[PATCH] arch/arm64 :Cyclic Test fix in ARM64 fpsimd

[tglx@linutronix.de (Thomas Gleixner)]

On Mon, 18 May 2015, Sebastian Andrzej Siewior wrote:

> * Gary Robertson | 2015-05-18 08:23:16 [-0500]:
> 
> >I have been following this thread and was able to obtain a copy of the full
> >log from Anders.
> >My initial impression based upon the log entries is that the excessive
> >latencies did not occur during the fpsimd calls -
> >but the actual progress of an individual task is a bit difficult to follow
> >through the logs, so in my spare time
> >I started writing a parser to sort it into a format easier to follow.  I
> >hope to have it completed shortly.
> >This parser will sort the log first by CPU and then by thread so the cause
> >of the delay will be easier to see.
> 
> There is a smaller version of it at 
>     https://breakpoint.cc/arm64_simd_trace_cpu.txt
> 
> which contains only CPU0 around that "event. Here are a few pieces:
> |cyclicte-964     0....1.. 511965877us : __schedule <-schedule
> cyclictest goes away
> 
> |kworker/-353     0....111 511965906us : rt_spin_unlock <-process_one_work
> kworker is now active
> 
> |kworker/-353     0....112 511965954us : kernel_neon_begin_partial <-virt_efi_set_time
> |kworker/-353     0....112 511965955us : preempt_count_add <-kernel_neon_begin_partial
> and kworker invokes virt_efi_set_time which does the neon save thingy.
> 
> |kworker/-353     0d...212 511966764us : __handle_domain_irq <-gic_handle_irq
> now we have an interrupt comming.
> 
> |kworker/-353     0dn.h412 511966793us : task_woken_rt <-ttwu_do_wakeup
> it might be the timer for cyclictest wakeup it might not, however we
> have the N flag set and kworker has to go.
> 
> |kworker/-353     0dn..212 511966806us : rcu_sysidle_enter <-rcu_irq_exit
> |kworker/-353     0dn..212 511967108us : __handle_domain_irq <-gic_handle_irq
> |kworker/-353     0dn..212 511967109us : irq_enter <-__handle_domain_irq
> so we finished handling one irq and we contiunue with the next one? This
> goes on and on and on until finally after a while we have this:
> 
> |kworker/-353     0dn..212 512064373us : rcu_irq_exit <-irq_exit
> |kworker/-353     0dn..212 512064374us : rcu_sysidle_enter <-rcu_irq_exit
> |kworker/-353     0.n..212 512065116us : kernel_neon_end <-virt_efi_set_time
> |kworker/-353     0.n..212 512065116us : preempt_count_sub <-kernel_neon_end
> |kworker/-353     0.n..112 512065117us : __schedule <-preempt_schedule
> 
> and this time we were able to return from rcu_irq_exit and continue with
> virt_efi_set_time and finally switch the task. So yes, preemption was
> disabled during kernel_neon_{being|end} but we also received 81
> interrupt ("gic_handle_irq invocation") during that time. Why is that?

> |kworker/-353     0dn..212 512064373us : rcu_irq_exit <-irq_exit
> |kworker/-353     0dn..212 512064374us : rcu_sysidle_enter <-rcu_irq_exit

That's called from RCU_NONIDLE(). Go figure ...

Thanks,

	tglx