Date: Tue, 29 Jan 2008 21:20:03 GMT From: "=?ISO-8859-1?Q?Ermal_Lu=E7i?=" <ermal.luci@gmail.com> To: freebsd-pf@FreeBSD.org Subject: Re: kern/120057: [patch] Allow proper settings of ALTQ_HFSC. The check i wrong since even with the values forbidden from this check you get a concave curve. Message-ID: <200801292120.m0TLK3TC087305@freefall.freebsd.org>
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The following reply was made to PR kern/120057; it has been noted by GNATS.
From: "=?ISO-8859-1?Q?Ermal_Lu=E7i?=" <ermal.luci@gmail.com>
To: "Max Laier" <max@love2party.net>
Cc: bug-followup@freebsd.org, eri@freebsd.org
Subject: Re: kern/120057: [patch] Allow proper settings of ALTQ_HFSC. The check i wrong since even with the values forbidden from this check you get a concave curve.
Date: Tue, 29 Jan 2008 22:11:32 +0100
Following up, since i noticed that the mail was truncated.
Also not that the link you gave me, has the note:
<snip>
In order to decouple delay and bandwidth allocation, HFSC is designed
based on the service curve service model. In HFSC, only two-piece
linear service curves are used for simplicity. A two-piece linear
service curve is characterized by three parameters:
* m1, the slope of the first segment
* m2, the slope of the second segment
* d, the x-projection of the intersection point of the two segments
The following figure illustrates the two types of two-piece linear
service curves used in HFSC. For a convex curve (when m1 is less than
m2), m1 is always zero.
</snip>
But beware, that m1 here is in slope terms while m1 parameter of
service curves is not a slope! It is bytes per tick.
To check if a curve is concave, in the paper there is a proper formula
but needs some info that is not available at configuration time. But
as i said you cannot really configure a convex service curve.
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