Re: CVS commit: src/sys

[Ryota Ozaki <ozaki-r%netbsd.org@localhost>]

On Tue, May 14, 2019 at 10:54 PM Greg Troxel <gdt%lexort.com@localhost> wrote:
>
> Ryota Ozaki <ozaki-r%netbsd.org@localhost> writes:
>
> > On Tue, May 14, 2019 at 2:31 AM Jason Thorpe <thorpej%me.com@localhost> wrote:
> >>
> >>
> >>
> >> > On May 13, 2019, at 7:17 AM, Greg Troxel <gdt%lexort.com@localhost> wrote:
> >> >
> >> > 2) Your option 2 seems to involve two things at once:
> >> >
> >> >  - migration to lwp_specificadata
> >> >  - using DEBUG instead of DIAGNOSTIC to control the leak check feature
> >> >
> >> > I do not understand why changing the nature of the implementation is
> >> > linked to how it is enabled.
> >>
> >> I think Ozaki-san saying that the 3% performance hit only happens
> >> when lwp_specificdata is used, and hence that it would need to be
> >> wrapped in DEBUG rather than DIAGNOSTIC.
>
> Now this is all making sense.
>
> >> The original negligible-impact implementation did NOT use
> >> lwp_specificdata, and thus was fine for DIAGNOSTIC.  I believe
> >> Ozaki-san's preference is to use *this* implementation so that it
> >> can be exposed to a wider audience.  The lwp_specificdata approach
> >> was only explored after someone else suggested a preference for it.
> >>
> >> At least, that's my understanding of the situation.
> >
> > Yes, your understanding is correct.  Thank you for the clarification.
>
> So having a check under DIAGNOSTIC that you more or less can't measure
> sounds just fine to me.  I only meant to object to a 3% slowdown under
> DIAGNOSTIC.
>
> And, if someone is inclined, having better checks with meaurable
> slowdown under DEBUG sounds ok too, but my revised understanding is
> unclear on whether that's helpful.  (But I am only trying to keep
> performance under DIAGNOSTIC high; I am unconcerned about DEBUG and
> don't need to understand.)

I've proposed another implementation a few days ago (*).  That provides
useful information for debugging in exchange for expensive overhead.
It is enabled by PSREF_DEBUG.

(*) https://mail-index.netbsd.org/tech-kern/2019/05/10/msg025049.html

  ozaki-r