[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>
This commit is contained in:
David Mosberger-Tang
Tony Luck
parent
c03f058fbf
commit
f8fa5448fc
1 changed files with 107 additions and 68 deletions
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@ -687,82 +687,118 @@ ENTRY(break_fault)
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* to prevent leaking bits from kernel to user level.
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*/
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DBG_FAULT(11)
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mov r16=IA64_KR(CURRENT) // r16 = current task; 12 cycle read lat.
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mov r17=cr.iim
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mov r18=__IA64_BREAK_SYSCALL
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mov r21=ar.fpsr
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mov r29=cr.ipsr
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mov r19=b6
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mov r25=ar.unat
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mov r27=ar.rsc
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mov r26=ar.pfs
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mov r28=cr.iip
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mov r31=pr // prepare to save predicates
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mov r20=r1
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mov.m r16=IA64_KR(CURRENT) // M2 r16 <- current task (12 cyc)
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mov r29=cr.ipsr // M2 (12 cyc)
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mov r31=pr // I0 (2 cyc)
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mov r17=cr.iim // M2 (2 cyc)
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mov.m r27=ar.rsc // M2 (12 cyc)
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mov r18=__IA64_BREAK_SYSCALL // A
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mov.m ar.rsc=0 // M2
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mov.m r21=ar.fpsr // M2 (12 cyc)
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mov r19=b6 // I0 (2 cyc)
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;;
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mov.m r23=ar.bspstore // M2 (12 cyc)
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mov.m r24=ar.rnat // M2 (5 cyc)
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mov.i r26=ar.pfs // I0 (2 cyc)
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invala // M0|1
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nop.m 0 // M
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mov r20=r1 // A save r1
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nop.m 0
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movl r30=sys_call_table // X
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mov r28=cr.iip // M2 (2 cyc)
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cmp.eq p0,p7=r18,r17 // I0 is this a system call?
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(p7) br.cond.spnt non_syscall // B no ->
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//
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// From this point on, we are definitely on the syscall-path
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// and we can use (non-banked) scratch registers.
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//
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///////////////////////////////////////////////////////////////////////
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mov r1=r16 // A move task-pointer to "addl"-addressable reg
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mov r2=r16 // A setup r2 for ia64_syscall_setup
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add r9=TI_FLAGS+IA64_TASK_SIZE,r16 // A r9 = ¤t_thread_info()->flags
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adds r16=IA64_TASK_THREAD_ON_USTACK_OFFSET,r16
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cmp.eq p0,p7=r18,r17 // is this a system call? (p7 <- false, if so)
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(p7) br.cond.spnt non_syscall
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;;
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ld1 r17=[r16] // load current->thread.on_ustack flag
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st1 [r16]=r0 // clear current->thread.on_ustack flag
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add r1=-IA64_TASK_THREAD_ON_USTACK_OFFSET,r16 // set r1 for MINSTATE_START_SAVE_MIN_VIRT
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;;
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invala
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/* adjust return address so we skip over the break instruction: */
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extr.u r8=r29,41,2 // extract ei field from cr.ipsr
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;;
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cmp.eq p6,p7=2,r8 // isr.ei==2?
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mov r2=r1 // setup r2 for ia64_syscall_setup
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;;
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(p6) mov r8=0 // clear ei to 0
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(p6) adds r28=16,r28 // switch cr.iip to next bundle cr.ipsr.ei wrapped
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(p7) adds r8=1,r8 // increment ei to next slot
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;;
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cmp.eq pKStk,pUStk=r0,r17 // are we in kernel mode already?
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dep r29=r8,r29,41,2 // insert new ei into cr.ipsr
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;;
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// switch from user to kernel RBS:
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MINSTATE_START_SAVE_MIN_VIRT
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br.call.sptk.many b7=ia64_syscall_setup
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;;
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MINSTATE_END_SAVE_MIN_VIRT // switch to bank 1
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ssm psr.ic | PSR_DEFAULT_BITS
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;;
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srlz.i // guarantee that interruption collection is on
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adds r15=-1024,r15 // A subtract 1024 from syscall number
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mov r3=NR_syscalls - 1
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;;
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(p15) ssm psr.i // restore psr.i
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// p10==true means out registers are more than 8 or r15's Nat is true
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(p10) br.cond.spnt.many ia64_ret_from_syscall
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;;
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movl r16=sys_call_table
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ld1.bias r17=[r16] // M0|1 r17 = current->thread.on_ustack flag
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ld4 r9=[r9] // M0|1 r9 = current_thread_info()->flags
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extr.u r8=r29,41,2 // I0 extract ei field from cr.ipsr
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adds r15=-1024,r15 // r15 contains the syscall number---subtract 1024
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movl r2=ia64_ret_from_syscall
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shladd r30=r15,3,r30 // A r30 = sys_call_table + 8*(syscall-1024)
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addl r22=IA64_RBS_OFFSET,r1 // A compute base of RBS
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cmp.leu p6,p7=r15,r3 // A syscall number in range?
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;;
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shladd r20=r15,3,r16 // r20 = sys_call_table + 8*(syscall-1024)
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cmp.leu p6,p7=r15,r3 // (syscall > 0 && syscall < 1024 + NR_syscalls) ?
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mov rp=r2 // set the real return addr
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;;
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(p6) ld8 r20=[r20] // load address of syscall entry point
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(p7) movl r20=sys_ni_syscall
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add r2=TI_FLAGS+IA64_TASK_SIZE,r13
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lfetch.fault.excl.nt1 [r22] // M0|1 prefetch RBS
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(p6) ld8 r30=[r30] // M0|1 load address of syscall entry point
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tnat.nz.or p7,p0=r15 // I0 is syscall nr a NaT?
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mov.m ar.bspstore=r22 // M2 switch to kernel RBS
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cmp.eq p8,p9=2,r8 // A isr.ei==2?
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;;
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ld4 r2=[r2] // r2 = current_thread_info()->flags
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(p8) mov r8=0 // A clear ei to 0
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(p7) movl r30=sys_ni_syscall // X
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(p8) adds r28=16,r28 // A switch cr.iip to next bundle
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(p9) adds r8=1,r8 // A increment ei to next slot
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nop.i 0
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;;
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and r2=_TIF_SYSCALL_TRACEAUDIT,r2 // mask trace or audit
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mov.m r25=ar.unat // M2 (5 cyc)
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dep r29=r8,r29,41,2 // I0 insert new ei into cr.ipsr
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adds r15=1024,r15 // A restore original syscall number
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//
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// If any of the above loads miss in L1D, we'll stall here until
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// the data arrives.
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//
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///////////////////////////////////////////////////////////////////////
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st1 [r16]=r0 // M2|3 clear current->thread.on_ustack flag
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mov b6=r30 // I0 setup syscall handler branch reg early
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cmp.eq pKStk,pUStk=r0,r17 // A were we on kernel stacks already?
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and r9=_TIF_SYSCALL_TRACEAUDIT,r9 // A mask trace or audit
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mov r18=ar.bsp // M2 (12 cyc)
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(pKStk) br.cond.spnt .break_fixup // B we're already in kernel-mode -- fix up RBS
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;;
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cmp.eq p8,p0=r2,r0
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mov b6=r20
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.back_from_break_fixup:
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(pUStk) addl r1=IA64_STK_OFFSET-IA64_PT_REGS_SIZE,r1 // A compute base of memory stack
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cmp.eq p14,p0=r9,r0 // A are syscalls being traced/audited?
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br.call.sptk.many b7=ia64_syscall_setup // B
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1:
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mov ar.rsc=0x3 // M2 set eager mode, pl 0, LE, loadrs=0
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nop 0
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bsw.1 // B (6 cyc) regs are saved, switch to bank 1
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;;
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(p8) br.call.sptk.many b6=b6 // ignore this return addr
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br.cond.sptk ia64_trace_syscall
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ssm psr.ic | PSR_DEFAULT_BITS // M2 now it's safe to re-enable intr.-collection
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movl r3=ia64_ret_from_syscall // X
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;;
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srlz.i // M0 ensure interruption collection is on
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mov rp=r3 // I0 set the real return addr
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(p10) br.cond.spnt.many ia64_ret_from_syscall // B return if bad call-frame or r15 is a NaT
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(p15) ssm psr.i // M2 restore psr.i
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(p14) br.call.sptk.many b6=b6 // B invoke syscall-handker (ignore return addr)
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br.cond.spnt.many ia64_trace_syscall // B do syscall-tracing thingamagic
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// NOT REACHED
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///////////////////////////////////////////////////////////////////////
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// On entry, we optimistically assumed that we're coming from user-space.
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// For the rare cases where a system-call is done from within the kernel,
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// we fix things up at this point:
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.break_fixup:
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add r1=-IA64_PT_REGS_SIZE,sp // A allocate space for pt_regs structure
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mov ar.rnat=r24 // M2 restore kernel's AR.RNAT
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;;
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mov ar.bspstore=r23 // M2 restore kernel's AR.BSPSTORE
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br.cond.sptk .back_from_break_fixup
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END(break_fault)
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.org ia64_ivt+0x3000
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@ -837,8 +873,6 @@ END(interrupt)
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* - r31: saved pr
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* - b0: original contents (to be saved)
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* On exit:
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* - executing on bank 1 registers
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* - psr.ic enabled, interrupts restored
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* - p10: TRUE if syscall is invoked with more than 8 out
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* registers or r15's Nat is true
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* - r1: kernel's gp
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@ -846,8 +880,11 @@ END(interrupt)
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* - r8: -EINVAL if p10 is true
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* - r12: points to kernel stack
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* - r13: points to current task
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* - r14: preserved (same as on entry)
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* - p13: preserved
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* - p15: TRUE if interrupts need to be re-enabled
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* - ar.fpsr: set to kernel settings
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* - b6: preserved (same as on entry)
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*/
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GLOBAL_ENTRY(ia64_syscall_setup)
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#if PT(B6) != 0
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@ -915,7 +952,7 @@ GLOBAL_ENTRY(ia64_syscall_setup)
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(p13) mov in5=-1
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;;
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st8 [r16]=r21,PT(R8)-PT(AR_FPSR) // save ar.fpsr
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tnat.nz p14,p0=in6
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tnat.nz p13,p0=in6
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cmp.lt p10,p9=r11,r8 // frame size can't be more than local+8
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;;
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mov r8=1
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@ -930,7 +967,7 @@ GLOBAL_ENTRY(ia64_syscall_setup)
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movl r1=__gp // establish kernel global pointer
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;;
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st8 [r16]=r8 // ensure pt_regs.r8 != 0 (see handle_syscall_error)
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(p14) mov in6=-1
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(p13) mov in6=-1
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(p8) mov in7=-1
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cmp.eq pSys,pNonSys=r0,r0 // set pSys=1, pNonSys=0
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@ -1002,6 +1039,8 @@ END(dispatch_illegal_op_fault)
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FAULT(17)
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ENTRY(non_syscall)
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mov ar.rsc=r27 // restore ar.rsc before SAVE_MIN_WITH_COVER
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;;
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SAVE_MIN_WITH_COVER
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// There is no particular reason for this code to be here, other than that
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