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authorBob Copeland <me@bobcopeland.com>2010-01-16 14:36:52 -0500
committerJohn W. Linville <linville@tuxdriver.com>2010-01-18 15:07:02 -0500
commite850f68b8f27a76c4377c34f2e216b8e7e10db3d (patch)
tree0b2a6ffb15ede031c149d8c37a5ba359bb5695f8
parentbb5d2db5709e469f4a8c01eaaee9a275ed9772aa (diff)
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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 <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>
-rw-r--r--net/mac80211/rc80211_pid_algo.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/net/mac80211/rc80211_pid_algo.c b/net/mac80211/rc80211_pid_algo.c
index 699d3ed869c..29bc4c51623 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;