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From: Russ Cox <rsc@swtch.com>
To: Fans of the OS Plan 9 from Bell Labs <9fans@cse.psu.edu>
Subject: Re: [9fans] Re: some Plan9 related ideas
Date: Mon, 17 Oct 2005 09:03:22 -0400	[thread overview]
Message-ID: <ee9e417a0510170603k1fc6728cjcf139dc12a1c041a@mail.gmail.com> (raw)
In-Reply-To: <20051017124559.GB29494@server4.lensbuddy.com>

> > > I was reading old archives, and I'm probably a bit dense; but what is
> > > the reason to use the same tag for the three messages?

> > The reason is you don't have to wait for the response to the first
> > before sending the second and third, avoiding two round trip times.

> Yes, but what I didn't understand is why you needed to use the same tag,
> I thought you could do this without chaning the protocol.

I redefined use of the same tag to mean "you have to finish the
previous message with this tag before processing this message",
so that if you send a Topen followed by a Tread and the open
blocks for whatever reason (disk i/o, say), the remote server
doesn't try to run the Tread and send back a "fid not in use"
error or some such.

> Could you explain with more detail how it would work from the (threaded)
> server POV? I was thinking that the server could use the fid to avoid
> threads stepping into each other, and still avoid having to change the
> protocol at all...

The threaded server would just have a list of requests associated with
each tag instead of a single request.  When it finishes one it can move
on to the next.

Under the current protocol you are not allowed to send a Tread request
using a fid that the server has not acknowleged via Rattach or Ropen.
So your approach still requires redefining the protocol.  Also I might have
multiple I/Os going on and not care what order they get handled.
Synchronization based on the fid changes current situations.  Basing it
on the tag uses what were previously illegal situations.

> And I'm still curious what kernel changes nemo was talking about.

Read his post where he talks about mount -U.

If you mean readf and writef, those weren't kernel changes.
They were the obvious library wrappers.

Russ


  reply	other threads:[~2005-10-17 13:03 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2005-08-29 23:23 [9fans] " Bhanu Nagendra Pisupati
2005-08-30 12:27 ` Sape Mullender
2005-08-30 15:21   ` Francisco Ballesteros
2005-08-30 15:25     ` Francisco Ballesteros
2005-08-30 17:07 ` [9fans] " Dave Eckhardt
2005-08-30 17:33   ` Francisco Ballesteros
2005-08-30 17:46     ` Russ Cox
2005-08-31  5:54       ` [9fans] tcs bug arisawa
2005-08-31  5:57         ` Rob Pike
2005-10-17  7:14       ` [9fans] Re: some Plan9 related ideas Uriel
2005-10-17 11:23         ` Russ Cox
2005-10-17 12:45           ` Uriel
2005-10-17 13:03             ` Russ Cox [this message]
2005-10-17 13:22               ` Uriel
2005-10-17 15:14                 ` Russ Cox

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