linux-kernel - Re: [PATCH] stmmac: disable tx coalescing

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Date:   Sun, 11 Dec 2016 20:57:48 +0100
From:   Pavel Machek <pavel@....cz>
To:     David Miller <davem@...emloft.net>
Cc:     peppe.cavallaro@...com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, alexandre.torgue@...com,
        LinoSanfilippo@....de
Subject: Re: [PATCH] stmmac: disable tx coalescing

On Sun 2016-12-11 14:31:13, David Miller wrote:
> From: Pavel Machek <pavel@....cz>
> Date: Sun, 11 Dec 2016 20:07:50 +0100
> 
> > David, ping? Can I get you to apply this one?
> > 
> > As you noticed, tx coalescing is completely broken in that driver, and
> > not easy to repair. This is simplest way to disable it. It can still
> > be re-enabled from userspace, so code can be fixed in future.
> 
> Sorry I'm not applying this, I want you and the driver maintainer
> to reach a real solution.

This is what you said about this driver:

# > 4.9-rc6 still has the delays. With the
# >
# > #define STMMAC_COAL_TX_TIMER 1000
# > #define STMMAC_TX_MAX_FRAMES 2
# >
# > settings, delays go away, and driver still works. (It fails fairly
# > fast in 4.4). Good news. But the question still is: what is going on
# > there?
# 
# 256 packets looks way too large for being a trigger for aborting the
# TX coalescing timer.
# 
# Looking more deeply into this, the driver is using non-highres timers
# to implement the TX coalescing.  This simply cannot work.
# 
# 1 HZ, which is the lowest granularity of non-highres timers in the
# kernel, is variable as well as already too large of a delay for
# effective TX coalescing.
# 
# I seriously think that the TX coalescing support should be ripped out
# or disabled entirely until it is implemented properly in this driver.

I'm doing just that -- disabling it entirely until it is done
properly.

Unfortunately, maintainer does not think delays are huge problem. So I
need your help here.

Thanks,									
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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