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Re: Support for many devices in the kernel (Was 802.1q)

To: mitch@xxxxxxxxxx (Mitchell Blank Jr)
Subject: Re: Support for many devices in the kernel (Was 802.1q)
From: Steve Whitehouse <steve@xxxxxxxxxxxxxx>
Date: Wed, 7 Jun 2000 13:15:50 +0100 (BST)
Cc: greearb@xxxxxxxxxxxxxxx (Ben Greear), hadi@xxxxxxxxxx (jamal), saw@xxxxxxxxxxxxx (Andrey Savochkin), rob@xxxxxxxxxxx, buytenh@xxxxxxx, netdev@xxxxxxxxxxx, gleb@xxxxxxxxxxxxxxxxxxxxx
In-reply-to: <20000607050813.H7740@sfgoth.com> from "Mitchell Blank Jr" at Jun 07, 2000 05:08:13 AM
Organization: ChyGywn Limited
Reply-to: Steve Whitehouse <Steve@xxxxxxxxxxx>
Sender: owner-netdev@xxxxxxxxxxx
> 
> Ben Greear wrote:
> > As someone pointed
> > out (sorry, deleted the mail), other than the dev_get_by[index/name], there
> > is one other place, in the IP stack, that ***may*** be called often that
> > walks the device list.
> 
> Well there are others, but they're in weird protocols (decnet, rose, netrom).
> I doubt we'll ever need to support large numbers of devices running
> those protocols.  If we want them to perform well even with lots of
> devices running other protocols we can have them keep their own list
> of the net_devices they are using.  IPX does this, for instance.
> 

As you suggest the places that DECnet uses the device list are few. If
you want me to put together a patch which make DECnet use its own list of
devices let me know... I think the only place it will make any real 
difference is in the bind() call where we walk the DECnet devices to check
one of them has the local address that we are bind()ing to.

> > 3)  Investigate the linear walk in IP land.
> 
> Someone should try putting a counter there to report who many times that
> code actually gets hit on normal use.
> 
> > One thing I didn't bring up
> > before: If the IP code needs to walk all 'routable things', then even
> > if VLANs are not devices, this code will probably need to walk them.
> 
> Exactly right.  It specifically searches each device and for each
> one linearly searches all the "ifa" structures on the device.
> So if all the VLANs were using the same net_device there would
> still be as many ifa's total.  In fact, the situation would be far,
> far worse since there are a lot of other places in the ipv4 code
> that the ifa list on a particular device gets searched.
> 
> -Mitch
> 

I think the same applies to DECnet. The routing in DECnet is more or less
copied from IPv4, so what works for IP will probably work with DECnet too,

Steve.


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