netdev - Re: Strange tg3 regression with UMP fw. link reporting

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Date:	Fri, 8 Aug 2008 16:25:58 -0500
From:	Nathan Lynch <ntl@...ox.com>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc:	Segher Boessenkool <segher@...nel.crashing.org>,
	mcarlson@...adcom.com, linuxppc-dev list <linuxppc-dev@...abs.org>,
	netdev <netdev@...r.kernel.org>,
	Michael Chan <mchan@...adcom.com>
Subject: Re: Strange tg3 regression with UMP fw. link reporting

Benjamin Herrenschmidt wrote:
> On Fri, 2008-08-08 at 10:58 +0200, Segher Boessenkool wrote:
> > > I don't know yet for sure what happens, but a quick look at the commit
> > > seems to show that the driver synchronously spin-waits for up to 2.5ms
> > 
> > That's what the comment says, but the code says 2.5 _seconds_:
> > 
> > +       /* Wait for up to 2.5 milliseconds */
> > +       for (i = 0; i < 250000; i++) {
> > +               if (!(tr32(GRC_RX_CPU_EVENT) & GRC_RX_CPU_DRIVER_EVENT))
> > +                       break;
> > +               udelay(10);
> > +       }
> > 
> > (not that milliseconds wouldn't be bad already...)
> 
> Right, indeed. I think we have a good candidate for the problem :-)

I put a printk in tg3_wait_for_event_ack and I can confirm that it's
timing out frequently (every few seconds) on my system.  Changing the
number of loop iterations to 250 alleviates the problem.
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