[9fans] 9P - Meaning of iounit

[9fans] 9P - Meaning of iounit

[Chris McGee]

Hello All,

I am learning the 9p protocol and implementing a 9P server. After reading the 9p manual page, the types of messages and much of the overview is clear. There are a number of items that are less clear.

For example, it took some time to figure out how to provide a directory structure on a Tread.

Lately, I’m looking at the “iounit.” Initially, I had thought of it as a way to give the size of a file on Topen. After some testing I realized that the network subsystem in plan9 is expecting the iounit to be large enough to write commands into a /net/tcp ctl file. With a small iounit, the network subsystem truncates the commands, such as “connect xyz|1234” to match the size of the iounit.

So, what is this mysterious iounit? Is there another man page or plan9 document that describes it in more detail?

Thanks,
Chris

Re: [9fans] 9P - Meaning of iounit

[Richard Miller]

term% lookman iounit
man 2 fcall # fcall(2)
man 2 iounit # iounit(2)
man 3 proc # proc(3)
man 5 0intro # 0intro(5)
man 5 open # open(5)
man 5 read # read(5)

Re: [9fans] 9P - Meaning of iounit

[James A. Robinson]

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On Mon, Oct 3, 2016 at 6:54 AM Chris McGee <newton688@gmail.com> wrote:

> Lately, I’m looking at the “iounit.” Initially, I had thought of it as a
> way to give the size of a file on Topen. After some testing I realized that
> the network subsystem in plan9 is expecting the iounit to be large enough
> to write commands into a /net/tcp ctl file. With a small iounit, the
> network subsystem truncates the commands, such as “connect xyz|1234” to
> match the size of the iounit.
>
> So, what is this mysterious iounit? Is there another man page or plan9
> document that describes it in more detail?
>

Given that there are comments like this:

/* ample room for Twrite/Rread header (iounit) */

paired with an old message from Mr. Quanstrom below, I suspect the
value is "as large as your network / disk can manage, but at least as large
as the protocol overhead".  But that's just a WAG.

---------- Forwarded message ---------
From: erik quanstrom <quanstro@quanstro.net>
Date: Sat, Nov 16, 2013 at 6:45 PM
Subject: [9fans] simple gofast trick
To: <9fans@9fans.net>


this is a one-liner.  here's a little demo:

        chula; sed 's:8192:64*1024:g' </sys/src/cmd/cat.c > fatcat.c && tmk
fatcat.c
        6c -FVTw fatcat.c
        6l -o 6.fatcat fatcat.6
        chula; cat /bin/gs>/dev/null;for(i in cat 6.fatcat)time $i /bin/gs
> /dev/null
        0.00u 0.01s 0.41r        cat /bin/gs
        0.00u 0.00s 0.23r        6.fatcat /bin/gs

the trick is only to increase IOUNIT to 48k in both file server and cpu
server.

this works since the mtu of the network is 1500 bytes and the Rread messages
are up to 48k + 9p overhead, the network layer has multiple outstanding
messages and overlapping acks at the network layer much of the time, even
though the mount driver continues keeping a single outstanding message
per system call.

- erik

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Re: [9fans] 9P - Meaning of iounit

[Jules Merit]

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I agree with Eric*com. Rice rice baby, popo. Don't Tread on my 9p server.

On Mon, Oct 3, 2016 at 8:08 AM, James A. Robinson <jimr@highwire.org> wrote:

> On Mon, Oct 3, 2016 at 6:54 AM Chris McGee <newton688@gmail.com> wrote:
>
>> Lately, I’m looking at the “iounit.” Initially, I had thought of it as a
>> way to give the size of a file on Topen. After some testing I realized that
>> the network subsystem in plan9 is expecting the iounit to be large enough
>> to write commands into a /net/tcp ctl file. With a small iounit, the
>> network subsystem truncates the commands, such as “connect xyz|1234” to
>> match the size of the iounit.
>>
>> So, what is this mysterious iounit? Is there another man page or plan9
>> document that describes it in more detail?
>>
>
> Given that there are comments like this:
>
> /* ample room for Twrite/Rread header (iounit) */
>
> paired with an old message from Mr. Quanstrom below, I suspect the
> value is "as large as your network / disk can manage, but at least as
> large as the protocol overhead".  But that's just a WAG.
>
> ---------- Forwarded message ---------
> From: erik quanstrom <quanstro@quanstro.net>
> Date: Sat, Nov 16, 2013 at 6:45 PM
> Subject: [9fans] simple gofast trick
> To: <9fans@9fans.net>
>
>
> this is a one-liner.  here's a little demo:
>
>         chula; sed 's:8192:64*1024:g' </sys/src/cmd/cat.c > fatcat.c &&
> tmk fatcat.c
>         6c -FVTw fatcat.c
>         6l -o 6.fatcat fatcat.6
>         chula; cat /bin/gs>/dev/null;for(i in cat 6.fatcat)time $i /bin/gs
> > /dev/null
>         0.00u 0.01s 0.41r        cat /bin/gs
>         0.00u 0.00s 0.23r        6.fatcat /bin/gs
>
> the trick is only to increase IOUNIT to 48k in both file server and cpu
> server.
>
> this works since the mtu of the network is 1500 bytes and the Rread
> messages
> are up to 48k + 9p overhead, the network layer has multiple outstanding
> messages and overlapping acks at the network layer much of the time, even
> though the mount driver continues keeping a single outstanding message
> per system call.
>
> - erik
>
>

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Re: [9fans] 9P - Meaning of iounit

[Chris McGee]

Thanks Richard, James,

Chris

> On Oct 3, 2016, at 11:05 AM, Richard Miller <9fans@hamnavoe.com> wrote:
>
> term% lookman iounit
> man 2 fcall # fcall(2)
> man 2 iounit # iounit(2)
> man 3 proc # proc(3)
> man 5 0intro # 0intro(5)
> man 5 open # open(5)
> man 5 read # read(5)
>
>

[9fans] 9p - meaning of iounit

[Chris McGee]

Hello All,

I am learning the 9p protocol and implementing a 9P server. After reading the 9p manual page, the types of messages and much of the overview is clear. There are a number of items that are less clear.

For example, it took some time to figure out how to provide a directory structure on a Tread.

Lately, I?m looking at the ?iounit.? Initially, I had thought of it as a way to give the size of a file on Topen. After some testing I realized that the network subsystem in plan9 is expecting the iounit to be large enough to write commands into a /net/tcp ctl file. With a small iounit, the network subsystem truncates the commands, such as ?connect xyz|1234? to match the size of the iounit.

So, what is this mysterious iounit? Is there another man page or plan9 document that describes it in more detail?

Thanks,
Chris