[genode] Does order matter?

[jaeyong yoo]

Hi Norman,

I thought I saw such a thing, but probably (almost 100% I guess) I was
making a mistake :)

Thanks always for the kind answer,
Jaeyong

On Mon, Jan 21, 2013 at 9:12 PM, Norman Feske
<norman.feske at ...1...>wrote:

> Hi Jaeyong,
>
> > GENODE_RPC_INTERFACE(Rpc_func_a, Rpc_func_b);
> ...
> >
> > GENODE_RPC_INTERFACE(Rpc_func_b, Rpc_func_a); /* the order of
> > func_a and func_b is reversed */
> >
> > Do the above two RPC call definitions are equally OK?
>
> yes. Functionality-wise they are the same.
>
> Under the hood of the RPC framework, the order determines the assignment
> of opcodes to the RPC functions of an RPC interface. Thereby it
> implicitly defines the sequence of how the opcode of an incoming RPC
> request is matched against the different RPC functions on the server
> side. So strictly speaking, the order influences the performance of
> dispatching an incoming RPC call. For example, if a RPC function is the
> third function specified in the RPC interface, the server will always
> compare the incoming opcode against the first end second function before
> successfully matching the third. So the dispatching of the third RPC
> function carries the overhead for those two negative checks. That said,
> I think that the effect is negligible. Given the total costs involved in
> performing an RPC call (context switches, IPC path, security checks),
> changing the order should hardly make any measurable difference. If you
> find otherwise, I'd be highly interested in investigating. ;-)
>
> Cheers
> Norman
>
> --
> Dr.-Ing. Norman Feske
> Genode Labs
>
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