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Driver API tracing
Enabling
Since 2.6.32 mac80211 includes a tracing framework, and since 3.2 it is always enabled if possible (if EVENT_TRACING is enabled in the kernel.)
To be able to use it on kernels before 3.2, enable
CONFIG_MAC80211_DRIVER_API_TRACER
(requires tracing and
CONFIG_MAC80211_DEBUG_MENU
).
Using trace-cmd
The easiest way to give a trace to other people is to use trace-cmd, see also https://lwn.net/Articles/410200/. To record a trace with trace-cmd, use
trace-cmd record -e mac80211
This will record until you hit Ctrl-C to abort. The result is stored in a file “trace.dat” which you can send around for analysis. You should compress it before sending it to other people since it is relatively large but compresses well.
To analyse a file, use
trace-cmd report -i trace.dat | less
cfg80211 and wpasupplicant
Both cfg80211 and wpasupplicant have tracing support. Use '-e cfg80211' with trace-cmd to enable all cfg80211 tracing points. For wpasupplicant enable CONFIG_DEBUG_LINUX_TRACING build config and use -T switch to get log messages sent to the tracing framework.
Driver tracing
In addition to mac80211, some drivers include tracing as well.
iwlwifi
For iwlwifi, set the
IWLWIFI_DEVICE_TRACING
Kconfig option. You can then get new trace subsystems:
; iwlwifi : the commands exchanged between driver and device ; iwlwifi_io : the device IO accesses and interrupt information ; iwlwifi_msg : all debug messages from the driver ; iwlwifi_ucode : uCode events (not sure they're useful today) ; iwlwifi_data : data for TX/RX frames
Recommended:
trace-cmd record -e mac80211 -e mac80211_msg -e iwlwifi -e iwlwifi_msg -e iwlwifi_data
