[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/entry.S b/arch/s390/kernel/entry.S
index bdbb3bcd78a5..708cf9cf9a35 100644
--- a/arch/s390/kernel/entry.S
+++ b/arch/s390/kernel/entry.S
@@ -279,8 +279,6 @@ sysc_do_restart:
         st      %r2,SP_R2(%r15)   # store return value (change R2 on stack)
 
 sysc_return:
-        tm      SP_PSW+1(%r15),0x01     # returning to user ?
-        bno     BASED(sysc_restore)
         tm      __TI_flags+3(%r9),_TIF_WORK_SVC
         bnz     BASED(sysc_work)  # there is work to do (signals etc.)
 sysc_restore:
@@ -312,6 +310,8 @@ 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 ?
+        bno     BASED(sysc_restore)
         tm      __TI_flags+3(%r9),_TIF_MCCK_PENDING
         bo      BASED(sysc_mcck_pending)
         tm      __TI_flags+3(%r9),_TIF_NEED_RESCHED
@@ -602,12 +602,6 @@ io_no_vtime:
         la      %r2,SP_PTREGS(%r15)     # address of register-save area
         basr    %r14,%r1                # branch to standard irq handler
 io_return:
-        tm      SP_PSW+1(%r15),0x01     # returning to user ?
-#ifdef CONFIG_PREEMPT
-        bno     BASED(io_preempt)       # no -> check for preemptive scheduling
-#else
-        bno     BASED(io_restore)       # no-> skip resched & signal
-#endif
         tm      __TI_flags+3(%r9),_TIF_WORK_INT
         bnz     BASED(io_work)          # there is work to do (signals etc.)
 io_restore:
@@ -629,10 +623,18 @@ io_restore_trace_psw:
         .long   0, io_restore_trace + 0x80000000
 #endif
 
-#ifdef CONFIG_PREEMPT
-io_preempt:
+#
+# switch to kernel stack, then check the TIF bits
+#
+io_work:
+        tm      SP_PSW+1(%r15),0x01     # returning to user ?
+#ifndef CONFIG_PREEMPT
+        bno     BASED(io_restore)       # no-> skip resched & signal
+#else
+        bnz     BASED(io_work_user)     # no -> check for preemptive scheduling
+        # check for preemptive scheduling
         icm     %r0,15,__TI_precount(%r9)
-        bnz     BASED(io_restore)
+        bnz     BASED(io_restore)       # preemption disabled
         l       %r1,SP_R15(%r15)
         s       %r1,BASED(.Lc_spsize)
         mvc     SP_PTREGS(__PT_SIZE,%r1),SP_PTREGS(%r15)
@@ -646,10 +648,7 @@ io_resume_loop:
         br      %r1                     # call schedule
 #endif
 
-#
-# switch to kernel stack, then check the TIF bits
-#
-io_work:
+io_work_user:
         l       %r1,__LC_KERNEL_STACK
         s       %r1,BASED(.Lc_spsize)
         mvc     SP_PTREGS(__PT_SIZE,%r1),SP_PTREGS(%r15)