Re: [PATCH 07/17] net: convert sock.sk_refcnt from atomic_t to refcount_t

[Peter Zijlstra]

On Tue, Mar 21, 2017 at 04:51:13PM -0700, Kees Cook wrote:
> On Tue, Mar 21, 2017 at 2:23 PM, Eric Dumazet <eric.dumazet@xxxxxxxxx> wrote:

> > Unfortunately there is no good test simulating real-world workloads,
> > which are mostly using TCP flows.
> 
> Sure, but there has to be _something_ that can be used to test to
> measure the effects. Without a meaningful test, it's weird to reject a
> change for performance reasons.

This. How can you optimize if there's no way to actually measure
something?

> > Most synthetic tools you can find are not using epoll(), and very often
> > hit bottlenecks in other layers.
> >
> >
> > It looks like our suggestion to get kernel builds with atomic_inc()
> > being exactly an atomic_inc() is not even discussed or implemented.
> 
> So, FWIW, I originally tried to make this a CONFIG in the first couple
> passes at getting a refcount defense. I would be fine with this, but I
> was not able to convince Peter. :) However, things have evolved a lot
> since then, so perhaps there are things do be done here.

Well, the argument was that unless there's a benchmark that shows it
cares, its all premature optimization.

Similarly, you wanted this enabled at all times because hardening.