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>

1 files changed, 1 insertions, 1 deletions

diff --git a/tc/tc_core.c b/tc/tc_core.c
index 10c375ef..90a097d3 100644
--- a/tc/tc_core.c
+++ b/tc/tc_core.c
@@ -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;
 }