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To: Fans of the OS Plan 9 from Bell Labs <9fans@9fans.net>
In-reply-to: Your message of "Mon, 20 Apr 2009 16:33:41 EDT."
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From: Bakul Shah <bakul+plan9@bitblocks.com>
Date: Tue, 21 Apr 2009 00:38:25 -0700
Message-Id: <20090421073825.48A935B24@mail.bitblocks.com>
Subject: Re: [9fans] Plan9 - the next 20 years
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On Mon, 20 Apr 2009 16:33:41 EDT erik quanstrom <quanstro@coraid.com>  wrote:
> let's take the path /sys/src/9/pc/sdata.c.  for http, getting
> this path takes one request (with the prefix http://$server)
> with 9p, this takes a number of walks, an open.  then you
> can start with the reads.  only the reads may be done in
> parallel.
>
> given network latency worth worring about, the total latency
> to read this file will be worse for 9p than for http.

Perhaps one can optimize for the common case by extending 9p
a bit: use special values for certain parameters to allow
sending consecutive Twalk, (Topen|Tcreate), (Tread|Twrite)
without waiting for intermeditate  R messages.  This makes
sense since the time to prepare /process a handful of
messages is much shorter than roundtrip latency.

A different performance problem arises when lots of data has
to be fetched.  You can pipeline data requests by having
multiple outstanding requests.  A further refinement would to
use something like RDMA -- in essence the receiver tells the
sender where exactly it wants the data delivered (thus
minimizing copying & processing).  You can very easily extend
the model to have data chunks delivered to different machines
in a cluster.  This is like separating a very high speed
"data plane" (with little or no processing) from a low speed
"control plane" (with lots of processing) in a modern
switch/router.