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

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Hi!

> I'm debugging strange delays during transmit in stmmac driver. They
> seem to be present in 4.4 kernel (and older kernels, too). Workload is
> burst of udp packets being sent, pause, burst of udp packets, ...
> 
> Test code is attached, I use these parameters for testing:
> 
> ./udp-test raw 10.0.0.6 1234 1000 100 30
> 
> The delays seem to be related to coalescing:
> 
> drivers/net/ethernet/stmicro/stmmac/common.h
> #define STMMAC_COAL_TX_TIMER    40000
> #define STMMAC_MAX_COAL_TX_TICK 100000
> #define STMMAC_TX_MAX_FRAMES    256
> 
> If I lower the parameters, delays are gone, but I get netdev watchdog
> backtrace followed by broken driver.
> 
> Any ideas what is going on there?

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?

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

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stmmac ethernet in kernel 4.4: coalescing related pauses? Pavel Machek <pavel@ucw.cz> - 2016-11-23 12:00 +0100
  stmmac ethernet in kernel 4.9-rc6: coalescing related pauses. Pavel Machek <pavel@ucw.cz> - 2016-11-24 10:00 +0100
    Re: stmmac ethernet in kernel 4.9-rc6: coalescing related pauses. Pavel Machek <pavel@ucw.cz> - 2016-11-24 11:30 +0100
      Re: stmmac ethernet in kernel 4.9-rc6: coalescing related pauses. Pavel Machek <pavel@denx.de> - 2016-11-24 11:40 +0100
        [PATCH] stmmac ethernet: unify locking  Pavel Machek <pavel@ucw.cz> - 2016-11-24 11:50 +0100
          [PATCH] stmmac ethernet: remove cut & paste code Pavel Machek <pavel@ucw.cz> - 2016-11-24 12:10 +0100
            Re: [PATCH] stmmac ethernet: remove cut & paste code Joe Perches <joe@perches.com> - 2016-11-24 21:10 +0100
              Re: [PATCH] stmmac ethernet: remove cut & paste code Pavel Machek <pavel@ucw.cz> - 2016-11-24 23:00 +0100
                Re: [PATCH] stmmac ethernet: remove cut & paste code Joe Perches <joe@perches.com> - 2016-11-24 23:30 +0100
    Re: stmmac ethernet in kernel 4.9-rc6: coalescing related pauses. David Miller <davem@davemloft.net> - 2016-11-24 17:20 +0100
      Re: stmmac ethernet in kernel 4.9-rc6: coalescing related pauses. Pavel Machek <pavel@ucw.cz> - 2016-11-24 22:30 +0100

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