Re: struct ifnet and ifaddr handling [was: Re: Making global variables of if.c MPSAFE]

[Masao Uebayashi <uebayasi%gmail.com@localhost>]

On Tue, Nov 18, 2014 at 11:24 AM, Ryota Ozaki <ozaki-r%netbsd.org@localhost> wrote:
> First I'm not against restructuring, though I hoped minimum
> restructuring on non-performance-sensitive paths.

My understanding is that, non-performance-sensitive paths (e.g.
ioctl()'s) also touches performance-sensitive data structures (e.g.
ifnet list), that is the problem.  Non-performance-sensitive paths
have to be more careful to not disturb performance-sensitive data
structures and paths.  For ioctl()'s, they have to allocate
kernel-wired memory to not sleep (via copyout()) while iterating
performance-critical ifnet list.  Thus I don't think you can avoid
restructuring those codes.

(I'd want to also encourage you to *not* become too nervous about
changing those codes.  Let's progress bravely and rely on high-quality
NetBSD "end" users for testing. :)

> BTW, do you think we eventually introduce "all packet processing in
> a LWP context"-like restructuring? I'm inclined to run Layer2 and bpf
> in softint. If we also end up doing so, I want to do it early.
> Of course, we have to address performance issues somehow at some point
> though.
>
> Thanks,
>   ozaki-r
>
>>
>> Dave
>>
>> --
>> David Young
>> dyoung%pobox.com@localhost    Urbana, IL    (217) 721-9981