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. Cc: stefano.brivio@xxxxxxxxx Cc: mattias.nissler@xxxxxx Signed-off-by: Bob Copeland <me@xxxxxxxxxxxxxxx> --- Mattias / Stefano, please advise if I missed something. net/mac80211/rc80211_pid_algo.c | 2 +- 1 files changed, 1 insertions(+), 1 deletions(-) diff --git a/net/mac80211/rc80211_pid_algo.c b/net/mac80211/rc80211_pid_algo.c index 699d3ed..29bc4c5 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; -- 1.6.3.3 -- To unsubscribe from this list: send the line "unsubscribe linux-wireless" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
