re: MP-safe ifnet with psz & psref

[matthew green <mrg%eterna.com.au@localhost>]

Thor Lancelot Simon writes:
> I do not think you should do any extra work to support kvm grovelling.

existing tool functionality should not be broken, however.  the
netstat -i groveller code should be either updated to the new
method or converted to a real sysctl, though the current work
around would be ok for now.  simply breaking netstat -i is not
an acceptable solution.


.mrg.

> On Tue, May 10, 2016 at 12:07:12PM +0900, Ryota Ozaki wrote:
> > On Thu, Apr 28, 2016 at 4:04 PM, Ryota Ozaki <ozaki-r%netbsd.org@localhost> wrote:
> > > Hi,
> > >
> > > This proposal is the first step toward making interfaces
> > > (struct ifnet) MP-safe; it applies psz and psref to ifnet
> > > and ifnet_list to safely look up ifnets from ifnet_list
> > > and safely remove an ifnet.
> > >
> > > Here is a patch:
> > >   http://www.netbsd.org/~ozaki-r/psref-ifnet.diff
> > 
> > I restored the original ifnet_list because the change broke
> > netstat -i (kvm(3)). So we now maintain two ifnet lists while
> > the original list is only added/removed elements and not
> > referenced by say IFNET_FOREACH. It's redundant but its overhead
> > is negligible and it's the easiest way to keep backward
> > compatibility. Of course, ideally we should kill kvm(3) users
> > and remove the original list, but it's not now, I think.
> > 
> > Objection?
> > 
> >   ozaki-r
> > 
> > >
> > > One concern is m_reclaim that can be run in hardware
> > > interrupt and so the patch skips if_drain if it's
> > > running in hardware interrupt because pserialize is
> > > basically designed used in lwp or softint (and now
> > > psref is used with IPL_SOFTNET). Is there a better
> > > solution?
> > >
> > > And any other suggestions and comments would be
> > > appreciated.
> > >
> > > Thanks,
> > >   ozaki-r
> > >
> > > P.S. From today for ten days, I'll be unable to use
> > > my main development machines, I wouldn't be able to
> > > update and test patches reflected your feedbacks enough.
> 
> -- 
>   Thor Lancelot Simon	                                     tls%panix.com@localhost
> 
>   "We cannot usually in social life pursue a single value or a single moral
>    aim, untroubled by the need to compromise with others."      - H.L.A. Hart
>