Re: [PATCH] stmmac: disable tx coalescing

On Sun 2016-12-11 14:31:13, David Miller wrote:

From: Pavel Machek <redacted>
Date: Sun, 11 Dec 2016 20:07:50 +0100

quoted

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