> Could round-trip times be adding up? Does 9p do one file at once > strictly?
i think you mean, does 9p have 1 outstanding message. it does not. 9p supports having as many outstanding messages as one wishes. if you do a pread(2), the kernel will only maintain a single outstanding message for you. fcp is a quick hack around this. by keeping n threads each doing a read, you can keep n messages outstanding. there is nothing (save complexity) preventing the kernel from keeping multiple outstanding 9p messages. this is the technique aoe uses to overcome drive latency, which — even for enterprise slc ssds — can be considerable in the worst case (~500ms). - erik
