netdev - RE: [patch net-next 5/5] mlxsw: spectrum: qdiscs: Support stats for PRIO qdisc

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Message-ID: <DB5PR05MB1895FDC0D523983C76B74AA5AC170@DB5PR05MB1895.eurprd05.prod.outlook.com>
Date:   Fri, 12 Jan 2018 09:29:22 +0000
From:   Nogah Frankel <nogahf@...lanox.com>
To:     Yuval Mintz <yuvalm@...lanox.com>, Jakub Kicinski <kubakici@...pl>
CC:     Jiri Pirko <jiri@...nulli.us>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "Ido Schimmel" <idosch@...lanox.com>, mlxsw <mlxsw@...lanox.com>,
        "jhs@...atatu.com" <jhs@...atatu.com>,
        "xiyou.wangcong@...il.com" <xiyou.wangcong@...il.com>
Subject: RE: [patch net-next 5/5] mlxsw: spectrum: qdiscs: Support stats for
 PRIO qdisc



> -----Original Message-----
> From: Yuval Mintz
> Sent: Friday, January 12, 2018 10:47 AM
> To: Jakub Kicinski <kubakici@...pl>
> Cc: Jiri Pirko <jiri@...nulli.us>; netdev@...r.kernel.org; Nogah Frankel
> <nogahf@...lanox.com>; davem@...emloft.net; Ido Schimmel
> <idosch@...lanox.com>; mlxsw <mlxsw@...lanox.com>; jhs@...atatu.com;
> xiyou.wangcong@...il.com
> Subject: RE: [patch net-next 5/5] mlxsw: spectrum: qdiscs: Support stats for PRIO qdisc
> 
> > > > Hm.  You you need this just because you didn't add the backlog
> > > > pointer to destroy?  AFAIK on destroy we are free to reset stats as
> > > > well, thus simplifying your driver...  Let me know if I
> > > > misunderstand.

The problem of doing it in destroy is when one qdisc is replacing another.
I want to be able to destroy the old qdisc to "make room" for the new one
before I get the destroy command for the old qdisc (that will come just
after the replace command for the new qdisc).
If I am saying that the destroy changes the stats, I need to save some data
about the old qdisc till I get the destroy command for it.

> > >
> > > This is meant exactly for the scenario where qdisc didn't get
> > > destroyed yet is no longer offloaded; E.g., if number of bands
> > > increased beyond What we can offload. So we can't reset the
> > > statistics in this case. [Although I might be the one to
> > > misunderstand you, as the 'not destroyed' was explicitly mentioned
> > > twice above]
> >
> > I was trying to take some liberty with handling of destroy but your
> > approach may actually end up being simpler.  I will withdraw my series
> > for now and reuse your new callback once this series lands.
> >
> > Do you have any objections to changing RED to behave more like prio
> > (and other qdiscs) in principle?

On the contrary, I think it is great.

> 
> From statistics' perspective? None.