Re: [PATCH v8 0/3] Split logging functionality out of EAL

[Thomas Monjalon <thomas@monjalon.net>]

11/08/2023 14:59, Bruce Richardson:
> On Fri, Aug 11, 2023 at 02:46:13PM +0200, David Marchand wrote:
> > On Wed, Aug 9, 2023 at 3:36 PM Bruce Richardson
> > <bruce.richardson@intel.com> wrote:
> > >
> > > There is a general desire to reduce the size and scope of EAL. To this
> > > end, this patchset makes a (very) small step in that direction by taking
> > > the logging functionality out of EAL and putting it into its own library
> > > that can be built and maintained separately.
> > >
> > > As with the first RFC for this, the main obstacle is the "fnmatch"
> > > function which is needed by both EAL and the new log function when
> > > building on windows. While the function cannot stay in EAL - or we would
> > > have a circular dependency, moving it to a new library or just putting
> > > it in the log library have the disadvantages that it then "leaks" into
> > > the public namespace without an rte_prefix, which could cause issues.
> > > Since only a single function is involved, subsequent versions take a
> > > different approach to v1, and just moves the offending function to be a
> > > static function in a header file. This allows use by multiple libs
> > > without conflicting names or making it public.
> > >
> > > The other complication, as explained in v1 RFC was that of multiple
> > > implementations for different OS's. This is solved here in the same
> > > way as v1, by including the OS in the name and having meson pick the
> > > correct file for each build. Since only one file is involved, there
> > > seemed little need for replicating EAL's separate subdirectories
> > > per-OS.
> > 
> > Series applied, thanks Bruce for this first step.
> > 
> > As mentionned during the maintainers weekly call yesterday, this is
> > only a first "easy" step but, thinking of next steps, more splitting
> > may not be that easy.
> 
> I took a look after doing this patchset to try and find more easy to
> extract parts, but did not find many. The EAL is pretty intertwined now.
> As I look at it, there are really two ways to try and dis-entangle it - 
> bottoms-up or top-down. This patchset is an example of the former, taking a
> logical set of related APIs and pulling them out into a separate library
> that EAL can depend upon. There may be some other API-sets like this we can
> pull out, but in my search I didn't find any.

A small thing to easily separate is rte_bitmap.

> The other tops-down approach may be worth looking at too. We can try and
> take the top-level EAL init function and separate it out into a separate
> initialization library (which may be called "EAL" with the rest being
> called something else). I have not tried this approach to see how it goes,
> but pulling out the init may allow further dis-entangling of other parts of
> EAL.

I agree we should start with separating the init logic.
I would call it rte_init. We may need rte_opts for command line parsing.
I think the name EAL should be kept for the low-level functions,
abstracting differences between OS, CPU and toolchains.

Next steps would be to try to separate memory and CPU management
in 2 different libraries.
We'll need to decide whether rte_service is part of the CPU management.
Same question for multiprocess communication rte_mp and rte_keepalive.
I suppose we can keep IRQ and threading in EAL.
VFIO may be managed in a separate library perhaps.

Once we do that, the low-level libraries like log, kvargs and telemetry
can depend on EAL, being the very low-level common denominator.
The trace subsystem can probably become a separate library as well.

In a later step, we can think about bus and device management.

And the ideal would be to extract tailq, once all logic is out of EAL.

How does it sound?