linux-kernel - Re: [PATCH net] net: mvneta: set real interrupt per packet for tx

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Message-Id: <20160708.234518.1265002080156810187.davem@davemloft.net>
Date:	Fri, 08 Jul 2016 23:45:18 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	mw@...ihalf.com
Cc:	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	netdev@...r.kernel.org, linux@....linux.org.uk,
	sebastian.hesselbarth@...il.com, andrew@...n.ch,
	jason@...edaemon.net, thomas.petazzoni@...e-electrons.com,
	gregory.clement@...e-electrons.com, nadavh@...vell.com,
	alior@...vell.com, nitroshift@...oo.com, jaz@...ihalf.com,
	dima@...vell.com, stable@...r.kernel.org
Subject: Re: [PATCH net] net: mvneta: set real interrupt per packet for
 tx_done

From: Marcin Wojtas <mw@...ihalf.com>
Date: Wed,  6 Jul 2016 04:18:58 +0200

> From: Dmitri Epshtein <dima@...vell.com>
> 
> Commit aebea2ba0f74 ("net: mvneta: fix Tx interrupt delay") intended to
> set coalescing threshold to a value guaranteeing interrupt generation
> per each sent packet, so that buffers can be released with no delay.
> 
> In fact setting threshold to '1' was wrong, because it causes interrupt
> every two packets. According to the documentation a reason behind it is
> following - interrupt occurs once sent buffers counter reaches a value,
> which is higher than one specified in MVNETA_TXQ_SIZE_REG(q). This
> behavior was confirmed during tests. Also when testing the SoC working
> as a NAS device, better performance was observed with int-per-packet,
> as it strongly depends on the fact that all transmitted packets are
> released immediately.
> 
> This commit enables NETA controller work in interrupt per sent packet mode
> by setting coalescing threshold to 0.
> 
> Signed-off-by: Dmitri Epshtein <dima@...vell.com>
> Signed-off-by: Marcin Wojtas <mw@...ihalf.com>
> Cc: <stable@...r.kernel.org> # v3.10+
> Fixes aebea2ba0f74 ("net: mvneta: fix Tx interrupt delay")

Applied, thanks.