netdev - Re: [PATCH] TX_RING and packet mmap

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Message-ID: <7e0dd21a0904211313p73143cc8t51b5c537c5edfb05@mail.gmail.com>
Date:	Tue, 21 Apr 2009 22:13:35 +0200
From:	Johann Baudy <johann.baudy@...-log.net>
To:	Christoph Lameter <cl@...ux.com>
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH] TX_RING and packet mmap

Hi Christoph,

> Could you clean then states up a bit to reflect what they actually mean?
>
> TP_STATUS_AVAILABLE             => Frame is available
> TP_STATUS_SEND_REQUEST          => Frame waits for sending
> TP_STATUS_SENDING               => Frame is being sent.

Ok

> Also can you ensure that send() continues to send if I concurrently set
> the status to TP_STATUS_SEND_REQUEST from another thread? How it is
> serialized anyways? Status is an atomic value? Or do you rely on status
> only being modified while send() is running?

TP_STATUS_KERNEL => TP_STATUS_SEND_REQUEST: only performed by user.
TP_STATUS_SEND_REQUEST => TP_STATUS_SENDING  only performed by kernel
TP_STATUS_SENDING => TP_STATUS_KERNEL  only performed by kernel.

Only one thread is allowed to change status values from user space.
This way, you can take advantage of smp. One thread is filling the
buffer changing status  from TP_STATUS_KERNEL to
TP_STATUS_SEND_REQUEST , another is calling send() in loop
(MSG_DONTBLOCK option can be used).

You can also perform filling and send() sequentially

An example can be found at:
http://wiki.gnu-log.net/index.php5?title=Linux_packet_mmap
It can customize almost all parameters, use multi_thread, use DGRAM ...

Thanks,
Johann
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