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

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Message-ID: <20190226075057.1e76bba7@shemminger-XPS-13-9360>
Date:   Tue, 26 Feb 2019 07:50:57 -0800
From:   Stephen Hemminger <stephen@...workplumber.org>
To:     Leslie Monis <lesliemonis@...il.com>
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 Tue, 26 Feb 2019 13:50:46 +0530
Leslie Monis <lesliemonis@...il.com> wrote:

> 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.

Thanks for answering. Looks good