netdev - Re: [net-next PATCH] dql: add a burst attribute

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Message-ID: <CA+mtBx85Qtbu-r=5Bfo9tp+VnX6D_RrQpvCV-R3VubZGOedydQ@mail.gmail.com>
Date:	Tue, 30 Sep 2014 21:44:50 -0700
From:	Tom Herbert <therbert@...gle.com>
To:	Jesper Dangaard Brouer <brouer@...hat.com>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	Florian Westphal <fw@...len.de>,
	Linux Netdev List <netdev@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	Daniel Borkmann <dborkman@...hat.com>,
	Jamal Hadi Salim <jhs@...atatu.com>,
	Alexander Duyck <alexander.duyck@...il.com>,
	John Fastabend <john.r.fastabend@...el.com>,
	Dave Taht <dave.taht@...il.com>,
	Toke Høiland-Jørgensen <toke@...e.dk>
Subject: Re: [net-next PATCH] dql: add a burst attribute

On Tue, Sep 30, 2014 at 2:46 PM, Jesper Dangaard Brouer
<brouer@...hat.com> wrote:
>
> On Tue, 30 Sep 2014 07:55:36 -0700
> Eric Dumazet <eric.dumazet@...il.com> wrote:
>
> > On Tue, 2014-09-30 at 16:31 +0200, Florian Westphal wrote:
> > > Eric Dumazet <eric.dumazet@...il.com> wrote:
> > > > If you feel not comfortable with "burst", rename it to whatever you
> > > > think is best.
> > > > But please, do not hard code magic 7 in your code.
> > >
> > > I had hoped that this 'magic' value could be removed
> > > completely, only using bql data for bulking decisions.
> >
> > But it is apparently not the case, since you guys decided to had it set
> > to 8, then to 7 later, based on experiments.
>
> The "magic" limit is only a conservative save guard.  We do plan to
> remove this completely.  That is the reason for not exporting this, as
> we want free-hands to remove this completely.
>
> Guess, I'll remove it completely now, so we can move on.
>
>
> I would like some off/on switch, exported to userspace, for disabling
> this bulking (then we don't need this conservative magic number).  How
> would that be done best?


I'd suggest to keep the packet limit as an unsigned. Default value is
infinity (-1UL), 0 turns it off, and other values are available if
someone really wants to tune this (for example, if BQL is disabled--
BQL limit is infinity). Export this as sys variable for the TX queue.

Tom

>
>
> --
> Best regards,
>   Jesper Dangaard Brouer
>   MSc.CS, Sr. Network Kernel Developer at Red Hat
>   Author of http://www.iptv-analyzer.org
>   LinkedIn: http://www.linkedin.com/in/brouer
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