netdev - Re: [PATCH] TX_RING and packet mmap

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Date:	Tue, 21 Apr 2009 16:42:28 -0400 (EDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Johann Baudy <johann.baudy@...-log.net>
cc:	netdev@...r.kernel.org
Subject: Re: [PATCH] TX_RING and packet mmap

On Tue, 21 Apr 2009, Johann Baudy wrote:

> > 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.

Duh. So I cannot concurrently operate with multiple threads on the
structure.

The kernel synchronizes with itself via the socket?

> 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).

Ah ok.

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