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mac80211: fix sign error in pid controller

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While testing the pid rate controller in mac80211_hwsim, I noticed
that once the controller reached 54 Mbit rates, it would fail to
lower the rate when necessary.  The debug log shows:

1945 186786 pf_sample 50 3534 3577 50

My interpretation is that the fixed point scaling of the target
error value (pf) is incorrect: the error value of 50 compared to
a target of 14 case should result in a scaling value of
(14-50) = -36 * 256 or -9216, but instead it is (14 * 256)-50, or
3534.

Correct this by doing fixed point scaling after subtraction.

Signed-off-by: Bob Copeland <me@bobcopeland.com>
Acked-by: Stefano Brivio <stefano.brivio@polimi.it>
Acked-by: Mattias Nissler <mattias.nissler@gmx.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
This commit is contained in:
Bob Copeland 2010-01-16 14:36:52 -05:00 committed by John W. Linville
parent bb5d2db570
commit e850f68b8f
1 changed files with 1 additions and 1 deletions
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2
net/mac80211/rc80211_pid_algo.c
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@ -190,7 +190,7 @@ static void rate_control_pid_sample(struct rc_pid_info *pinfo,
rate_control_pid_normalize(pinfo, sband->n_bitrates);
/* Compute the proportional, integral and derivative errors. */
err_prop = (pinfo->target << RC_PID_ARITH_SHIFT) - pf;
err_prop = (pinfo->target - pf) << RC_PID_ARITH_SHIFT;
err_avg = spinfo->err_avg_sc >> pinfo->smoothing_shift;
spinfo->err_avg_sc = spinfo->err_avg_sc - err_avg + err_prop;