netdev - Re: [PATCH net-next v2 1/2] net: sched: pie: refactor code

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Date:   Wed, 1 Jan 2020 12:05:50 +0530
From:   Leslie Monis <lesliemonis@...il.com>
To:     Stephen Hemminger <stephen@...workplumber.org>
Cc:     Gautam Ramakrishnan <gautamramk@...il.com>,
        Linux NetDev <netdev@...r.kernel.org>,
        "Mohit P. Tahiliani" <tahiliani@...k.edu.in>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        "David S . Miller" <davem@...emloft.net>,
        Dave Taht <dave.taht@...il.com>,
        Toke Høiland-Jørgensen <toke@...hat.com>,
        "Sachin D . Patil" <sdp.sachin@...il.com>,
        "V . Saicharan" <vsaicharan1998@...il.com>,
        Mohit Bhasi <mohitbhasi1998@...il.com>
Subject: Re: [PATCH net-next v2 1/2] net: sched: pie: refactor code

On Tue, Dec 31, 2019 at 10:34 PM Stephen Hemminger
<stephen@...workplumber.org> wrote:
>
> On Tue, 31 Dec 2019 16:53:15 +0530
> gautamramk@...il.com wrote:
>
> > From: "Mohit P. Tahiliani" <tahiliani@...k.edu.in>
> >
> > This patch is a precursor for the addition of the Flow Queue Proportional
> > Integral Controller Enhanced (FQ-PIE) qdisc. The patch removes functions
> > and structures common to both PIE and FQ-PIE and moves it to the
> > header file pie.h
> >
> > Signed-off-by: Mohit P. Tahiliani <tahiliani@...k.edu.in>
> > Signed-off-by: Sachin D. Patil <sdp.sachin@...il.com>
> > Signed-off-by: V. Saicharan <vsaicharan1998@...il.com>
> > Signed-off-by: Mohit Bhasi <mohitbhasi1998@...il.com>
> > Signed-off-by: Leslie Monis <lesliemonis@...il.com>
> > Signed-off-by: Gautam Ramakrishnan <gautamramk@...il.com>
> > ---
> >  include/net/pie.h   | 400 ++++++++++++++++++++++++++++++++++++++++++++
> >  net/sched/sch_pie.c | 386 ++----------------------------------------
> >  2 files changed, 415 insertions(+), 371 deletions(-)
> >  create mode 100644 include/net/pie.h
> >
> > diff --git a/include/net/pie.h b/include/net/pie.h
>
>
> Adding lots of static functions in a header file is not the way
> to get code reuse in Linux kernel. It looks like you just did
> large copy/paste from existing sch_pie.c to new header file.
>
> You can use reuse data structures and small 'static inline' functions in a header file.
> But putting code like drop_early in a header file is not best
> practice.
>
> You need to create a real kernel API for this kind of thing
> by making a helper module which is reused by multiple places.

Hi Stephen,

Thanks for the feedback.

We did initially think of using EXPORT_SYMBOL to reuse large
functions like drop_early. However, we wanted to keep our
changes consistent with the existing Codel/FQ-Codel
implementation, and so we decided to move the functions
common to sch_pie.c and sch_fq_pie.c (the module we wish to
add) to pie.h, as done by codel and fq_codel.

Since you mentioned that this is not best practice, we're thinking
of simply exporting the required symbols from sch_pie.c and not
making an external helper module. We'll then create a module
dependency for sch_fq_pie.c on sch_pie.c. We'll still add
the pie.h header file to keep structures and small inline functions.

Would you recommend we go ahead with this?

Thanks,
Leslie