Some more observations with RT_PREEMPT configs enabled.
1) I re-ran the tests disabling all crypto including NEON related
crypto and EFI kernel config options. I still see randomly floating
point register getting corrupted
2) I noticed that, when I run the tests with RT schedulers and RT
priorities, eg: ("chrt -f 5 ./test_float" or "chrt -r 5
./test_float"), I am not able reproduce the corruption issue. But,
when I run the tests (just ./test_float) without any RT scheduler and
priority (i.e SCHED_OTHER) can easily reproduce the issue.
I tried disabling PREEMPT_LAZY, by "echo NO_PREEMPT_LAZY >
/sys/kernel/debug/sched_features". It did not help and am able to
reproduce the problem
3) I have another Cortex ARM A57 system from a different vendor(cannot
name the vendors because of proprietary reasons) with Linux kernel
version 4.9.38 and RT_PREEMPT enabled. I do not see any floating point
corruption issue, even if I run the test as SCHED_OTHER or with real
time settings. So, that tells me moving to 4.18 may not help. What do
you think?
Thanks
Anup
On Sun, Oct 7, 2018 at 9:58 AM Anup Pemmaiah <anup.pemmaiah@xxxxxxxxx> wrote:
>
> > nope, should work by default. Do you have NEON related crypto code or
> > EFI enabled?
>
> Sebastian, Thank you for the comments. I have NEON related crypto code
> enabled right now, but I remember disabling
> it and it did not make a difference. I will disable it again and will
> give it a try. In the mean time, when I disabled the following 4 lines
> from the config file
> and re-compiled the kernel, the test code works fine without the issue
> described earlier related to floating point. Are you suspecting that
> NEON related crypto interferes with real time kernel and not with non-rt kernel?
>
>
> # CONFIG_PREEMPT_RT_BASE=y
>
> # CONFIG_HAVE_PREEMPT_LAZY=y
>
> # CONFIG_PREEMPT_LAZY=y
>
> # CONFIG_PREEMPT_RT_FULL=y
>
>
> > Could you please try the latest v4.18? I believe it is fixed there and
> > needs just backporting. Could you please try?
>
> I will try it as a last resort because I am not sure if the board BSP
> supports v4.18. Right now, I am
> trying to figure out, why it works fine with non-rt kernel and only
> see the issue when the above four RT_PREEMPT config
> options are turned on.
>
>
> On Fri, Oct 5, 2018, 9:55 AM Sebastian Andrzej Siewior
> <sebastian.siewior@xxxxxxxxxxxxx> wrote:
> >
> > On 2018-10-04 19:12:53 [-0700], Anup Pemmaiah wrote:
> > > 1) Is there any floating point related kernel setting that I should
> > > set in the RT_PREEMPT kernel? I have set eagerfpu=on (even though it
> > > is on by default)
> >
> > nope, should work by default. Do you have NEON related crypto code or
> > EFI enabled?
> >
> > > 2) Was reading about "Lazy Stacking" for Cortex-M4, but not sure if it
> > > applies for Cortex A57
> > >
> > > Any comments will be greatly appreciated.
> >
> > Could you please try the latest v4.18? I believe it is fixed there and
> > needs just backporting. Could you please try?
> >
> >
> > Sebastian
>
>
> On Fri, Oct 5, 2018 at 9:55 AM Sebastian Andrzej Siewior
> <sebastian.siewior@xxxxxxxxxxxxx> wrote:
> >
> > On 2018-10-04 19:12:53 [-0700], Anup Pemmaiah wrote:
> > > 1) Is there any floating point related kernel setting that I should
> > > set in the RT_PREEMPT kernel? I have set eagerfpu=on (even though it
> > > is on by default)
> >
> > nope, should work by default. Do you have NEON related crypto code or
> > EFI enabled?
> >
> > > 2) Was reading about "Lazy Stacking" for Cortex-M4, but not sure if it
> > > applies for Cortex A57
> > >
> > > Any comments will be greatly appreciated.
> >
> > Could you please try the latest v4.18? I believe it is fixed there and
> > needs just backporting. Could you please try?
> >
> > Sebastian
