[IA64] Reschedule break_fault() for better performance.

This patch reorganizes break_fault() to optimistically assume that a
system-call is being performed from user-space (which is almost always
the case).  If it turns out that (a) we're not being called due to a
system call or (b) we're being called from within the kernel, we fixup
the no-longer-valid assumptions in non_syscall() and .break_fixup(),
respectively.

With this approach, there are 3 major phases:

 - Phase 1: Read various control & application registers, in
	    particular the current task pointer from AR.K6.
 - Phase 2: Do all memory loads (load system-call entry,
	    load current_thread_info()->flags, prefetch
	    kernel register-backing store) and switch
	    to kernel register-stack.
 - Phase 3: Call ia64_syscall_setup() and invoke
	    syscall-handler.

Good for 26-30 cycles of improvement on break-based syscall-path.

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

1 files changed, 106 insertions, 67 deletions

diff --git a/arch/ia64/kernel/ivt.S b/arch/ia64/kernel/ivt.S
index dc78c356ddd0..386087edabf2 100644
--- a/arch/ia64/kernel/ivt.S
+++ b/arch/ia64/kernel/ivt.S
@@ -687,82 +687,118 @@ ENTRY(break_fault)
          * to prevent leaking bits from kernel to user level.
          */
         DBG_FAULT(11)
-        mov r16=IA64_KR(CURRENT)                // r16 = current task; 12 cycle read lat.
-        mov r17=cr.iim
-        mov r18=__IA64_BREAK_SYSCALL
-        mov r21=ar.fpsr
-        mov r29=cr.ipsr
-        mov r19=b6
-        mov r25=ar.unat
-        mov r27=ar.rsc
-        mov r26=ar.pfs
-        mov r28=cr.iip
-        mov r31=pr                              // prepare to save predicates
-        mov r20=r1
-        ;;
+        mov.m r16=IA64_KR(CURRENT)              // M2 r16 <- current task (12 cyc)
+        mov r29=cr.ipsr                         // M2 (12 cyc)
+        mov r31=pr                              // I0 (2 cyc)
+
+        mov r17=cr.iim                          // M2 (2 cyc)
+        mov.m r27=ar.rsc                        // M2 (12 cyc)
+        mov r18=__IA64_BREAK_SYSCALL            // A
+
+        mov.m ar.rsc=0                          // M2
+        mov.m r21=ar.fpsr                       // M2 (12 cyc)
+        mov r19=b6                              // I0 (2 cyc)
+        ;;
+        mov.m r23=ar.bspstore                   // M2 (12 cyc)
+        mov.m r24=ar.rnat                       // M2 (5 cyc)
+        mov.i r26=ar.pfs                        // I0 (2 cyc)
+
+        invala                                  // M0|1
+        nop.m 0                                 // M
+        mov r20=r1                              // A                    save r1
+
+        nop.m 0
+        movl r30=sys_call_table                 // X
+
+        mov r28=cr.iip                          // M2 (2 cyc)
+        cmp.eq p0,p7=r18,r17                    // I0 is this a system call?
+(p7)    br.cond.spnt non_syscall                // B  no ->
+        //
+        // From this point on, we are definitely on the syscall-path
+        // and we can use (non-banked) scratch registers.
+        //
+///////////////////////////////////////////////////////////////////////
+        mov r1=r16                              // A    move task-pointer to "addl"-addressable reg
+        mov r2=r16                              // A    setup r2 for ia64_syscall_setup
+        add r9=TI_FLAGS+IA64_TASK_SIZE,r16      // A    r9 = &current_thread_info()->flags
+
         adds r16=IA64_TASK_THREAD_ON_USTACK_OFFSET,r16
-        cmp.eq p0,p7=r18,r17                    // is this a system call? (p7 <- false, if so)
-(p7)    br.cond.spnt non_syscall
+        adds r15=-1024,r15                      // A    subtract 1024 from syscall number
+        mov r3=NR_syscalls - 1
         ;;
-        ld1 r17=[r16]                           // load current->thread.on_ustack flag
-        st1 [r16]=r0                            // clear current->thread.on_ustack flag
-        add r1=-IA64_TASK_THREAD_ON_USTACK_OFFSET,r16   // set r1 for MINSTATE_START_SAVE_MIN_VIRT
+        ld1.bias r17=[r16]                      // M0|1 r17 = current->thread.on_ustack flag
+        ld4 r9=[r9]                             // M0|1 r9 = current_thread_info()->flags
+        extr.u r8=r29,41,2                      // I0   extract ei field from cr.ipsr
+
+        shladd r30=r15,3,r30                    // A    r30 = sys_call_table + 8*(syscall-1024)
+        addl r22=IA64_RBS_OFFSET,r1             // A    compute base of RBS
+        cmp.leu p6,p7=r15,r3                    // A    syscall number in range?
         ;;
-        invala
 
-        /* adjust return address so we skip over the break instruction: */
+        lfetch.fault.excl.nt1 [r22]             // M0|1 prefetch RBS
+(p6)    ld8 r30=[r30]                           // M0|1 load address of syscall entry point
+        tnat.nz.or p7,p0=r15                    // I0   is syscall nr a NaT?
 
-        extr.u r8=r29,41,2                      // extract ei field from cr.ipsr
-        ;;
-        cmp.eq p6,p7=2,r8                       // isr.ei==2?
-        mov r2=r1                               // setup r2 for ia64_syscall_setup
-        ;;
-(p6)    mov r8=0                                // clear ei to 0
-(p6)    adds r28=16,r28                         // switch cr.iip to next bundle cr.ipsr.ei wrapped
-(p7)    adds r8=1,r8                            // increment ei to next slot
-        ;;
-        cmp.eq pKStk,pUStk=r0,r17               // are we in kernel mode already?
-        dep r29=r8,r29,41,2                     // insert new ei into cr.ipsr
+        mov.m ar.bspstore=r22                   // M2   switch to kernel RBS
+        cmp.eq p8,p9=2,r8                       // A    isr.ei==2?
         ;;
 
-        // switch from user to kernel RBS:
-        MINSTATE_START_SAVE_MIN_VIRT
-        br.call.sptk.many b7=ia64_syscall_setup
-        ;;
-        MINSTATE_END_SAVE_MIN_VIRT              // switch to bank 1
-        ssm psr.ic | PSR_DEFAULT_BITS
-        ;;
-        srlz.i                                  // guarantee that interruption collection is on
-        mov r3=NR_syscalls - 1
-        ;;
-(p15)   ssm psr.i                               // restore psr.i
-        // p10==true means out registers are more than 8 or r15's Nat is true
-(p10)   br.cond.spnt.many ia64_ret_from_syscall
-        ;;
-        movl r16=sys_call_table
+(p8)    mov r8=0                                // A    clear ei to 0
+(p7)    movl r30=sys_ni_syscall                 // X
 
-        adds r15=-1024,r15                      // r15 contains the syscall number---subtract 1024
-        movl r2=ia64_ret_from_syscall
-        ;;
-        shladd r20=r15,3,r16                    // r20 = sys_call_table + 8*(syscall-1024)
-        cmp.leu p6,p7=r15,r3                    // (syscall > 0 && syscall < 1024 + NR_syscalls) ?
-        mov rp=r2                               // set the real return addr
+(p8)    adds r28=16,r28                         // A    switch cr.iip to next bundle
+(p9)    adds r8=1,r8                            // A    increment ei to next slot
+        nop.i 0
         ;;
-(p6)    ld8 r20=[r20]                           // load address of syscall entry point
-(p7)    movl r20=sys_ni_syscall
 
-        add r2=TI_FLAGS+IA64_TASK_SIZE,r13
-        ;;
-        ld4 r2=[r2]                             // r2 = current_thread_info()->flags
-        ;;
-        and r2=_TIF_SYSCALL_TRACEAUDIT,r2       // mask trace or audit
+        mov.m r25=ar.unat                       // M2 (5 cyc)
+        dep r29=r8,r29,41,2                     // I0   insert new ei into cr.ipsr
+        adds r15=1024,r15                       // A    restore original syscall number
+        //
+        // If any of the above loads miss in L1D, we'll stall here until
+        // the data arrives.
+        //
+///////////////////////////////////////////////////////////////////////
+        st1 [r16]=r0                            // M2|3 clear current->thread.on_ustack flag
+        mov b6=r30                              // I0   setup syscall handler branch reg early
+        cmp.eq pKStk,pUStk=r0,r17               // A    were we on kernel stacks already?
+
+        and r9=_TIF_SYSCALL_TRACEAUDIT,r9       // A    mask trace or audit
+        mov r18=ar.bsp                          // M2 (12 cyc)
+(pKStk) br.cond.spnt .break_fixup               // B    we're already in kernel-mode -- fix up RBS
+        ;;
+.back_from_break_fixup:
+(pUStk) addl r1=IA64_STK_OFFSET-IA64_PT_REGS_SIZE,r1 // A    compute base of memory stack
+        cmp.eq p14,p0=r9,r0                     // A    are syscalls being traced/audited?
+        br.call.sptk.many b7=ia64_syscall_setup // B
+1:
+        mov ar.rsc=0x3                          // M2   set eager mode, pl 0, LE, loadrs=0
+        nop 0
+        bsw.1                                   // B (6 cyc) regs are saved, switch to bank 1
         ;;
-        cmp.eq p8,p0=r2,r0
-        mov b6=r20
+
+        ssm psr.ic | PSR_DEFAULT_BITS           // M2   now it's safe to re-enable intr.-collection
+        movl r3=ia64_ret_from_syscall           // X
         ;;
-(p8)    br.call.sptk.many b6=b6                 // ignore this return addr
-        br.cond.sptk ia64_trace_syscall
+
+        srlz.i                                  // M0   ensure interruption collection is on
+        mov rp=r3                               // I0   set the real return addr
+(p10)   br.cond.spnt.many ia64_ret_from_syscall // B    return if bad call-frame or r15 is a NaT
+
+(p15)   ssm psr.i                               // M2   restore psr.i
+(p14)   br.call.sptk.many b6=b6                 // B    invoke syscall-handker (ignore return addr)
+        br.cond.spnt.many ia64_trace_syscall    // B    do syscall-tracing thingamagic
         // NOT REACHED
+///////////////////////////////////////////////////////////////////////
+        // On entry, we optimistically assumed that we're coming from user-space.
+        // For the rare cases where a system-call is done from within the kernel,
+        // we fix things up at this point:
+.break_fixup:
+        add r1=-IA64_PT_REGS_SIZE,sp            // A    allocate space for pt_regs structure
+        mov ar.rnat=r24                         // M2   restore kernel's AR.RNAT
+        ;;
+        mov ar.bspstore=r23                     // M2   restore kernel's AR.BSPSTORE
+        br.cond.sptk .back_from_break_fixup
 END(break_fault)
 
         .org ia64_ivt+0x3000
@@ -837,8 +873,6 @@ END(interrupt)
          *      - r31: saved pr
          *      -  b0: original contents (to be saved)
          * On exit:
-         *      - executing on bank 1 registers
-         *      - psr.ic enabled, interrupts restored
          *      -  p10: TRUE if syscall is invoked with more than 8 out
          *              registers or r15's Nat is true
          *      -  r1: kernel's gp
@@ -846,8 +880,11 @@ END(interrupt)
          *      -  r8: -EINVAL if p10 is true
          *      - r12: points to kernel stack
          *      - r13: points to current task
+         *      - r14: preserved (same as on entry)
+         *      - p13: preserved
          *      - p15: TRUE if interrupts need to be re-enabled
          *      - ar.fpsr: set to kernel settings
+         *      -  b6: preserved (same as on entry)
          */
 GLOBAL_ENTRY(ia64_syscall_setup)
 #if PT(B6) != 0
@@ -915,7 +952,7 @@ GLOBAL_ENTRY(ia64_syscall_setup)
 (p13)   mov in5=-1
         ;;
         st8 [r16]=r21,PT(R8)-PT(AR_FPSR)        // save ar.fpsr
-        tnat.nz p14,p0=in6
+        tnat.nz p13,p0=in6
         cmp.lt p10,p9=r11,r8    // frame size can't be more than local+8
         ;;
         mov r8=1
@@ -930,7 +967,7 @@ GLOBAL_ENTRY(ia64_syscall_setup)
         movl r1=__gp                            // establish kernel global pointer
         ;;
         st8 [r16]=r8            // ensure pt_regs.r8 != 0 (see handle_syscall_error)
-(p14)   mov in6=-1
+(p13)   mov in6=-1
 (p8)    mov in7=-1
 
         cmp.eq pSys,pNonSys=r0,r0               // set pSys=1, pNonSys=0
@@ -1002,6 +1039,8 @@ END(dispatch_illegal_op_fault)
         FAULT(17)
 
 ENTRY(non_syscall)
+        mov ar.rsc=r27                  // restore ar.rsc before SAVE_MIN_WITH_COVER
+        ;;
         SAVE_MIN_WITH_COVER
 
         // There is no particular reason for this code to be here, other than that