On Mon, May 17, 2010 at 8:00 PM, Nicolas Barati <nicolas.barati@gmail.com> wrote:
Hello all,
In my research on madwifi 's  back-off, eventually I got convinced that there is no way to see the current contention window 's value. So I turned to something else. I tried to disable backoff and then emulate a backoff scheme of my own  on driver level. I disabled backoff by  adding this:
qi.tqi_qflags |= HAL_TXQ_BACKOFF_DISABLE;   to ath_txq_setup().
Now I need a measure based on which my backoff emulation will increase/decrease  my_CW. I found in ath_tx_status these variables:
ast_longretry / ast_shortretry. I saw that these values are incremented only in ath_tx_processq() which is called from ath_tx_tasklet() or ath_tx_tasklet_q0(123)(). I read here : http://www.makelinux.net/ldd3/chp-7-sect-5.shtml about tasklet function and what I understood is that these functions are some kind of timer/scheduling functions.It sayes: "By scheduling a tasklet, you simply ask for it to be executed at a later time chosen by the kernel".
If It is so and these tasklet functions are called just some time in the future (regarding current kernel time)  and the long/shortretry variables are incremented only through ath_tx_processq when they are called, how accurate these variavles are in regard of the real state of retries. Are they to be trusted? Would you suggest that I consider these variables for my emulation??? And one more question, is disabling backoff done like how I said I did it above? And is there any way to see if it is indeed shut and not enabled again in some other part of the code or some time during the run time of the driver?

Thank you! 

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Hi,

 ath_tx_tasklet() is responsible to update information of each transmitted packet, please take a look on http://mesh.calit2.net/whzhao/madwifi_summary.pdf

  -  how accurate these variavles are in regard of the real state of retries. Are they to be trusted? Would you suggest that I consider these variables for my emulation???

Well, to test the accuracy of these variables, you can use a Network Analyzer  like Wireshrk, to see how many times a packet has been retransmitted,

I think that (ts->ts_longretry) is responsible ot store the number of long reties for each packet, but any way, you can test that and see by your self.

Hope this helps.


Regards,
--
Mohammad Jaser Abdelhadi
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Communications Engineering-Senior Student
Princess Sumaya University for Technology
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