[S390] s390: Optimize user and work TIF check

On return from syscall or interrupt, we have to check if we return to
userspace (likely) and if there is work todo (less likely) to decide
if we handle the work. We can optimize this check: we first check for
the less likely work case and then check for userspace.

This patch is also a preparation for an additional patch, that fixes a bug
in KVM dealing with cpu bound guests.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

1 files changed, 14 insertions, 15 deletions

diff --git a/arch/s390/kernel/entry64.S b/arch/s390/kernel/entry64.S
index 5a4a7bcd2bba..a57909d63149 100644
--- a/arch/s390/kernel/entry64.S
+++ b/arch/s390/kernel/entry64.S
@@ -271,8 +271,6 @@ sysc_noemu:
         stg     %r2,SP_R2(%r15) # store return value (change R2 on stack)
 
 sysc_return:
-        tm      SP_PSW+1(%r15),0x01     # returning to user ?
-        jno     sysc_restore
         tm      __TI_flags+7(%r9),_TIF_WORK_SVC
         jnz     sysc_work       # there is work to do (signals etc.)
 sysc_restore:
@@ -304,6 +302,8 @@ sysc_work_loop:
 # One of the work bits is on. Find out which one.
 #
 sysc_work:
+        tm      SP_PSW+1(%r15),0x01     # returning to user ?
+        jno     sysc_restore
         tm      __TI_flags+7(%r9),_TIF_MCCK_PENDING
         jo      sysc_mcck_pending
         tm      __TI_flags+7(%r9),_TIF_NEED_RESCHED
@@ -585,12 +585,6 @@ io_no_vtime:
         la      %r2,SP_PTREGS(%r15)     # address of register-save area
         brasl   %r14,do_IRQ             # call standard irq handler
 io_return:
-        tm      SP_PSW+1(%r15),0x01     # returning to user ?
-#ifdef CONFIG_PREEMPT
-        jno     io_preempt              # no -> check for preemptive scheduling
-#else
-        jno     io_restore              # no-> skip resched & signal
-#endif
         tm      __TI_flags+7(%r9),_TIF_WORK_INT
         jnz     io_work                 # there is work to do (signals etc.)
 io_restore:
@@ -612,10 +606,18 @@ io_restore_trace_psw:
         .quad   0, io_restore_trace
 #endif
 
-#ifdef CONFIG_PREEMPT
-io_preempt:
+#
+# switch to kernel stack, then check TIF bits
+#
+io_work:
+        tm      SP_PSW+1(%r15),0x01     # returning to user ?
+#ifndef CONFIG_PREEMPT
+        jno     io_restore              # no-> skip resched & signal
+#else
+        jnz     io_work_user            # yes -> do resched & signal
+        # check for preemptive scheduling
         icm     %r0,15,__TI_precount(%r9)
-        jnz     io_restore
+        jnz     io_restore              # preemption is disabled
         # switch to kernel stack
         lg      %r1,SP_R15(%r15)
         aghi    %r1,-SP_SIZE
@@ -629,10 +631,7 @@ io_resume_loop:
         jg      preempt_schedule_irq
 #endif
 
-#
-# switch to kernel stack, then check TIF bits
-#
-io_work:
+io_work_user:
         lg      %r1,__LC_KERNEL_STACK
         aghi    %r1,-SP_SIZE
         mvc     SP_PTREGS(__PT_SIZE,%r1),SP_PTREGS(%r15)