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--
-- RPC2's bandwidth and latency estimator
--
print "loading adaptive estimator"
-- These globals are set by RPC2
-- RPC2_RETRIES = 5
-- RPC2_TIMEOUT = time(15.0)
local RTT_SCALE = 8
local RTTVAR_SCALE = 4
local BW_SCALE = 16
local function estimate(host, bytes_sent, bytes_recv)
local BW_send, BW_recv, rtt_lat, rtt_send, rtt_recv, rto
BW_send, BW_recv = rtt_getbandwidth(host)
rtt_lat = host.RTT / RTT_SCALE
rtt_send = bytes_sent / BW_send
rtt_recv = bytes_recv / BW_recv
rto = rtt_lat + rtt_send + rtt_recv
return rto, rtt_lat, rtt_send, rtt_recv
end
local function update_bw(bw_lo, bw_hi, rtt, bytes)
local bw_cur, bw_est
local BW_SCALE = BW_SCALE
bw_cur = rtt / bytes
bw_est = 1 / bw_lo
bw_est = bw_est + (bw_cur - bw_est) / BW_SCALE
bw_lo = 1 / bw_est
bw_cur = bytes / rtt
bw_hi = bw_hi + (bw_cur - bw_hi) / BW_SCALE
return bw_lo, bw_hi
end
function rtt_init(host)
host.RTT = time(0)
host.RTTvar = time(0)
host.BW_send_lo = 100000
host.BW_send_hi = 100000
host.BW_recv_lo = 100000
host.BW_recv_hi = 100000
end
function rtt_update(host, elapsed, bytes_sent, bytes_recv)
local rto, rtt_lat, rtt_send, rtt_recv, err
-- Get current estimates
rto, rtt_lat, rtt_send, rtt_recv = estimate(host, bytes_sent, bytes_recv)
--[[
print("uRTT", host.name, elapsed, bytes_sent, bytes_recv, rto, rtt_lat,
host.BW_send_lo, host.BW_send_hi, host.BW_recv_lo, host.BW_recv_hi)
--]]
-- Calculate error and desired correction
if elapsed >= rto then
err = (elapsed - rto) / 3
rtt_send = rtt_send + err
rtt_recv = rtt_recv + err
else
err = elapsed / 3
rtt_send = err
rtt_recv = err
err = err - rtt_lat
end
-- Update estimates
host.RTT = host.RTT + err
err = err - host.RTTvar / RTTVAR_SCALE
host.RTTvar = host.RTTvar + err
host.BW_send_lo, host.BW_send_hi =
update_bw(host.BW_send_lo, host.BW_send_hi, rtt_send, bytes_sent)
host.BW_recv_lo, host.BW_recv_hi =
update_bw(host.BW_recv_lo, host.BW_recv_hi, rtt_recv, bytes_recv)
end
function rtt_getbandwidth(host)
local avg_send, avg_recv
avg_send = (host.BW_send_lo + host.BW_send_hi) / 2
avg_recv = (host.BW_recv_lo + host.BW_recv_hi) / 2
return avg_send, avg_recv
end
function rtt_getrto(host, bytes_sent, bytes_recv)
local rtt = (estimate(host, bytes_sent, bytes_recv))
-- print("est", host.name, rtt, bytes_sent, bytes_recv)
return rtt + host.RTTvar / 2
end
function rtt_retryinterval(host, attempt, bytes_sent, bytes_recv)
local rto, timeout, retry
if attempt > RPC2_RETRIES then return nil end
rto = (estimate(host, bytes_sent, bytes_recv))
if attempt == 0 then return rto end
timeout, retry = RPC2_TIMEOUT / 2, 0
for i = RPC2_RETRIES, 1, -1 do
if rto > timeout then retry = i break end
timeout = timeout / 2
end
if retry + attempt > RPC2_RETRIES then return nil end
for i = 1, attempt do timeout = timeout * 2 end
return timeout
end
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