*printf(9) and PRINTF_BUFR_SIZE

[dieterbsd at engineer.com]

>> While working on other problems with *printf(9), log(9), etc.
>> I stumbled upon:
>>
>> options PRINTF_BUFR_SIZE=128 # Prevent printf output being 
interspersed.
>>
>> Question 1: Am I correct in thinking that PRINTF_BUFR_SIZE is 
supposed
>> to prevent this:
>>
>>   ada2: 300.000MB/s transfuhub2: 3 ports with 3 removable, self 
powered
>>   ers (SATA 2.x, UDMA6, PIO 8192bytes)
>>   ada2: Command Queueing enabled
>>
>> Question 2: Why is vprintf() the only function that does this 
buffering?
>> As far as I can tell, the various functions that call kvprintf() 
directly
>> without going through vprintf() do not get buffered.  I'm thinking 
that
>> kvprintf() would be a better place for the buffering.  Or would this 
break
>> something?

> 
http://docs.freebsd.org/cgi/mid.cgi?AANLkTinPhcc8Z_BdvoEQUv-ZXlHAYOTQJwlUQDVO\
8iJ9

Thanks, Alex!  That was a useful thread, I now know more about the
problem and how to fix it.  I gather the answer to Q1 is yes.  Given
that the word "transfers" is broken, I still think this example is
most likely due to my changes that use unbuffered kvprintf() rather
than buffered vprintf().  So question 2 remains.

BTW, I see some threads where people think this is due to SMP.
It happens on uniprocessor machines too.