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[IA64] Reschedule fsys_bubble_down().

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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>
This commit is contained in:
David Mosberger-Tang 2005-04-27 21:20:51 -07:00 committed by Tony Luck
parent 21bc4f9b34
commit 1ba7be7d69
1 changed files with 36 additions and 43 deletions
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79
arch/ia64/kernel/fsys.S
View file

@ -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)
;;
mov psr.l=r9 // slam the door (17 cyc to srlz.i)
or r29=r8,r29 // construct cr.ipsr value to save
addl r22=IA64_RBS_OFFSET,r2 // compute base of RBS
;;
// 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)
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:
;;
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 r2=r16 // copy current task addr to addl-addressable register
adds r16=IA64_TASK_THREAD_ON_USTACK_OFFSET,r16
mov r31=pr // save pr (2 cyc)
;;
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)
addl r22=IA64_RBS_OFFSET,r2 // compute base of RBS
add r3=TI_FLAGS+IA64_TASK_SIZE,r2
;;
ld4 r3=[r3] // r2 = current_thread_info()->flags
lfetch.fault.excl.nt1 [r22]
nop.i 0
;;
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
;;
mov ar.bspstore=r22 // switch to kernel RBS
movl r8=PSR_ONE_BITS // X
;;
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
;;
mov ar.rsc=0x3 // set eager mode, pl 0, little-endian, loadrs=0
mov rp=r14 // set the real return addr
nop.i 0
;;
ssm psr.i
movl r2=ia64_ret_from_syscall
;;
mov rp=r2 // set the real return addr
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)
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