On Tue, 10 Jul 2007 21:59:13 -0700, Cahill, Ben M wrote: > Postponing the division keeps the running average using more significant > bits, so each new sample has a meaningful, surviving impact to the > running average. Sorry, "high-precision" is the best term that I can > think of to describe more bits being used in the running average. The > "binary point" is between bits 3 and 4; think of bits 3:0 as > "remainder". Thanks, that makes sense. Please include something like this explanation in the description of the patch when you resend it. > There is a subtle difference between: > > 1) last_rssi * 15 / 16 > > 2) last_rssi - (last_rssi / 16) > > The first one would get stuck at -801 if there were a series of -51s > coming in. > -801 * 15 / 16 would get quantized to -750 each time, so the output > would be stuck at -801 (-50 dBm). > > The second one favors the high precision memory, and would progress from > -801 to -802, etc., as a series of -51s came in: > -801 - (-801/16) = -751 So it's basically just a different rounding - in the current code, it's like float division with the result rounded down, while your change makes it to round up (speaking about absolute value). Nothing about precision here :-) > I saw 2 instances of sta->last_rssi being used in ieee80211_ioctl.c, and > STA_FILE(last_rssi, last_rssi, D) in debugfs_sta.c, which I didn't > understand (still don't) and was afraid to touch, so I thought the > safest thing with least impact would be to add the 3 additional > variables, and do the division in one place for each of the 3 > rssi/signal/noise. > > If we do the division when passing to user space, how should STA_FILE be > handled, if necessary? Johannes was quicker than me (thanks) :-) > Thanks for your comments. I'll wait for your answer, and try again. Thanks and sorry for the delayed answer, Jiri -- Jiri Benc SUSE Labs - 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
