Hi,
while watching the rc_stats of minstrel, I noticed
that minstrel does not choose the rate with best throughput.
For example, I often see something like this:
rate throughput ewma prob this prob this succ/attempt success attempts
1 0.8 89.1 100.0 0( 0) 1490 2257
2 1.8 95.3 100.0 0( 0) 13 15
5.5 4.8 95.5 100.0 0( 0) 17 22
P 11 9.4 98.5 100.0 0( 0) 1532 2195
6 5.4 95.6 100.0 0( 0) 28 88
9 8.1 96.2 100.0 0( 0) 143 431
12 8.7 78.8 100.0 0( 0) 209 814
18 12.3 75.8 100.0 0( 0) 302 2416
24 18.3 86.2 100.0 0( 0) 5765 9196
36 2.6 85.2 100.0 0( 0) 736813 886517
T 48 14.7 97.4 100.0 2( 2) 3433862 4411674
t 54 8.5 73.3 100.0 0( 0) 1488241 2180261
Why did minstrel chose the 48M rate, and not 24M for the best throughput rate?
Also "this prob" seems fishy to me, its always 100...
Another thing: I noticed that the througput field in minstrel_rate is never used?
Should I send a patch, removing it? Or does anyone remember why it was there
in the first place?
Best regards,
Arnd
P.S. runnning 2.6.31-rc6 with ath5k...
Arnd Hannemann wrote:
> Hi,
>
> while watching the rc_stats of minstrel, I noticed
> that minstrel does not choose the rate with best throughput.
> For example, I often see something like this:
>
> rate throughput ewma prob this prob this succ/attempt success attempts
> 1 0.8 89.1 100.0 0( 0) 1490 2257
> 2 1.8 95.3 100.0 0( 0) 13 15
> 5.5 4.8 95.5 100.0 0( 0) 17 22
> P 11 9.4 98.5 100.0 0( 0) 1532 2195
> 6 5.4 95.6 100.0 0( 0) 28 88
> 9 8.1 96.2 100.0 0( 0) 143 431
> 12 8.7 78.8 100.0 0( 0) 209 814
> 18 12.3 75.8 100.0 0( 0) 302 2416
> 24 18.3 86.2 100.0 0( 0) 5765 9196
> 36 2.6 85.2 100.0 0( 0) 736813 886517
> T 48 14.7 97.4 100.0 2( 2) 3433862 4411674
> t 54 8.5 73.3 100.0 0( 0) 1488241 2180261
>
>
> Why did minstrel chose the 48M rate, and not 24M for the best throughput rate?
The table looks weird. Maybe there's a race between the update of the
table and the display through debugfs. Either way, 48M is definitely the
best throughput rate based on the ewma prob, but the calculated
throughput value looks a bit off.
> Also "this prob" seems fishy to me, its always 100...
"this prob" refers to the current interval, not the value after EWMA, so
it's always calculated from this succ/attempt and 100.0 makes sense here.
> Another thing: I noticed that the througput field in minstrel_rate is never used?
> Should I send a patch, removing it? Or does anyone remember why it was there
> in the first place?
I think you can remove it. I think initially I planned on calculating
both the EWMA throughput and the one from the measurement interval, but
didn't do that, because it's not displayed anywhere and would serve no
other purpose.
- Felix