[IA64] relax per-cpu TLB requirement to DTC

Instead of pinning per-cpu TLB into a DTR, use DTC.  This will free up
one TLB entry for application, or even kernel if access pattern to
per-cpu data area has high temporal locality.

Since per-cpu is mapped at the top of region 7 address, we just need to
add special case in alt_dtlb_miss.  The physical address of per-cpu data
is already conveniently stored in IA64_KR(PER_CPU_DATA).  Latency for
alt_dtlb_miss is not affected as we can hide all the latency.  It was
measured that alt_dtlb_miss handler has 23 cycles latency before and
after the patch.

The performance effect is massive for applications that put lots of tlb
pressure on CPU.  Workload environment like database online transaction
processing or application uses tera-byte of memory would benefit the most.
Measurement with industry standard database benchmark shown an upward
of 1.6% gain.  While smaller workloads like cpu, java also showing small
improvement.

Signed-off-by: Ken Chen <kenneth.w.chen@intel.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>

1 files changed, 14 insertions, 5 deletions

diff --git a/arch/ia64/kernel/ivt.S b/arch/ia64/kernel/ivt.S
index 6b7fcbd3f6f1..34f44d8be00d 100644
--- a/arch/ia64/kernel/ivt.S
+++ b/arch/ia64/kernel/ivt.S
@@ -374,6 +374,7 @@ ENTRY(alt_dtlb_miss)
         movl r19=(((1 << IA64_MAX_PHYS_BITS) - 1) & ~0xfff)
         mov r21=cr.ipsr
         mov r31=pr
+        mov r24=PERCPU_ADDR
         ;;
 #ifdef CONFIG_DISABLE_VHPT
         shr.u r22=r16,61                        // get the region number into r21
@@ -386,22 +387,30 @@ ENTRY(alt_dtlb_miss)
 (p8)    mov r29=b0                              // save b0
 (p8)    br.cond.dptk dtlb_fault
 #endif
+        cmp.ge p10,p11=r16,r24                  // access to per_cpu_data?
+        tbit.z p12,p0=r16,61                    // access to region 6?
+        mov r25=PERCPU_PAGE_SHIFT << 2
+        mov r26=PERCPU_PAGE_SIZE
+        nop.m 0
+        nop.b 0
+        ;;
+(p10)   mov r19=IA64_KR(PER_CPU_DATA)
+(p11)   and r19=r19,r16                         // clear non-ppn fields
         extr.u r23=r21,IA64_PSR_CPL0_BIT,2      // extract psr.cpl
         and r22=IA64_ISR_CODE_MASK,r20          // get the isr.code field
         tbit.nz p6,p7=r20,IA64_ISR_SP_BIT       // is speculation bit on?
-        shr.u r18=r16,57                        // move address bit 61 to bit 4
-        and r19=r19,r16                         // clear ed, reserved bits, and PTE control bits
         tbit.nz p9,p0=r20,IA64_ISR_NA_BIT       // is non-access bit on?
         ;;
-        andcm r18=0x10,r18      // bit 4=~address-bit(61)
+(p10)   sub r19=r19,r26
+(p10)   mov cr.itir=r25
         cmp.ne p8,p0=r0,r23
 (p9)    cmp.eq.or.andcm p6,p7=IA64_ISR_CODE_LFETCH,r22  // check isr.code field
+(p12)   dep r17=-1,r17,4,1                      // set ma=UC for region 6 addr
 (p8)    br.cond.spnt page_fault
 
         dep r21=-1,r21,IA64_PSR_ED_BIT,1
-        or r19=r19,r17          // insert PTE control bits into r19
         ;;
-        or r19=r19,r18          // set bit 4 (uncached) if the access was to region 6
+        or r19=r19,r17          // insert PTE control bits into r19
 (p6)    mov cr.ipsr=r21
         ;;
 (p7)    itc.d r19               // insert the TLB entry