netdev - Re: [PATCH RFC 2/4] bql: Add tracking of inflight packets

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Message-ID: <20160831112333.5be19dbe@redhat.com>
Date:   Wed, 31 Aug 2016 11:23:33 +0200
From:   Jesper Dangaard Brouer <brouer@...hat.com>
To:     Tom Herbert <tom@...bertland.com>
Cc:     brouer@...hat.com, <davem@...emloft.net>, <netdev@...r.kernel.org>,
        <rick.jones2@....com>, <kernel-team@...com>,
        Achiad Shochat <achiad@...lanox.com>
Subject: Re: [PATCH RFC 2/4] bql: Add tracking of inflight packets

On Tue, 30 Aug 2016 17:00:32 -0700
Tom Herbert <tom@...bertland.com> wrote:

> Add two fields to netdev_queue as head_cnt and tail_cnt. head_cnt is
> incremented for every sent packet in netdev_tx_sent_queue and tail_cnt
> is incremented by the number of packets in netdev_tx_completed_queue.
> So then the number of inflight packets for a queue is simply
> queue->head_cnt - queue->tail_cnt.
> 
> Add inflight_pkts to be reported in sys-fs.

I like the idea of BQL tracking inflight packets, because we could use this
to determine _when_ qdisc bulking could be beneficial (activating xmit_more).

Idea from NetDev1.1 slides[1] page 17, and experiment with BQL
byte_queue_limits/limit_max on page 18 (which would really need a pkt
count not a byte count)

[1] http://people.netfilter.org/hawk/presentations/NetDev1.1_2016/net_performance_BoF.pdf
[2] http://people.netfilter.org/hawk/presentations/NetDev1.1_2016/links.html
-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  Author of http://www.iptv-analyzer.org
  LinkedIn: http://www.linkedin.com/in/brouer