netdev - Re: [PATCH] net: mvneta: fix handling of the Tx descriptor counter

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Message-ID: <20171113153614.GN18407@kw.sim.vm.gnt>
Date:   Mon, 13 Nov 2017 16:36:14 +0100
From:   Simon Guinot <simon.guinot@...uanux.org>
To:     David Miller <davem@...emloft.net>
Cc:     thomas.petazzoni@...e-electrons.com, netdev@...r.kernel.org,
        musv@....de, andreas.tobler@...udguard.ch,
        gregory.clement@...e-electrons.com,
        antoine.tenart@...e-electrons.com, mw@...ihalf.com,
        stable@...r.kernel.org
Subject: Re: [PATCH] net: mvneta: fix handling of the Tx descriptor counter

On Mon, Nov 13, 2017 at 11:54:14PM +0900, David Miller wrote:
> From: Simon Guinot <simon.guinot@...uanux.org>
> Date: Mon, 13 Nov 2017 15:51:15 +0100
> 
> > IIUC the driver stops the queue if a threshold of 316 Tx descriptors is
> > reached (default and worst value).
> 
> That's a lot of latency.

OK, then I'll keep the "tx_pending > 255" flushing condition. But note
there is no other software mechanism to limit the Tx latency inside the
mvneta driver. Should we add something ? And is that not rather the job
of the network stack to keep track of the latency and to limit the txq
size ?

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