From e850f68b8f27a76c4377c34f2e216b8e7e10db3d Mon Sep 17 00:00:00 2001 From: Bob Copeland Date: Sat, 16 Jan 2010 14:36:52 -0500 Subject: mac80211: fix sign error in pid controller 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 Acked-by: Stefano Brivio Acked-by: Mattias Nissler Signed-off-by: John W. Linville --- net/mac80211/rc80211_pid_algo.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/net/mac80211/rc80211_pid_algo.c b/net/mac80211/rc80211_pid_algo.c index 699d3ed869c4..29bc4c516238 100644 --- a/net/mac80211/rc80211_pid_algo.c +++ b/net/mac80211/rc80211_pid_algo.c @@ -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; -- cgit v1.2.3-59-g8ed1b