[IA64] Reschedule fsys_bubble_down().

Improvements come from eliminating srlz.i, not scheduling AR/CR-reads
too early (while there are others still pending), scheduling the
backing-store switch as well as possible, splitting the BBB bundle
into a MIB/MBB pair.

Why is it safe to eliminate the srlz.i?  Observe
that we used to clear bits ~PSR_PRESERVED_BITS in PSR.L.  Since
PSR_PRESERVED_BITS==PSR.{UP,MFL,MFH,PK,DT,PP,SP,RT,IC}, we
ended up clearing PSR.{BE,AC,I,DFL,DFH,DI,DB,SI,TB}.  However,

 PSR.BE : already is turned off in __kernel_syscall_via_epc()
 PSR.AC : don't care (kernel normally turns PSR.AC on)
 PSR.I  : already turned off by the time fsys_bubble_down gets invoked
 PSR.DFL: always 0 (kernel never turns it on)
 PSR.DFH: don't care --- kernel never touches f32-f127 on its own
	  initiative
 PSR.DI : always 0 (kernel never turns it on)
 PSR.SI : always 0 (kernel never turns it on)
 PSR.DB : don't care --- kernel never enables kernel-level breakpoints
 PSR.TB : must be 0 already; if it wasn't zero on entry to
	  __kernel_syscall_via_epc, the branch to fsys_bubble_down
	  will trigger a taken branch; the taken-trap-handler then
	  converts the syscall into a break-based system-call.

In other words: all the bits we're clearying are either 0 already or
are don't cares!  Thus, we don't have to write PSR.L at all and we
don't have to do a srlz.i either.

Good for another ~20 cycle improvement for EPC-based heavy-weight
syscalls.

Signed-off-by: David Mosberger-Tang <davidm@hpl.hp.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>

1 files changed, 33 insertions, 40 deletions

diff --git a/arch/ia64/kernel/fsys.S b/arch/ia64/kernel/fsys.S
index 0d8650f7fce7..57c6556b1e06 100644
--- a/arch/ia64/kernel/fsys.S
+++ b/arch/ia64/kernel/fsys.S
@@ -549,9 +549,6 @@ GLOBAL_ENTRY(fsys_bubble_down)
          *      - r27: ar.rsc
          *      - r29: psr
          */
-#       define PSR_PRESERVED_BITS       (IA64_PSR_UP | IA64_PSR_MFL | IA64_PSR_MFH | IA64_PSR_PK \
-                                         | IA64_PSR_DT | IA64_PSR_PP | IA64_PSR_SP | IA64_PSR_RT \
-                                         | IA64_PSR_IC)
         /*
          * Reading psr.l gives us only bits 0-31, psr.it, and psr.mc.  The rest we have
          * to synthesize.
@@ -560,62 +557,58 @@ GLOBAL_ENTRY(fsys_bubble_down)
                                          | IA64_PSR_BN | IA64_PSR_I)
 
         invala
-        movl r8=PSR_ONE_BITS
+        movl r14=ia64_ret_from_syscall
 
-        mov r25=ar.unat                 // save ar.unat (5 cyc)
-        movl r9=PSR_PRESERVED_BITS
-
-        mov ar.rsc=0                    // set enforced lazy mode, pl 0, little-endian, loadrs=0
+        nop.m 0
         movl r28=__kernel_syscall_via_break
         ;;
-        mov r23=ar.bspstore             // save ar.bspstore (12 cyc)
-        mov r31=pr                      // save pr (2 cyc)
-        mov r20=r1                      // save caller's gp in r20
-        ;;
+
         mov r2=r16                      // copy current task addr to addl-addressable register
-        and r9=r9,r29
-        mov r19=b6                      // save b6 (2 cyc)
+        adds r16=IA64_TASK_THREAD_ON_USTACK_OFFSET,r16
+        mov r31=pr                      // save pr (2 cyc)
         ;;
-        mov psr.l=r9                    // slam the door (17 cyc to srlz.i)
-        or r29=r8,r29                   // construct cr.ipsr value to save
+        st1 [r16]=r0                    // clear current->thread.on_ustack flag
         addl r22=IA64_RBS_OFFSET,r2     // compute base of RBS
+        add r3=TI_FLAGS+IA64_TASK_SIZE,r2
         ;;
-        // GAS reports a spurious RAW hazard on the read of ar.rnat because it thinks
-        // we may be reading ar.itc after writing to psr.l.  Avoid that message with
-        // this directive:
-        dv_serialize_data
-        mov.m r24=ar.rnat               // read ar.rnat (5 cyc lat)
+        ld4 r3=[r3]                             // r2 = current_thread_info()->flags
         lfetch.fault.excl.nt1 [r22]
-        adds r16=IA64_TASK_THREAD_ON_USTACK_OFFSET,r2
-
-        // ensure previous insn group is issued before we stall for srlz.i:
+        nop.i 0
         ;;
-        srlz.i                          // ensure new psr.l has been established
-        /////////////////////////////////////////////////////////////////////////////
-        ////////// from this point on, execution is not interruptible anymore
-        /////////////////////////////////////////////////////////////////////////////
-        addl r1=IA64_STK_OFFSET-IA64_PT_REGS_SIZE,r2    // compute base of memory stack
-        cmp.ne pKStk,pUStk=r0,r0        // set pKStk <- 0, pUStk <- 1
+        mov ar.rsc=0                    // set enforced lazy mode, pl 0, little-endian, loadrs=0
+        nop.m 0
+        nop.i 0
+        ;;
+        mov r23=ar.bspstore             // save ar.bspstore (12 cyc)
+        mov.m r24=ar.rnat               // read ar.rnat (5 cyc lat)
+        nop.i 0
         ;;
-        st1 [r16]=r0                    // clear current->thread.on_ustack flag
         mov ar.bspstore=r22             // switch to kernel RBS
-        mov b6=r18                      // copy syscall entry-point to b6 (7 cyc)
-        add r3=TI_FLAGS+IA64_TASK_SIZE,r2
+        movl r8=PSR_ONE_BITS                    // X
         ;;
-        ld4 r3=[r3]                             // r2 = current_thread_info()->flags
+        mov r25=ar.unat                 // save ar.unat (5 cyc)
+        mov r19=b6                      // save b6 (2 cyc)
+        mov r20=r1                      // save caller's gp in r20
+        ;;
+        or r29=r8,r29                   // construct cr.ipsr value to save
+        mov b6=r18                      // copy syscall entry-point to b6 (7 cyc)
+        addl r1=IA64_STK_OFFSET-IA64_PT_REGS_SIZE,r2    // compute base of memory stack
+
         mov r18=ar.bsp                  // save (kernel) ar.bsp (12 cyc)
-        mov ar.rsc=0x3                  // set eager mode, pl 0, little-endian, loadrs=0
+        cmp.ne pKStk,pUStk=r0,r0        // set pKStk <- 0, pUStk <- 1
         br.call.sptk.many b7=ia64_syscall_setup
         ;;
-        ssm psr.i
-        movl r2=ia64_ret_from_syscall
+        mov ar.rsc=0x3                  // set eager mode, pl 0, little-endian, loadrs=0
+        mov rp=r14                              // set the real return addr
+        nop.i 0
         ;;
-        mov rp=r2                               // set the real return addr
+        ssm psr.i
         tbit.z p8,p0=r3,TIF_SYSCALL_TRACE
-        ;;
 (p10)   br.cond.spnt.many ia64_ret_from_syscall // p10==true means out registers are more than 8
+
+        nop.m 0
 (p8)    br.call.sptk.many b6=b6         // ignore this return addr
-        br.cond.sptk ia64_trace_syscall
+        br.cond.spnt ia64_trace_syscall
 END(fsys_bubble_down)
 
         .rodata