mbi is enforced in update_x() when calling update_send_interval(); * update_send_interval() is, as before, only called when X changes (i.e. either when increasing or decreasing, not when in equilibrium). 4) Reduction of X without prior feedback or during slow-start (p==0): * both RFC 3448 and rfc3448bis here halve X directly; * the associated constraint X >= s/t_mbi is nforced here by send_interval(). 5) Reduction of X when p > 0: * X is modified indirectly via X_recv (RFC 3448) or X_recv_set (rfc3448bis); * in both cases, control goes back to section 4.3 (in both documents); * since p > 0, both documents use X = max(min(...), s/t_mbi), which is enforced in this patch by calling send_interval() from update_x(). I think that this analysis is exhaustive. Should I have forgotten a case, the worst-case consideration arises when X sinks below s/t_mbi, and is then increased back up to this minimum value. Even under this assumption, the behaviour is correct, since all lower limits of X in RFC 3448 / rfc3448bis are either equal to or greater than s/t_mbi. Note on the condition X >= s/t_mbi <==> t_ipi = s/X <= t_mbi: since X is scaled by 64, and all time units are in microseconds, the coded condition is: t_ipi = s * 64 * 10^6 usec / X <= 64 * 10^6 usec This simplifies to s / X <= 1 second <==> X * 1 second >= s > 0. (A zero `s' is not allowed by the CCID-3 code). Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk> |
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| 9p | ||
| 802 | ||
| 8021q | ||
| appletalk | ||
| atm | ||
| ax25 | ||
| bluetooth | ||
| bridge | ||
| can | ||
| core | ||
| dccp | ||
| decnet | ||
| econet | ||
| ethernet | ||
| ieee80211 | ||
| ipv4 | ||
| ipv6 | ||
| ipx | ||
| irda | ||
| iucv | ||
| key | ||
| lapb | ||
| llc | ||
| mac80211 | ||
| netfilter | ||
| netlabel | ||
| netlink | ||
| netrom | ||
| packet | ||
| rfkill | ||
| rose | ||
| rxrpc | ||
| sched | ||
| sctp | ||
| sunrpc | ||
| tipc | ||
| unix | ||
| wanrouter | ||
| wireless | ||
| x25 | ||
| xfrm | ||
| compat.c | ||
| Kconfig | ||
| Makefile | ||
| nonet.c | ||
| socket.c | ||
| sysctl_net.c | ||
| TUNABLE | ||