Re: stmmac ethernet in kernel 4.9-rc6: coalescing related pauses.

Hi!

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We had experimented this tuning on STB IP where just datagrams
had to send externally. To be honest, although we had seen
better results w/o any timer, we kept this approach enabled
because the timer was fast enough to cover our tests on SH4 boxes.

Please reply to David, and explain how it is supposed to
work... because right now it does not. 40 msec delays are not
acceptable in default configuration.

I mean, that on UP and SMP system this schema helped
to improve the performance saving CPU on my side and this has been
tested since a long time (~4 years).
I tested something similar to yours where unidirectional traffic
with limited throughput was needed and I can confirm you that
tuning/removing coalesce parameters this helped. The tuning I decided
to keep in the driver was suitable in several user cases and if now
you have problems or you want to review it I can just confirm that
there are no problems on my side. If you want to simply the logic
around the tx process and remove timer on official driver I can accept
that. I will just ask you uto double check if the throughput and
CPU usage when request max throughput (better if on GiGa setup) has
no regressions.
Otherwise we could start thinking about adaptive schema if feasible.

Ok, so you see the issue. Good.

See the other email to description how it could be fixed... the logic
is broken. How it was not discovered for 4 years is mystery to me.
 

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Agreed that no irqlock protection is needed if we rely on napi and timers.

ok

Actually I was wrong there. Another reason to disable tx coalescing
until it is fixed.

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