netdev - Re: [RFC net-next PATCH V3 0/2] qdisc bulk dequeuing and utilizing delayed tailptr updates

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Date:	Sat, 20 Sep 2014 00:28:52 +0300
From:	Dave Taht <dave.taht@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Jesper Dangaard Brouer <brouer@...hat.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Tom Herbert <therbert@...gle.com>,
	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	Florian Westphal <fw@...len.de>,
	Daniel Borkmann <dborkman@...hat.com>,
	Jamal Hadi Salim <jhs@...atatu.com>,
	Alexander Duyck <alexander.duyck@...il.com>,
	John Fastabend <john.r.fastabend@...el.com>,
	Toke Høiland-Jørgensen <toke@...e.dk>
Subject: Re: [RFC net-next PATCH V3 0/2] qdisc bulk dequeuing and utilizing
 delayed tailptr updates

On Fri, Sep 19, 2014 at 11:59 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> On Fri, 2014-09-19 at 22:49 +0200, Jesper Dangaard Brouer wrote:
>> This patchset uses DaveM's recent API changes to dev_hard_start_xmit(),
>> from the qdisc layer, to implement dequeue bulking.
>>
>> RFC V3: Keeping the ball rolling.
>>
>> This patchset should now use BQL correctly.  I've done lots of testing
>> for Head-of-Line blocking issues that can occur due to requeue of a
>> SKB bulk list.  I've not been able to provoke any HoL blocking
>> situation, simply because BQL is doing such a good job, thus I'm
>> unable to "overshoot" HW/BQL limits with more than a single packet.
>>
>> This patch chooses a very conservative approach, as by default only
>> allowing dequeue of one extra packet, besides the normal dequeue.
>>
>> Open questions:
>>
>> - How do we expose tuning to userspace?
>>   Patch adds /proc/sys/net/core/qdisc_bulk_dequeue_limit but I don't like it...
>>   Per device tunable?
>>
>
> bql is using /sys, of course ;)
>
> # grep . /sys/class/net/eth1/queues/tx-0/byte_queue_limits/*
> /sys/class/net/eth1/queues/tx-0/byte_queue_limits/hold_time:1000
> /sys/class/net/eth1/queues/tx-0/byte_queue_limits/inflight:0
> /sys/class/net/eth1/queues/tx-0/byte_queue_limits/limit:113314
> /sys/class/net/eth1/queues/tx-0/byte_queue_limits/limit_max:1879048192
> /sys/class/net/eth1/queues/tx-0/byte_queue_limits/limit_min:0
>
> Maybe you could simply reuse byte_queue_limits/limit, I am not sure we
> need a specific tunable.
>
>
>> - Can/should we limit dequeue bulking to devices supporting BQL?
>>
>
> Yes please. This will be an incentive to get BQL on drivers.

While I am +100 on getting more BQL'd drivers out there...

https://www.bufferbloat.net/projects/bloat/wiki/BQL_enabled_drivers

... It was my hope that some of this bulk dequeue work would apply to
wifi packet aggregation one day....

>
>
>



-- 
Dave Täht

https://www.bufferbloat.net/projects/make-wifi-fast
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