Re: [Xen-users] System seams slower with Xenified kernel and xend dies with SIG 15

[Gabriel Rossetti <rossettigab@xxxxxxxxxxx>]

:-) Don't worry for the post-on-post thing.

Ok, That may be it then. I rechecked some more and it does (the ATI driver) try to compile something, and it says that
the arch is unknown, it seams to be from the Xen compatible processor setting in  the kernel config, CONFIG_X86_XEN=y
as opposed to the usual CONFIG_X86_PC. But you are probably right, makes sense. I'll keep on looking as pure curiosity :-)

Thanks again,
Gabriel


Petersson, Mats wrote:

-----Original Message-----
From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx 
[mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of 
Petersson, Mats
Sent: 02 August 2006 11:09
To: Gabriel Rossetti; xen-users@xxxxxxxxxxxxxxxxxxx
Subject: RE: [Xen-users] System seams slower with Xenified 
kernel and xend dies with SIG 15

    

-----Original Message-----
From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx 
[mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of 
Gabriel Rossetti
Sent: 02 August 2006 10:55
To: xen-users@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-users] System seams slower with Xenified 
kernel and xend dies with SIG 15

Ok, but wouldn't the OS take care of that? I don't think that 
the driver
does any
address translations, it would make no sense, it would use virtual
addresses and the OS, in my case a Xenified
linux kernel, takes care of translations. I suspect that some of the
changes made for Xen is the memory management, no?
      

Yes, but some of the changes in the Xenified kernel is to 
add/change the
code in drivers... And since the binary for the ATI (or 
nVidia) drivers
aren't source-code, they don't get the new code by recompiling the
kernel... 

    

If so then I would make sense that it stays transparent so that
everything would still work and
not have to recompile everything like in Denali. At least 
that's what I
think, from what I saw in
an OS class, and that I had to implement an OS's memory 
managment, but I
may be wrong. Also,
my binary Intel ipw3945 wireless drivers work fine, so I don't think
that is it, but then again, I may
be wrong. From my light investigation I think it's a path 
      

problem, it
    

can't find something apparently,
and I don't get why not. I'll have to look at it more when I 
find the time.
      

Maybe the wireless driver is more "well-behaved". 
    

Thinking another few seconds about it, I think one main difference is
that a wireless driver doesn't put physical addresses within the packet
for the PCI-device to use as addresses for other things, it just says
"Here's a packet, go send it" to the DMA-API, which works fine. 

Graphics drivers will have things like:

Here's a DMA-buffer:
	<BitBlt from(0,0,100,100) src="" address),
to(100,100,200,200) dest=(some other address)>

The addresses for src and dest need to be translated correctly to
machine physical addresses. The natural operation here is to just look
up the virtual address and translate it to a physical one - but the
normal OS doesn't understand the fact that there are two types of
physical address - one that it uses internally, and another one for
external devices... 

Sorry for the post-on-post thing... 

--
Mats
  

--
Mats
    

Gabriel



Petersson, Mats wrote:
      

Can't comment on xend dieing, but any binary driver would 
        

be unlikely to
      

work in Xenified kernel, since the Xenified kernel changes 
        

some of the
      

things that a driver needs to do when it translates 
        

memory addresses
    

from virtual to physical - there are now two different 
        

types of physical
      

address: pseudo-physical, which is what the OS sees, and machine
physical, which is what the PROCESSOR sees. If you have a 
        

Dom0 that has
      

512MB of RAM, it will not necessarily have all it's memory from
0..512MB, but it may actually be located anywhere Xen likes 
        

it to be...
      

[Dom0 is most likely starting somewhere low, since it's 
        

loaded early -
      

but that's just luck, rather than planned for]. Machine 
        

physical is
    

needed for the PCI (PCIe == PCIx == AGP == PCI in this case 
        

- they are
      

just different hardware implementations of the same 
        

protocol) so that
      

the card can access memory directly, and for sure all 
        

modern graphics
      

cards have direct memory access capabilities (and most 
        

likely doesn't do
      

much other than a standard 15 year old VGA card if you 
        

don't use these
      

capability). 


--
Mats


  
        

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