[PD] latency, -frags, and -blocksize

[jfm3]

I am having a hard time conceptualizing what effect the -frags and 
-blocksize parameters have on Pd. I would like to get the best MIDI 
timing I can. I've fooled around with both parameters a bit, and it 
seems like -frags 2 -blocksize 256 is as small as I can get it without 
having even the test audio/midi patch buzzing. I seem to remember having 
these much smaller before. Does this sound about right? And what about 
-sleepgrain?

My laptop has a i8x0 sound card built in that I'm using. For MIDI I use 
the serial port and a MIDIator 124W. I have lowlatency patches applied 
to a 2.4.18 kernel, and am using ALSA 9b10. Thanks for any and all help.

(jfm3)