LWN: Comments on "4K stacks - again"

FSF hardware info

dwheeler — Tue, 29 Nov 2005 17:31:44 +0000

The FSF has information about hardware with FLOSS drivers. Here's the FSF information on wireless cards. After looking around, I bought a Ralink RT2500-based card, an Asus WL-107G, for my lapttop -- it only cost $30, it supports b and g, and Ralink gives excellent support for FLOSS. There is active work to improve the driver further, too. No doubt there are others, but basing your purchasing decision on "what is supported" is usually a good plan when you can do it!

prism54

zooko — Sun, 20 Nov 2005 15:37:43 +0000

I use prism54 cards. The driver is GPLed (not counting proprietary firmware). It Just Works if you install Ubuntu. On the down side, you have to very carefully search to find a card which has a prism54 chipset. In fact, they might not be available any more. Also, I had persistent problems with performance at long range. My Mac Airport Extreme would buzz along just fine in that situation, but the prism54 system would stop working every minute or so.

wireless drivers

gravious — Fri, 18 Nov 2005 14:35:39 +0000

Aha,

To reply to myself. I just checked... The rt2500usb driver is in 2.6.15 in Dapper. I don't know when this went in, odd, I've been following the announcements quite closely. I tried it out and didn't get it working so it's back to 2.6.12 and ndiswrapper for now. Maybe somebody more masochistic and not with exam deadlines looming might give it a go. (Am I the only person who hates iwconfig? It is terse to the point of mute. I've also got that dropped connection problem using dhcp over wireless that people are complaining about with Fedora, SUSE, Ubuntu and elsewhere. It is a pain.)

regards,
Anto

4K stacks - again

Ross — Fri, 18 Nov 2005 07:03:52 +0000

But that was about the old Atheros driver which is distributed out-of-kernel, right? Or is that about the new driver... or are they in fact the same other than the firmware?

4K stacks - again

iabervon — Thu, 17 Nov 2005 21:47:45 +0000

NDISwrapper has no problem with 4K stacks. The problem is that the drivers it wraps can expect up to a 12K stack. Of course, Linux has never provided more than an 8K stack, so a given driver wouldn't necessarily work, but a number of popular drivers don't run out of stack even with only 4K.

4K stacks - again

fenrus — Thu, 17 Nov 2005 15:56:33 +0000

sounds right yes

not all the world is using ndiswrapper.. some people still have systems where they can use open source drivers...

Most of these calls have since been serialized?

fenrus — Thu, 17 Nov 2005 15:46:40 +0000

it goes like this; there is a key function that is used to submit IO
and DM and co need to change the IO a bit and then cause it to be submitted again

XFS -> function -> dm layer -> function -> dm layer -> function -> raid layer -> function -> scsi layer -> driver

(well theoretical example but you get the idea I hope)

in the new situation, instead of calling the function again, you return "do again" so it goes like

XFS -> function -> dm layer -|
function -> dm layer -|
function -> raid layer -|
function -> scsi layer -> driver

so the max depth is 4 (well real world is slightly more complex) independent on how often you layer this. In the old situation you could layer a lot and go really big (11 in the example, but just layer more and it goes higher)

Most of these calls have since been serialized?

snitm — Thu, 17 Nov 2005 15:33:52 +0000

Could someone elaborate on what it means to 'serialize' the historically long call chains associated with block devices + lvm2 + nfs + firewall, etc?

4K stacks - again

elicriffield — Thu, 17 Nov 2005 15:26:34 +0000

>Some distributions (e.g. Fedora Core and RHEL) have been shipping
>4K kernels for a while now

So NDISwrapper doesn't work with fedora core or RHEL? I don't use either so i don't know but that seems odd...

NDISwrapper - in user space?

mcatkins — Thu, 17 Nov 2005 14:22:08 +0000

I don't know much about this but...:

Wouldn't it be possible to move NDISwrapper into user space?

TAP, or somesuch, could shim the network device access. Getting
access to the hardware would be the tricky part, although it should
be fairly easy for USB dongles, and various mapping tricks
might work for 'normal' devices.

Of course, in userspace stack size is not much of an issue...

Martin

4K stacks - again

rjw — Thu, 17 Nov 2005 14:16:29 +0000

Couldn't the NDIS wrapper be run in userspace anyway?

wireless drivers

gravious — Thu, 17 Nov 2005 13:00:16 +0000

I second that.

I have a d-link dwl-g122 (h/w ver. b1) 802.11g usb thingy which uses one of those ralink rt2500 chip things and it would be sweet if this got into the mainline kernel - especially before Dapper is released. The source is here serialmonkey. Hope this helps somebody.

regards,
Anto

4K stacks - again

lacostej — Thu, 17 Nov 2005 10:24:28 +0000

There are still some questions on how the atheros driver was generated.
Not using a clean reverse engineering process it seems.

Atheros driver

JoeF — Thu, 17 Nov 2005 08:12:33 +0000

I am looking forward to a fully opensource Atheros driver in the kernel. I'm currently using the madwifi driver, which unfortunately has a closed part (better than nothing...)

wireless drivers

rfunk — Thu, 17 Nov 2005 06:41:15 +0000

I'm just looking forward to rt2500 support getting into the mainline
kernel. It's one of the few 54mb chipsets that has had a GPL driver (and
the OpenBSD crowd, sticklers for hardware openness, recommends those
cards), but so far it has to be added separately.

Hey, if a Broadcom driver is coming, that would have some positive
implications for Linksys WRT54G boxes. But I get no such host when
trying to link to http://bcm43xx.berlios.de/.