linux-kernel - Re: [PATCH v1 09/12] dyndbg: add trace destination field to

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Message-ID: <CAJfuBxzuEjp+PK75Upa7HoAJMs-Bx49knfjoEBTJXPsXkTDijw@mail.gmail.com>
Date:   Mon, 13 Nov 2023 12:49:19 -0700
From:   jim.cromie@...il.com
To:     Łukasz Bartosik <lb@...ihalf.com>
Cc:     Jason Baron <jbaron@...mai.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Kees Cook <keescook@...omium.org>,
        Douglas Anderson <dianders@...omium.org>,
        Guenter Roeck <groeck@...gle.com>,
        Yaniv Tzoreff <yanivt@...gle.com>,
        Benson Leung <bleung@...gle.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Vincent Whitchurch <vincent.whitchurch@...s.com>,
        Pekka Paalanen <ppaalanen@...il.com>,
        Sean Paul <seanpaul@...omium.org>,
        Daniel Vetter <daniel@...ll.ch>, linux-kernel@...r.kernel.org,
        upstream@...ihalf.com
Subject: Re: [PATCH v1 09/12] dyndbg: add trace destination field to _ddebug

On Sun, Nov 12, 2023 at 9:29 AM Łukasz Bartosik <lb@...ihalf.com> wrote:
>
> pt., 10 lis 2023 o 20:37 <jim.cromie@...il.com> napisał(a):
> >
> > On Fri, Nov 10, 2023 at 7:52 AM Łukasz Bartosik <lb@...ihalf.com> wrote:
> > >
> > > sob., 4 lis 2023 o 02:39 <jim.cromie@...il.com> napisał(a):
> > > >
> > > > On Fri, Nov 3, 2023 at 7:10 AM Łukasz Bartosik <lb@...ihalf.com> wrote:
> > > > >
> > > > > Add trace destination field (trace_dst) to the _ddebug structure.
> > > > > The trace destination field is used to determine output of debug
> > > > > logs when +T is set. Setting trace_dst value to 0 (default) enables
> > > > > output to prdbg and devdbg trace events. Setting trace_dst value to
> > > > > a value in range of [1..255] enables output to trace instance.
> > > >
> > > >
> > > > should we do some expectation setting here ?
> > > > 255 is something of a promise to more than tom,dick,harry.
> > > > 16-64 is more suggestive of a limited resource,
> > > > might encourage more judicious use.
> > > >
> > >
> > > How about making it configurable in kernel Kconfig with default value
> > > set to 16 or 32 ?
> > >
> >
> > given the general dislike of extra knobs, it's not the battle I would choose.
> > ISTM we could start small, add bits later (if needed)
> > maybe 16 is too parsimonious; esp if DRM wants multiple instances per
> > driver (device?)
> >
>
> If we don't want the extra config knob then I would opt for 64.

I think I could live with that.
And I dont foresee other uses for spare bits atm.