On Tue, Jul 20, 2010 at 06:04:59PM -0700, Bruno Randolf wrote: > On Tue July 20 2010 23:52:00 Bob Copeland wrote: > > > again, here my same concerns: printing the reasons for resets is > > > something which is useful on embedded boards and production setups which > > > can't have tracing enabled. which is why i want to object against this > > > change! > > > > What Johannes said wrt performance: during tracing, only the binary > > representations of the data are written to the trace ring buffer, so > > unlike the current debug code, we aren't doing printk formatting until > > the trace buffer is read. You can save the raw binary data from the > > trace and do formatting on another machine. > > that's true, but try to run a kernel with tracing compiled in and NOT runtime > enabled on a small embedded board (soekris net48xx for example) and you'll see > the difference. without tracing you can get 22Mbps, with tracing max 15Mbps > UDP thruput. that means you cannot run a kernel with tracing enabled on a > production system, which also means you cannot log the reasons for a reset > there any more. and most of the problems we what to trace (e.g. stuck queue) > happen only after days or weeks of operation in production environments... > > > Another advantage is better granularity: if you only care about watching > > tx on the cab queue, you can dynamically filter based on the tracepoint > > arguments, something like: > > > > # echo "qnum == 6" > /debug/tracing/events/ath5k/ath5k_tx/filter > > > > With the debug printks, you have to hack the driver or grep and hope > > the printk buffer didn't overflow and spill what you were looking for. > > no doubt, i can see the advantages... > > so let's go ahead with tracing, since we can always build less performant > tracing kernels when we want to track down problems. FWIW I intend on adding tracing as well to ath9k_hw on the hw-ops. Hence the hw-ops.h file, etc. Luis -- To unsubscribe from this list: send the line "unsubscribe linux-wireless" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
