Slow roaming in mac80211 (2.6.30).

[Lam Yoke Khei]

Hi Lars,

    Would you mind to share your idea or patches on 2.6.26 kernel to improve 
roaming? As I am investigating the solution for short handoff/reassociation 
time (~50ms) via linux wireless stack. Thanks in advance.

Best regards,
Lam

----- Original Message ----- 
From: "Lars Ericsson" <Lars_Ericsson at telia.com>
To: "'Johannes Berg'" <johannes at sipsolutions.net>
Cc: <linux-wireless at vger.kernel.org>; <hostap at shmoo.com>
Sent: Wednesday, July 22, 2009 5:21 AM
Subject: Slow roaming in mac80211 (2.6.30).


>
> Johannes,
>
> I'm currently using the 2.6.26 kernel and have started evaluating the
> 2.6.30.
>
> For .26 I have made a few patches to fix minor issues related to
> roaming.
>
> The trace below shows a typical roaming:
> 87.632965 AP 1 drops STA
> 87.733979 wpa_supplicant trigs a scan
> 88.629931 mac80211 probes for the old AP
> 90.670305 SCAN result to wpa_supplicant
> 90.702325 wpa_supplicant ready with new AP
> 92.158037 mac80211 executes the wpa_supplicant decisions
> 92.164776 we are on line again
>
> Total roaming time is 4,5 seconds, where mac80211 had added 2*2
> seconds delay.
>
> A first analysis gives that the two delays are the ieee80211_sta_work()
> timeout.  There are many events trigging ieee80211_sta_work(), but
> since only the timer sets IEEE80211_STA_REQ_RUN, nothing will happen.
>
> Questions;
> - Why does mac80211 tells the wpa_supplicant that the AP
> is gone (87.632965), and then blocks/delays the actions taken by the
> wpa_supplicant?
> - Why are some wpa_supplicant actions (90.702325)
> not event driven?
>
> It looks to me as if we have to decision makers here. For me the
> wpa_supplicant is the one that make the decision. Once the mac80211
> gives up and feedback that the AP is gone, it should just sit
> and wait for next decision from the wpa_supplicant.
>
> I had a few patches for this for .26, but since the code is changed
> they do not apply. Before I create new patches I would like to get
> your opinion on this.
>
> Regards
> /Lars
>
> -----
> [   87.632965] wlan0: deauthenticated (Reason: 1)
> [   87.733979] [B] LaE: SCANRQUEST: SSID=AGV
> [   88.629931] wlan0: direct probe to AP 00:40:96:a0:e7:e7 try 1
> [   88.829932] wlan0: direct probe to AP 00:40:96:a0:e7:e7 try 2
> [   89.029944] wlan0: direct probe to AP 00:40:96:a0:e7:e7 try 3
> [   89.230016] wlan0: direct probe to AP 00:40:96:a0:e7:e7 timed out
> [   90.670305] [B] LaE: SCANRESULT: BSSID=00:40:96:a0:e7:e7, SSID=
> , ch= 1, , q=  0, l=  0(-30dBm), n=  0
> [   90.670384] [B] LaE: SCANRESULT: BSSID=00:08:21:31:53:87, SSID=
> , ch=11, , q=  0, l=  0(-62dBm), n=  0
> [   90.670455] [B] LaE: SCANRESULT: BSSID=00:08:21:31:53:87, SSID=AGV
> , ch=11, , q=  0, l=  0(-60dBm), n=  0
> [   90.670705] ieee80211_ioctl_siwauth: enter
> [   90.670777] ieee80211_ioctl_siwencodeext: enter
> [   90.670807] ieee80211_set_encryption: enter
> [   90.671128] ieee80211_ioctl_siwencodeext: enter
> [   90.671165] ieee80211_set_encryption: enter
> [   90.671219] ieee80211_ioctl_siwencodeext: enter
> [   90.671247] ieee80211_set_encryption: enter
> [   90.671297] ieee80211_ioctl_siwencodeext: enter
> [   90.671325] ieee80211_set_encryption: enter
> [   90.671375] ieee80211_ioctl_siwencodeext: enter
> [   90.671404] ieee80211_set_encryption: enter
> [   90.671623] ieee80211_ioctl_siwencodeext: enter
> [   90.671659] ieee80211_set_encryption: enter
> [   90.672062] ieee80211_ioctl_siwauth: enter
> [   90.672295] ieee80211_ioctl_siwgenie: enter
> [   90.672332] ieee80211_sta_req_auth: queue auth
> [   90.672380] ieee80211_ioctl_siwauth: enter
> [   90.672420] ieee80211_ioctl_siwauth: enter
> [   90.672458] ieee80211_ioctl_siwauth: enter
> [   90.672495] ieee80211_ioctl_siwauth: enter
> [   90.672532] ieee80211_ioctl_siwauth: enter
> [   90.672569] ieee80211_ioctl_siwauth: enter
> [   90.672612] ieee80211_ioctl_siwfreq: enter freq=246200000
> [   90.702175] ieee80211_ioctl_siwessid: enter ssid=AGV
> [   90.702217] ieee80211_sta_req_auth: queue auth
> [   90.702325] ieee80211_ioctl_siwap: enter AP=00:08:21:31:53:87
> [   90.702372] ieee80211_sta_req_auth: queue auth
> [   92.158037] wlan0: authenticate with AP 00:08:21:31:53:87
> [   92.159965] wlan0: authenticated
> [   92.160002] wlan0: associate with AP 00:08:21:31:53:87
> [   92.164733] wlan0: RX ReassocResp from 00:08:21:31:53:87 (capab=0x431
> status=0 aid=140)
> [   92.164776] wlan0: associated
> [   92.166984] ieee80211_ioctl_giwap: enter
>
> -----
>
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