From mboxrd@z Thu Jan  1 00:00:00 1970
From: erik quanstrom <quanstro@quanstro.net>
Date: Wed, 28 Apr 2010 09:26:44 -0400
To: 9fans@9fans.net
Message-ID: <146005b4714b9e85c63d294ec9aa60dc@kw.quanstro.net>
In-Reply-To: <95FD9082-DC2A-44F9-BB4C-B221DB7A48FD@fastmail.fm>
References: <5fa9fbfe115a9cd5a81d0feefe413192@quintile.net>
	<95FD9082-DC2A-44F9-BB4C-B221DB7A48FD@fastmail.fm>
MIME-Version: 1.0
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: 8bit
Subject: Re: [9fans] A simple experiment
Topicbox-Message-UUID: 10a9af76-ead6-11e9-9d60-3106f5b1d025

> 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