netdev - Re: [PATCH net-next v3 0/7] net: sched: pie: align PIE implementation with RFC 8033

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Date:   Tue, 26 Feb 2019 13:50:46 +0530
From:   Leslie Monis <lesliemonis@...il.com>
To:     Stephen Hemminger <stephen@...workplumber.org>
Cc:     davem@...emloft.net, netdev@...r.kernel.org,
        "Mohit P . Tahiliani" <tahiliani@...k.edu.in>,
        Dave Taht <dave.taht@...il.com>,
        Jamal Hadi Salim <jhs@...atatu.com>
Subject: Re: [PATCH net-next v3 0/7] net: sched: pie: align PIE
 implementation with RFC 8033

On Mon, Feb 25, 2019 at 04:38:11PM -0800, Stephen Hemminger wrote:
> On Tue, 26 Feb 2019 00:39:54 +0530
> Leslie Monis <lesliemonis@...il.com> wrote:
> 
> > The current implementation of the PIE queuing discipline is according to the
> > IETF draft [http://tools.ietf.org/html/draft-pan-aqm-pie-00] and the paper
> > [PIE: A Lightweight Control Scheme to Address the Bufferbloat Problem].
> > However, a lot of necessary modifications and enhancements have been proposed
> > in RFC 8033, which have not yet been incorporated in the source code of Linux.
> > This patch series helps in achieving the same.
> > 
> > Performance tests carried out using Flent [https://flent.org/]
> > 
> > Changes from v2 to v3:
> >   - Used div_u64() instead of direct division after explicit type casting as
> >     recommended by David
> > 
> > Changes from v1 to v2:
> >   - Excluded the patch setting PIE dynamically active/inactive as the test
> >     results were unsatisfactory
> >   - Fixed a scaling issue when adding more auto-tuning cases which caused
> >     local variables to underflow
> >   - Changed the long if/else chain to a loop as suggested by Stephen
> >   - Changed the position of the accu_prob variable in the pie_vars
> >     structure as recommended by Stephen
> > 
> > Mohit P. Tahiliani (7):
> >   net: sched: pie: change value of QUEUE_THRESHOLD
> >   net: sched: pie: change default value of pie_params->target
> >   net: sched: pie: change default value of pie_params->tupdate
> >   net: sched: pie: change initial value of pie_vars->burst_time
> >   net: sched: pie: add more cases to auto-tune alpha and beta
> >   net: sched: pie: add derandomization mechanism
> >   net: sched: pie: update references
> > 
> >  include/uapi/linux/pkt_sched.h |   2 +-
> >  net/sched/sch_pie.c            | 107 ++++++++++++++++++++-------------
> >  2 files changed, 66 insertions(+), 43 deletions(-)
> 
> Are you concerned at all that changes to default values might change
> expected behavior of existing users?

Hi Stephen,

As Dave mentioned, the changes which we have made do not really change the
behaviour of the aqm drastically. Our performance tests show that these changes
improve performance without any side-effects. So existing users (if there are
any) should not be negatively affected in any way.

Leslie