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Changes between Version 15 and Version 16 of StuckBeacon

Author:
mentor (IP: 0.0.0.0)
Timestamp:
05/28/08 20:00:50 (11 years ago)
Comment:

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  • StuckBeacon

    v15 v16  
    33''This page, more than most, is a work-in-progress. If you have any detailed experience with the Stuck Beacon, please suffix it here.'' 
    44 
    5 The Stuck Beacon Problem (SBP) is an intermittant but severe problem for some users.  It has been around for a while, but has yet to be resolved.  Please help collect and report data on this bug by suffixing your experience to this page.  Since no one yet knows the basis for the problem, the meaures to report here will be refined over time.  Please read on for more hints. 
     5The Stuck Beacon Problem (SBP) is an intermittent but severe problem for some users.  It has been around for a while, but has yet to be resolved.  Please help collect and report data on this bug by suffixing your experience to this page.  Since no one yet knows the basis for the problem, the measures to report here will be refined over time.  Please read on for more hints. 
    66 
    7 Per Sam Leffler:   "stuck beacon" means the tx dma of the beacon frame failed to complete in a full beacon interval.  Diagnosing such a problem requires understanding why dma failed to complete.  This usually involves checking the dma descriptor for clues and/or looking at other h/w-related state.  If you have a "memory smash" then you will see it in the descriptor contents--but I doubt it.  In my experience this problem is usually caused by feeding bogus data to the dma engine that causes it to lockup but the problem in general is very complicated... 
     7Per Sam Leffler:   "stuck beacon" means the TX DMA of the beacon frame failed to complete in a full beacon interval.  Diagnosing such a problem requires understanding why DMA failed to complete.  This usually involves checking the DMA descriptor for clues and/or looking at other HW-related state.  If you have a "memory smash" then you will see it in the descriptor contents--but I doubt it.  In my experience this problem is usually caused by feeding bogus data to the DMA engine that causes it to lock-up but the problem in general is very complicated... 
    88 
    99To enable debug messages to help sort out the stuck beacon problem:  
    1212 80211debug +assoc +elemid 
    1313 
    14 The SBP is strictly an issue on AP's, stations don't have the Problem. The SBP is generally associated with a reduction in performance.  Data transfer rates drop.  Data may stop moving all together.  You may get a 'Stuck Beacon' message.  
     14The SBP is strictly an issue on APs, stations don't have the Problem. The SBP is generally associated with a reduction in performance.  Data transfer rates drop.  Data may stop moving all together.  You may get a 'Stuck Beacon' message.  
    1515 
    16 Anecdotal evidence suggests that the SBP occurs to varying degrees, and only the most severe are reported as 'Stuck Beacon'.  Some SBP's yield an simple error, but panics have been reported. 
     16Anecdotal evidence suggests that the SBP occurs to varying degrees, and only the most severe are reported as 'Stuck Beacon'.  Some SBPs yield an simple error, but panics have been reported. 
    1717 
    18 One of the measures that can indicate the problem is an ''acceleration'' in the card's hardware interrupt rate.  To watch the accumulation of interrupts on '''wifi0''', key in the folowing line from a console.  Substitute your interface name for '''wifi0''':  in the 'old' code, typically that is '''ath0''', and in the 'NG' code, the name of the base device, typically '''wifi0'''.  If the accumulation rate accelerates significantly, you may be heading towards a stuck beacon.  NB:  the count shown below will increase, and that is normal.  Accelerated rates are the issue. 
     18One of the measures that can indicate the problem is an ''acceleration'' in the card's hardware interrupt rate.  To watch the accumulation of interrupts on '''wifi0''', key in the following line from a console.  Substitute your interface name for '''wifi0''':  in the 'old' code, typically that is '''ath0''', and in the 'NG' code, the name of the base device, typically '''wifi0'''.  If the accumulation rate accelerates significantly, you may be heading towards a stuck beacon.  NB:  the count shown below will increase, and that is normal.  Accelerated rates are the issue. 
    1919 
    2020 watch -n 1 'cat /proc/interrupts | grep wifi0' 
    2121 
    22 Stuck Beacons can often be the result of a mis-installation or mis-configuration. It's been reported that changing settings stopped the stuck beacon (which settings you ask:  the reporter said "I don't remember which setting stopped that").   
     22Stuck Beacons can often be the result of a incorrect installation or misconfiguration. It's been reported that changing settings stopped the stuck beacon (which settings you ask:  the reporter said "I don't remember which setting stopped that").   
    2323 
    2424Another reporter using a D-link DWL-AG650 PCI card with drivers from CVS on 12/28/2005 encountered the SBP mostly when doing things that are network-intensive- RDesktop and VNC especially seem to trigger the problem. Watching a video recorded with MythTV induced the SBC and the video became choppy, though CPU idle was still over 90%. Downing the interface and rmmod ath_pci, sometimes helps, but not always, ie: got the SBP, downed the interface, removed the driver, re-inserted it, brought the interface back up, and that worked for another two hours. But after that, the SBP persisted through several down-remove-modprobe-up cycles.    
    2525 
    26 It appears that stuck beacon can be caused by wireless cards that have some sort of power saving feature, namely intel centrino (2200BG ) and equivalent cards. To fix this, turn the card out of power saving mode in the control panel, this may or may not fix the problem, but appeared to work for me. Uptime is around 10+days with latest madwifi drivers. More information specific to intel centrino laptops can be found here: http://support.intel.com/support/wireless/wlan/sb/cs-006205.htm 
     26It appears that stuck beacon can be caused by wireless cards that have some sort of power saving feature, namely Intel Centrino (2200BG) and equivalent cards. To fix this, turn the card out of power saving mode in the control panel, this may or may not fix the problem, but appeared to work for me. Uptime is around 10+ days with latest MadWiFi drivers. More information specific to Intel Centrino laptops can be found here: http://support.intel.com/support/wireless/wlan/sb/cs-006205.htm 
    2727 
    2828Here is a little perl script giving you the differences. Usage: store the code in a file, e.g. "madwifi.pl". Call it with  
    5353}}} 
    5454 
    55 I managed to cause stuckbeacon by changing channel while interface was up. To fix it, change channel on startup before interface is up and it appears to be fine. 
     55I managed to cause a SBP by changing channel while interface was up. To fix it, change channel on start-up before interface is up and it appears to be fine. 
    5656 
    5757Screenshot: 
    5858http://www.darktech.org.uk/stuckbeacon.jpg 
    59  
    60  
    6159 
    6260 
    7472 
    7573 
    76 Turning off BGSCAN with an iwpriv ath0 bgscan removed all stuck beacon messages from my server.  My configuration is setup with only one VAP in master mode running hostapd on a gentoo amd64 box.  I was getting about 200 stuck beacon messages per minute before turning off background scanning while idle.  I have not had a chance to test under load yet. 
     74Turning off background scanning with an 'iwpriv ath0 bgscan' removed all stuck beacon messages from my server.  My configuration is set-up with only one VAP in master mode running hostapd on a gentoo amd64 box.  I was getting about 200 stuck beacon messages per minute before turning off background scanning while idle.  I have not had a chance to test under load yet.