[syslinux] Very slow download with pxelinux > 4.07 on specific hardware

[H. Peter Anvin]

On 02/25/2014 07:45 AM, H. Peter Anvin wrote:
> On 02/25/2014 07:07 AM, Eric PEYREMORTE wrote:
>> I did some additional tests :
>>
>> On a dell optiplex 380, i disabled internal nic, added a 3com 905c tx
>> external pci nic : very slow too.
>> On a dell 740(which is always fast), i put the 3com to be sure : very fast.
>>
>> So it seems it is not related to the nic itself. To be sure it wasn't
>> just one failing computer i tested several 380.
>>
>> I tried disabling several features in bios, like Execute Disable,
>> multicore support, speedstep... Nothing helped.
>>
>> I thought at the beginning it was an efi problem (althought i use it in
>> bios mode), but on optiplex 7010 which is efi based too, i don't have
>> the problem...
>>
>> I used 6.03pre2 for this test.
>>
>> As i said previously no problem before version 5.00.
>>
> 
> OK, this is extremely surprising.  Normally the NIC card BIOS is what
> matters for PXE performance, but it sounds like in your case there is
> something going on in the main BIOS that is causing problems.
> 

What I'm at a loss for is *how* that would happen.  The biggest
difference that I can think of is in the layout of the memory, but that
shouldn't cause that kind of thing.

Sending the wireshark trace might be useful, it certainly can't hurt.

If there is a lost interrupt somehow that might explain the problem, but
that shouldn't be related to Syslinux 4 vs 5/6 in any way...

	-hpa