netdev - Re: [PATCH net] net: stmmac: Use hrtimer for TX coalescing

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Date:   Mon, 23 Nov 2020 16:46:00 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Vincent Whitchurch <vincent.whitchurch@...s.com>
Cc:     <peppe.cavallaro@...com>, <alexandre.torgue@...com>,
        <joabreu@...opsys.com>, <davem@...emloft.net>, <kernel@...s.com>,
        <netdev@...r.kernel.org>
Subject: Re: [PATCH net] net: stmmac: Use hrtimer for TX coalescing

On Fri, 20 Nov 2020 16:02:08 +0100 Vincent Whitchurch wrote:
> This driver uses a normal timer for TX coalescing, which means that the
> with the default tx-usecs of 1000 microseconds the cleanups actually
> happen 10 ms or more later with HZ=100.  This leads to very low
> througput with TCP when bridged to a slow link such as a 4G modem.  Fix
> this by using an hrtimer instead.
> 
> On my ARM platform with HZ=100 and the default TX coalescing settings
> (tx-frames 25 tx-usecs 1000), with "tc qdisc add dev eth0 root netem
> delay 60ms 40ms rate 50Mbit" run on the server, netperf's TCP_STREAM
> improves from ~5.5 Mbps to ~100 Mbps.
> 
> Signed-off-by: Vincent Whitchurch <vincent.whitchurch@...s.com>

Looks perfectly reasonable, but you marked it for net. Do you consider
this to be a bug fix, and need it backported to stable? Otherwise I'd
rather apply it to net-next.