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Use tc_calc_xmittime() where appropriate 

[IPROUTE]: Use tc_calc_xmittime() where appropriate

Replace expressions of the form "tc_core_usec2tick(1000000 * size/rate)"
by tc_calc_xmittime().

The CBQ case deserves an extra comment: when called with bnwd=rate,
tc_cbq_calc_maxidle() behaves identical to tc_calc_xmittime():

unsigned tc_cbq_calc_maxidle(...)
{
	double g = 1.0 - 1.0/(1<<ewma_log);
	double xmt = (double)avpkt/bndw;

	maxidle = xmt*(1-g);
	if (bndw != rate && maxburst) {
		...
	}
	return tc_core_usec2tick(maxidle*(1<<ewma_log)*1000000);
}

which comes down to:

maxidle	= xmt * (1 - g)
	= xmt * (1 - (1.0 - 1.0/(1 << ewma_log))
	= xmt * (1.0/(1 << ewma_log))

so:

maxidle * (1 << ewma_log) * 1000000
	= xmt * (1.0/(1 << ewma_log)) * (1 << ewma_log) * 1000000
	= xmt * 1000000
	= avpkt/bndw * 1000000

Which means tc_core_usec2tick(maxidle*(1<<ewma_log)*1000000) is identical
to tc_calc_xmittime(bndw, avpkt). Use it directly since its a lot easier
to understand its limits.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: Stephen Hemminger <shemminger@linux-foundation.org>
This commit is contained in:
Patrick McHardy 2007-03-04 20:14:56 +01:00 committed by Stephen Hemminger
parent 7b77c0caa6
commit 476daa7278
3 changed files with 3 additions and 3 deletions
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2
tc/q_cbq.c
View File

@ -147,7 +147,7 @@ static int cbq_parse_opt(struct qdisc_util *qu, int argc, char **argv, struct nl
if (ewma_log < 0)
ewma_log = TC_CBQ_DEF_EWMA;
lss.ewma_log = ewma_log;
lss.maxidle = tc_cbq_calc_maxidle(r.rate, r.rate, avpkt, lss.ewma_log, 0);
lss.maxidle = tc_calc_xmittime(r.rate, avpkt);
lss.change = TCF_CBQ_LSS_MAXIDLE|TCF_CBQ_LSS_EWMA|TCF_CBQ_LSS_AVPKT;
lss.avpkt = avpkt;

2
tc/tc_core.c
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@ -76,7 +76,7 @@ int tc_calc_rtable(unsigned bps, __u32 *rtab, int cell_log, unsigned mtu,
sz += overhead;
if (sz < mpu)
sz = mpu;
rtab[i] = tc_core_usec2tick(1000000*((double)sz/bps));
rtab[i] = tc_calc_xmittime(bps, sz);
}
return cell_log;
}

2
tc/tc_red.c
View File

@ -71,7 +71,7 @@ int tc_red_eval_ewma(unsigned qmin, unsigned burst, unsigned avpkt)
int tc_red_eval_idle_damping(int Wlog, unsigned avpkt, unsigned bps, __u8 *sbuf)
{
double xmit_time = tc_core_usec2tick(1000000*(double)avpkt/bps);
double xmit_time = tc_calc_xmittime(bps, avpkt);
double lW = -log(1.0 - 1.0/(1<<Wlog))/xmit_time;
double maxtime = 31/lW;
int clog;