* 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? Out of curiosity, how likely is it
that I can login on one of these machines if I send you a ssh key?
> 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 :)
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?
Sebastian
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