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ARC: [arcompact] entry.S: Elide extra check/branch in exception ret path 

This is done by improving the laddering logic !

Before:

   if Exception
      goto excep_or_pure_k_ret

   if !Interrupt(L2)
      goto l1_chk
   else
      INTERRUPT_EPILOGUE 2

 l1_chk:
   if !Interrupt(L1)  (i.e. pure kernel mode)
      goto excep_or_pure_k_ret
   else
      INTERRUPT_EPILOGUE 1

 excep_or_pure_k_ret:
   EXCEPTION_EPILOGUE

Now:

   if !Interrupt(L1 or L2) (i.e. exception or pure kernel mode)
      goto excep_or_pure_k_ret

  ; guaranteed to be an interrupt
   if !Interrupt(L2)
      goto l1_ret
   else
      INTERRUPT_EPILOGUE 2

 ; by virtue of above, no need to chk for L1 active
 l1_ret:
    INTERRUPT_EPILOGUE 1

 excep_or_pure_k_ret:
    EXCEPTION_EPILOGUE

Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
hifive-unleashed-5.1
Vineet Gupta 2015-10-08 17:52:27 +05:30
parent 5f88808745
commit 9fabcc636b
1 changed files with 6 additions and 12 deletions
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18
arch/arc/kernel/entry-compact.S
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@ -333,11 +333,10 @@ END(call_do_page_fault)
; Note that we use realtime STATUS32 (not pt_regs->status32) to
; decide that.
; if Returning from Exception
btst r10, STATUS_AE_BIT
bnz .Lexcep_ret
and.f 0, r10, (STATUS_A1_MASK|STATUS_A2_MASK)
bz .Lexcep_or_pure_K_ret
; Not Exception so maybe Interrupts (Level 1 or 2)
; Returning from Interrupts (Level 1 or 2)
#ifdef CONFIG_ARC_COMPACT_IRQ_LEVELS
@ -378,8 +377,7 @@ END(call_do_page_fault)
st r9, [r10, THREAD_INFO_PREEMPT_COUNT]
149:
;return from level 2
INTERRUPT_EPILOGUE 2
INTERRUPT_EPILOGUE 2 ; return from level 2 interrupt
debug_marker_l2:
rtie
@ -387,15 +385,11 @@ not_level2_interrupt:
#endif
bbit0 r10, STATUS_A1_BIT, .Lpure_k_mode_ret
;return from level 1
INTERRUPT_EPILOGUE 1
INTERRUPT_EPILOGUE 1 ; return from level 1 interrupt
debug_marker_l1:
rtie
.Lexcep_ret:
.Lpure_k_mode_ret:
.Lexcep_or_pure_K_ret:
;this case is for syscalls or Exceptions or pure kernel mode