Re: [RFC][PATCH] TTY flip buffer SMP changes

[Alan Cox <alan@lxorguk.ukuu.org.uk>]

On Gwe, 2004-10-08 at 14:35, Paul Fulghum wrote:
> It does seem to carry serious overhead (in relation
> to ring buffers) for devices with small FIFOs.

Thats one reason I wanted sk_buff like rather than sk_buff. I want
to be able to recycle buffers back to drivers when the driver thinks
its the right thing to do.

Then you get something like

next_buffer()
{
	new_buf = tty->nextbuf;
	if(!new_buf)
		new_buf = grow_tty_buf(tty);
	queue_to_ldisc(tty->buf);
	tty->buf = newbuf;
}

and "free" most of the time can simply queue the buffer back to the tty.
That degenerates into flip buffers in good conditions..

> to the line discipline. This amounts to ~3600 sk_buff
> allocations per second at 115200bps.

Ethernet packets at 1500bytes arriving at 100Mbit is rather higher than
that, and the processing demands are higher too