From: David Mosberger-Tang Date: Thu, 28 Apr 2005 04:20:51 +0000 (-0700) Subject: [IA64] Reschedule fsys_bubble_down(). X-Git-Tag: v2.6.13-rc2~59^2~14^2~6 X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=1ba7be7d691f6df2557d39c5b1a2e14c32e5dd20;p=linux-2.6 [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 Signed-off-by: Tony Luck --- diff --git a/arch/ia64/kernel/fsys.S b/arch/ia64/kernel/fsys.S index 0d8650f7fc..57c6556b1e 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