Hello ,
I have gone through below code and i felt logic is different with
respect to arm code . please find my findings.
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -347,11 +347,16 @@ el1_irq:
#ifdef CONFIG_PREEMPT
get_thread_info tsk
ldr w24, [tsk, #TI_PREEMPT] // get preempt count
- cbnz w24, 1f // preempt count != 0
+ cbnz w24, 2f // preempt count != 0
ldr x0, [tsk, #TI_FLAGS] // get flags
- tbz x0, #TIF_NEED_RESCHED, 1f // needs rescheduling?
- bl el1_preempt
+ tbz x0, #_TIF_NEED_RESCHED, 2f // needs rescheduling?
+
+ ldr w24, [tsk, #TI_PREEMPT_LAZY] // get preempt lazy count
+ cbnz w24, 1f // preempt count != 0
+ tbz x0, #_TIF_NEED_RESCHED_LAZY, 2f // needs rescheduling?
1:
+ bl el1_preempt
+2:
#endif
My findings:
-----------------
1) + tbz x0, #_TIF_NEED_RESCHED, 2f // needs rescheduling?
=> Here we should proceed to check TI_PREEMPT_LAZY conditions if
_TIF_NEED_RESCHED is not set. . If it is set, it should jump to
el1_preempt.
2) fast_work_pending handler also should check TI_PREEMPT_LAZY flags
as per defined in arm.
Thanks and regards,
Ayyappa.Ch
On Mon, Apr 13, 2015 at 7:32 PM, Sebastian Andrzej Siewior
<bigeasy@xxxxxxxxxxxxx> 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? 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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