Re: RFC: UEFI/PXE and emulating grub-legacy-uefi-hacked behaviour

[Seth Goldberg]

On Apr 25, 2012, at 11:22 PM, Bean <address@hidden> wrote:

> On Thu, Apr 26, 2012 at 12:10 PM, Seth Goldberg
> <address@hidden> wrote:
>>  How does this work around the issue?  I'm not seeing it -- we call SNP 
>> directly.  We don't go through UDP or any other upper layers in efinet.  
>> When I did the investigation, I removed ALL other consumers of SNP manually 
>> via the efi shell before loading GRUB 2 and still saw packet loss.
> 
> Hi,
> 
> Normal OS has interrupt handler that removes the packet from nic
> buffer as soon as possible, but grub2 is basically single thread and
> use pull mode. So we should make the pulling loop as short as
> possible. In async mode, if a packet is not found, it has to returned
> to upper layer and retry, while in sync mode, the loop is inside the
> driver which make it more efficient. It's something like reading 100
> bytes from disk is much faster than 100 x 1 byte.
> 

  Marginally.  We still need to handle that packet inside grub once it is 
received.  Besides, modern nic hardware has receive rings and overrun is rare 
especially with non-pipelined tftp (unless there is a ton of broadcast or 
unicast packets sent to the client while in grub which is unlikely in practice, 
so I'm not seeing where the real benefit is here.  I can definitely understand 
your finding inefficiencies in the uefi udp-snp (or in systems I've seen it's 
more like UDP-MNP-SNP), so no argument there, but for grub 2, it's already 
using the lowest level interface it can (without calling undi directly).

 --S

> 
> -- 
> Best wishes
> Bean
> 
> _______________________________________________
> Grub-devel mailing list
> address@hidden
> https://lists.gnu.org/mailman/listinfo/grub-devel