Bisect results for 4.4.1-rt[4,5]

[Tim Sander <tim@krieglstein.org>]

Hi Sebastian

Am Freitag, 12. Februar 2016, 10:07:59 schrieben Sie:
...
> What about rt4? It is only the stable update so you should see here the
> numbers from rt3. If that is true and your numbers are stable it should
> be easy to run git bisect between rt4 and rt5. And looking at
>   https://git.kernel.org/rt/linux-rt-devel/h/v4.4.1-rt5
> the only non-cosmetic change in -rt5 that should affect you is the
> migrate-disable fixup from Mike.
I have done a bisect run, its a rather innocent looking on liner which seems 
to cause the problems. The numbers where reasonably stable so i am pretty 
confident that this is the patch giving ~26µs additional latency on the Altera
SOC plattform:

eec2bf477ac674583a7d73b9d00f47c528b7266d is the first bad commit
commit eec2bf477ac674583a7d73b9d00f47c528b7266d
Author: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date:   Thu Feb 4 16:38:10 2016 +0100

    kernel/perf: mark perf_cpu_context's timer as irqsafe
    
    Otherwise we get a WARN_ON() backtrace and some events are reported as
    "not counted".
    
    Cc: stable-rt@vger.kernel.org
    Reported-by: Yang Shi <yang.shi@linaro.org>
    Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

Here are the numbers of the bisect run for reference:
==> g0dd3bdd <==
# Total: 100000000 099999829
# Min Latencies: 00010 00010
# Avg Latencies: 00020 00021
# Max Latencies: 00084 00101
# Histogram Overflows: 00000 00000

==> gbbc7819 <==
# Total: 100000000 099999798
# Min Latencies: 00010 00010
# Avg Latencies: 00021 00021
# Max Latencies: 00086 00091
# Histogram Overflows: 00000 00000

==> geec2bf4 <==
# Total: 099998713 100000000
# Min Latencies: 00010 00010
# Avg Latencies: 00020 00021
# Max Latencies: 00113 00070
# Histogram Overflows: 00000 00000

Best Regards
Tim