[openbeosnetteam] Re: kernel- or user-land [Was: Change of heart...]
- From: Ksyu & Dima <k2d2@xxxxxxxxxxxxxxx>
- To: openbeosnetteam@xxxxxxxxxxxxx
- Date: Tue, 05 Feb 2002 19:04:47 -0400
Hi,
j-schwerer@xxxxxxx wrote:
> Hi,
>
>
>>what worries me about such a change that in the future (when the stack =
>>
>
>>moves into the kernel) we will have to rewrite a lot of stuff (I am =
>>
>
>>afraid that even if the plugin approach is taken the code will not be =
>>
>
>>iimediately reusable).
>>
>
> As I put it in an earlier mail I don't clearly understand how much of a
> difference that brings on a network stack (in which I would expect most o=
> f the
> code to be protocol-related and "anywhere-land" independant?). Therefore =
> Id'
> really appreciate if someone would *clearly* (clearly, as in "clearly det=
> ailed
> with examples for the dummies" =3DP) explain WHY there would be "a lot of=
> stuff"
> to rewrite.
>
>
The main difference is in the performance: for a user-land stack a
packet processing will require three context switches:
nic recives a packet; driver forwards it to the net-server (kernel);
net-server receives a packet; does its magic; sends a reply (let's
assume that is does) (user-land);
driver receives a packet and forwards it to the nic (kernel);
if the final destination of all packets is some application-layer
talking server (like http server) it may or may not make a difference.
Does anybody know any details on performance of network application
with different types of networks stacks?
One thing to keep in mind though is that user-land stack will share
cpu time will other applications that happen to run on this CPU.
For lower levels (arp, icmp, etc) it will make a difference as the
user-land model adds additional context switches (for the kernel-land
stack no context switches are required).
Now last, but not least, Be themselves in the end discarded the
user-land stack in favor of kernel-land one.
>>At this point it doesn't really matter whether one should learn kernel =
>>
>
>>API or learn how to write network server plug-ins (IMHO the difference =
>>
>
>>will not be that big).
>>
>
> IMHO I also think there shouldn't be that big a difference. So I am getti=
> ng
> even more confused now when you say there would be a lot to rewrite ^_^
>
>
The difference I meant is in what model we will code for; It may not
necessary be the case that the code written for one model is easily
ported to another one.
>>With the approach that was discussed before (plug-in architecture) the =
>>
>
>>"entry requirements" depend not as much on ones understanding of =
>>
>
>>kernel structures and API, but rather on understanding of networking =
>>
>
>>protocols and algorithms to implement them, which will be the same in =
>>
>
>>either case.
>>
>
> Jean
All i'm trying to do is consider both options and find the one which
would be the best to implement.
Dmitri
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