On 2015-04-13 16:02, Sebastian Andrzej Siewior wrote:
> * Anders Roxell | 2015-04-12 09:59:38 [+0200]:
>
> >arm64 is missing support for PREEMPT_RT. The main feature which is
> >lacking is support for lazy preemption. The arch-specific entry code,
> >thread information structure definitions, and associated data tables
> >have to be extended to provide this support. Then the Kconfig file has
> >to be extended to indicate the support is available, and also to
> >indicate that support for full RT preemption is now available.
> >
> >Signed-off-by: Anders Roxell <anders.roxell@xxxxxxxxxx>
> >---
> >
> >I tested this on an arm64 juno target, to get that to boot I had to
> >backport the dtb from v4.0-rc6 to v3.18.11-rt6.
>
> Seriously? It all works by itself?
I would say yes, but now you get me wondering... =)
> Out of curiosity, how likely is it
> that I can login on one of these machines if I send you a ssh key?
I will look into that.
>
> > arch/arm64/Kconfig | 2 ++
> > arch/arm64/include/asm/thread_info.h | 3 +++
> > arch/arm64/kernel/asm-offsets.c | 1 +
> > arch/arm64/kernel/entry.S | 14 ++++++++++----
> > 4 files changed, 16 insertions(+), 4 deletions(-)
> >
> >diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> >index 9532f8d..62f4e00 100644
> >--- a/arch/arm64/Kconfig
> >+++ b/arch/arm64/Kconfig
> >@@ -59,7 +59,9 @@ config ARM64
> > select HAVE_PERF_REGS
> > select HAVE_PERF_USER_STACK_DUMP
> > select HAVE_RCU_TABLE_FREE
> >+ select HAVE_PREEMPT_LAZY
> > select HAVE_SYSCALL_TRACEPOINTS
> >+ select IRQ_FORCED_THREADING
>
> Did you mark all non-threadable interrupts? Commit da0ec6f7c1e ("ARM:
> 7814/2: Allow forced irq threading") was the patch for ARM. If so you
> could take this piece and send upstream and get the kernel commandline
> "threadirqs" working without -RT :)
I will try to do that.
>
> For the lazy-preempt pieces, arch/arm64/kernel/entry.S, work_pending
> checks only for TIF_NEED_RESCHED while arm checks for both (this and
> _TIF_NEED_RESCHED_LAZY). You sure you don't need it?
I'm have my doubts now, I have to investigate that.
>
> Sebastian
Cheers,
Anders
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