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

[Seth Goldberg]

On Apr 26, 2012, at 6:46 AM, Bean <address@hidden> wrote:

> On Thu, Apr 26, 2012 at 12:59 PM, Seth Goldberg
> <address@hidden> wrote:
>> 
>> 
>> 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).
> 
> Hi,
> 
> Well, it's possible that different uefi implementation has different
> issues, but at least this method works quite well for the machines I
> tested. I can send you a test program if you want to give it a try.

  Sure!  Thanks!

  --S


> 
> -- 
> Best wishes
> Bean
> 
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