[syslinux] Etherboot & pxelinux (was: thank you)

Josef Siemes jsiemes at web.de
Fri Feb 8 01:54:30 PST 2002


"H. Peter Anvin" <hpa at zytor.com> schrieb am 07.02.02:
> Josef Siemes wrote:
> > 
> > That's a different point - if the high level bits in pxelinux were in
> > C I'd have done something there. 
> At some point I might do a C-based bootloader -- probably an actually
> working implementation of Genesis -- but the *LINUX series are designed to
> be as small as possible, which means that going to C, using a 16-bit C
> compiler, isn't really practical -- free 16-bit compilers are uniformly
> nonoptimizing.

It's just some idea to have it C-based. I think of it as some asm
routines with C interface, so if you want to deal with A20 handling
or some other complicated task you'd still have asm, some high-level
processing (like e.g. parsing the config file) would be in C.
I think this is how etherboot handles this.

> Since you have to turn off blksize anyway if you want to support early PXE
> stacks, how much does this matter?

It would be nice to have this option (e.g. set via a DHCP option), 
usually this would be turned off, and only activated for clients were
one knows that it works.

> Now, questions:
> a) Is this worthwhile enough that I should spend time on it?  How much do
> you think it will buy you?

Since we have some of the clients booting over an 1 MBit line it 
would save some seconds booting these. It's just an idea and 
nice to have, but it also works without blksize. Since you already
told me a while ago that blksize support is quite much work I think
it isn't needed. Maybe you could keep blksize in mind while 
restructuring the code.

> b) Should we aim for an even larger blksize by default?  What about PXE
> stacks that don't handle defragmentation correctly?

I think that the standard behaviour should stay with 512 Bytes blksize
(read: without the blksize option at all). This works reliably with 
almost all PXE stacks.

We made some measurements about different blksizes at different bandwidth, 
and it turned out that you gain few with LAN lines, but the lower the bandwith the more you gain with higher blksize. So higher blksize is only needed if you have some WAN line with low bandwidth.


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