From: Willy Tarreau <w@1wt•eu>
To: Marcin Wojtas <mw@semihalf•com>
Cc: thomas.petazzoni@free-electrons•com, andrew@lunn•ch,
linux@arm•linux.org.uk, jason@lakedaemon•net,
netdev@vger•kernel.org, linux-kernel@vger•kernel.org,
stable@vger•kernel.org, Dmitri Epshtein <dima@marvell•com>,
nadavh@marvell•com, alior@marvell•com, jaz@semihalf•com,
gregory.clement@free-electrons•com, nitroshift@yahoo•com,
davem@davemloft•net, linux-arm-kernel@lists•infradead.org,
sebastian.hesselbarth@gmail•com
Subject: Re: [PATCH net] net: mvneta: set real interrupt per packet for tx_done
Date: Wed, 6 Jul 2016 07:04:31 +0200 [thread overview]
Message-ID: <20160706050431.GA26348@1wt.eu> (raw)
In-Reply-To: <1467771538-31811-1-git-send-email-mw@semihalf.com>
Hi,
On Wed, Jul 06, 2016 at 04:18:58AM +0200, Marcin Wojtas wrote:
> From: Dmitri Epshtein <dima@marvell•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.
We had a discussion about this in January 2015 and I thought I sent a patch
to change it but I can't find it, so I think it was only proposed to some
users for testing. I also remember that on more recent kernels by then
(>=3.13) we observed a slightly better performance with this value set to
zero.
Acked-by: Willy Tarreau <w@1wt•eu>
Willy
next prev parent reply other threads:[~2016-07-06 5:04 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-07-06 2:18 [PATCH net] net: mvneta: set real interrupt per packet for tx_done Marcin Wojtas
2016-07-06 5:04 ` Willy Tarreau [this message]
2016-07-09 3:45 ` David Miller
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