Re: Regression: Failed boots bisected to 4cd13c21b207 "softirq: Let ksoftirqd do its job"

[Brian Starkey]

Hi Eric,

On Tue, Nov 22, 2016 at 06:29:33AM -0800, Eric Dumazet wrote:
> On Tue, Nov 22, 2016 at 2:33 AM, Brian Starkey <brian.starkey@xxxxxxx> wrote:
> > Hi,
> >
> > On Fri, Nov 18, 2016 at 01:40:43AM +0100, Thomas Gleixner wrote:
> > > Brian,
> > >
> > > On Thu, 17 Nov 2016, Brian Starkey wrote:
> > > > No joy with this patch :-(
> > > >
> > > > I had to add an ioaddr argument because apparently that macro depends
> > > > on local context (yuck...), but it doesn't help my issue.
> > > >
> > > > FWIW I don't see any timeouts, either with or without the patch.
> > > > (I don't know for sure, but I would guess that the model of the
> > > > network card doesn't model whatever stall that loop is checking for.
> > > > It probably just completes all MMU operations immediately)
> > >
> > >
> > > Is there a chance that you enable trace points at the kernel command line?
> > >
> > >  trace_event=sched_wakeup,sched_switch,irq_handler_entry,irq_handler_exit,softirq_raise,softirq_entry,softirq_exit
> > >
> > > should be enough for a start. All we need aside of that is a trigger to
> > > stop the trace so we can actually see the events around the time where
> > > things go stale.
> > >
> > > I assume that the whole issue is visible throughout the slow progress of
> > > init towards a working system, so for a start it would be sufficient to add
> > > something like this into the startup sequence at some point:
> > >
> > > mount -t debugfs debugfs /sys/kernel/debug
> > > echo 0 >/sys/kernel/debug/tracing/tracing_on
> > >
> > > The only interesting challange is to get the trace data out of the
> > > system. The trace is accessible via:
> > >
> > > cat /sys/kernel/tracing/trace
> > >
> > > So if your ssh works at some point, that might be an option or you just try
> > > to store it over NFS (which will be slow, but better than nothing). Maybe
> > > you have a better idea :)
> >
> >
> > I finally managed to pry some traces out this morning. It seems like
> > the system struggles to even invoke echo when it's doing badly.
> >
> > Trace before 4cd13c21b207: https://drive.google.com/open?id=0B8siaK6ZjvEwU21wNTdZS29kVXc
> > Trace after 4cd13c21b207: https://drive.google.com/open?id=0B8siaK6ZjvEwbXVzcnpieVkzWFU
> > (btw, if there's a preferred way to send the logs let me know. I
> > wasn't sure large or non-text attachments would be well received)
> >
> > I'm not sure how much help the trace is, but it does look like the
> > system is spending far too much time in the ethernet device's IRQ
> > handler to be healthy.
>
> Thanks a lot Brian
>
> Can you confirm interrupt handler is smc911x_interrupt() ?
>
> (ie : is SMC_USE_PXA_DMA / SMC_USE_DMA defined or not ?)

Looks like there's a few similarly named devices and drivers. Mine is
an SMSC LAN91C111 using the smc91x driver in
drivers/net/ethernet/smsc/smc91x.c, rather than smc911x.c. So the
interrupt handler is smc_interrupt()

CONFIG_ARCH_PXA is not set, nor is SMC_USE_PXA_DMA or SMC_USE_DMA.

-Brian

> > Thanks,
> > Brian
> > > Thanks,
> > >
> > >         tglx