diff options
Diffstat (limited to 'arch/alpha/lib/ev6-clear_user.S')
| -rw-r--r-- | arch/alpha/lib/ev6-clear_user.S | 225 |
1 files changed, 225 insertions, 0 deletions
diff --git a/arch/alpha/lib/ev6-clear_user.S b/arch/alpha/lib/ev6-clear_user.S new file mode 100644 index 0000000..4f42a16 --- /dev/null +++ b/arch/alpha/lib/ev6-clear_user.S @@ -0,0 +1,225 @@ +/* + * arch/alpha/lib/ev6-clear_user.S + * 21264 version contributed by Rick Gorton <rick.gorton@alpha-processor.com> + * + * Zero user space, handling exceptions as we go. + * + * We have to make sure that $0 is always up-to-date and contains the + * right "bytes left to zero" value (and that it is updated only _after_ + * a successful copy). There is also some rather minor exception setup + * stuff. + * + * NOTE! This is not directly C-callable, because the calling semantics + * are different: + * + * Inputs: + * length in $0 + * destination address in $6 + * exception pointer in $7 + * return address in $28 (exceptions expect it there) + * + * Outputs: + * bytes left to copy in $0 + * + * Clobbers: + * $1,$2,$3,$4,$5,$6 + * + * Much of the information about 21264 scheduling/coding comes from: + * Compiler Writer's Guide for the Alpha 21264 + * abbreviated as 'CWG' in other comments here + * ftp.digital.com/pub/Digital/info/semiconductor/literature/dsc-library.html + * Scheduling notation: + * E - either cluster + * U - upper subcluster; U0 - subcluster U0; U1 - subcluster U1 + * L - lower subcluster; L0 - subcluster L0; L1 - subcluster L1 + * Try not to change the actual algorithm if possible for consistency. + * Determining actual stalls (other than slotting) doesn't appear to be easy to do. + * From perusing the source code context where this routine is called, it is + * a fair assumption that significant fractions of entire pages are zeroed, so + * it's going to be worth the effort to hand-unroll a big loop, and use wh64. + * ASSUMPTION: + * The believed purpose of only updating $0 after a store is that a signal + * may come along during the execution of this chunk of code, and we don't + * want to leave a hole (and we also want to avoid repeating lots of work) + */ + +/* Allow an exception for an insn; exit if we get one. */ +#define EX(x,y...) \ + 99: x,##y; \ + .section __ex_table,"a"; \ + .long 99b - .; \ + lda $31, $exception-99b($31); \ + .previous + + .set noat + .set noreorder + .align 4 + + .globl __do_clear_user + .ent __do_clear_user + .frame $30, 0, $28 + .prologue 0 + + # Pipeline info : Slotting & Comments +__do_clear_user: + and $6, 7, $4 # .. E .. .. : find dest head misalignment + beq $0, $zerolength # U .. .. .. : U L U L + + addq $0, $4, $1 # .. .. .. E : bias counter + and $1, 7, $2 # .. .. E .. : number of misaligned bytes in tail +# Note - we never actually use $2, so this is a moot computation +# and we can rewrite this later... + srl $1, 3, $1 # .. E .. .. : number of quadwords to clear + beq $4, $headalign # U .. .. .. : U L U L + +/* + * Head is not aligned. Write (8 - $4) bytes to head of destination + * This means $6 is known to be misaligned + */ + EX( ldq_u $5, 0($6) ) # .. .. .. L : load dst word to mask back in + beq $1, $onebyte # .. .. U .. : sub-word store? + mskql $5, $6, $5 # .. U .. .. : take care of misaligned head + addq $6, 8, $6 # E .. .. .. : L U U L + + EX( stq_u $5, -8($6) ) # .. .. .. L : + subq $1, 1, $1 # .. .. E .. : + addq $0, $4, $0 # .. E .. .. : bytes left -= 8 - misalignment + subq $0, 8, $0 # E .. .. .. : U L U L + + .align 4 +/* + * (The .align directive ought to be a moot point) + * values upon initial entry to the loop + * $1 is number of quadwords to clear (zero is a valid value) + * $2 is number of trailing bytes (0..7) ($2 never used...) + * $6 is known to be aligned 0mod8 + */ +$headalign: + subq $1, 16, $4 # .. .. .. E : If < 16, we can not use the huge loop + and $6, 0x3f, $2 # .. .. E .. : Forward work for huge loop + subq $2, 0x40, $3 # .. E .. .. : bias counter (huge loop) + blt $4, $trailquad # U .. .. .. : U L U L + +/* + * We know that we're going to do at least 16 quads, which means we are + * going to be able to use the large block clear loop at least once. + * Figure out how many quads we need to clear before we are 0mod64 aligned + * so we can use the wh64 instruction. + */ + + nop # .. .. .. E + nop # .. .. E .. + nop # .. E .. .. + beq $3, $bigalign # U .. .. .. : U L U L : Aligned 0mod64 + +$alignmod64: + EX( stq_u $31, 0($6) ) # .. .. .. L + addq $3, 8, $3 # .. .. E .. + subq $0, 8, $0 # .. E .. .. + nop # E .. .. .. : U L U L + + nop # .. .. .. E + subq $1, 1, $1 # .. .. E .. + addq $6, 8, $6 # .. E .. .. + blt $3, $alignmod64 # U .. .. .. : U L U L + +$bigalign: +/* + * $0 is the number of bytes left + * $1 is the number of quads left + * $6 is aligned 0mod64 + * we know that we'll be taking a minimum of one trip through + * CWG Section 3.7.6: do not expect a sustained store rate of > 1/cycle + * We are _not_ going to update $0 after every single store. That + * would be silly, because there will be cross-cluster dependencies + * no matter how the code is scheduled. By doing it in slightly + * staggered fashion, we can still do this loop in 5 fetches + * The worse case will be doing two extra quads in some future execution, + * in the event of an interrupted clear. + * Assumes the wh64 needs to be for 2 trips through the loop in the future + * The wh64 is issued on for the starting destination address for trip +2 + * through the loop, and if there are less than two trips left, the target + * address will be for the current trip. + */ + nop # E : + nop # E : + nop # E : + bis $6,$6,$3 # E : U L U L : Initial wh64 address is dest + /* This might actually help for the current trip... */ + +$do_wh64: + wh64 ($3) # .. .. .. L1 : memory subsystem hint + subq $1, 16, $4 # .. .. E .. : Forward calculation - repeat the loop? + EX( stq_u $31, 0($6) ) # .. L .. .. + subq $0, 8, $0 # E .. .. .. : U L U L + + addq $6, 128, $3 # E : Target address of wh64 + EX( stq_u $31, 8($6) ) # L : + EX( stq_u $31, 16($6) ) # L : + subq $0, 16, $0 # E : U L L U + + nop # E : + EX( stq_u $31, 24($6) ) # L : + EX( stq_u $31, 32($6) ) # L : + subq $0, 168, $5 # E : U L L U : two trips through the loop left? + /* 168 = 192 - 24, since we've already completed some stores */ + + subq $0, 16, $0 # E : + EX( stq_u $31, 40($6) ) # L : + EX( stq_u $31, 48($6) ) # L : + cmovlt $5, $6, $3 # E : U L L U : Latency 2, extra mapping cycle + + subq $1, 8, $1 # E : + subq $0, 16, $0 # E : + EX( stq_u $31, 56($6) ) # L : + nop # E : U L U L + + nop # E : + subq $0, 8, $0 # E : + addq $6, 64, $6 # E : + bge $4, $do_wh64 # U : U L U L + +$trailquad: + # zero to 16 quadwords left to store, plus any trailing bytes + # $1 is the number of quadwords left to go. + # + nop # .. .. .. E + nop # .. .. E .. + nop # .. E .. .. + beq $1, $trailbytes # U .. .. .. : U L U L : Only 0..7 bytes to go + +$onequad: + EX( stq_u $31, 0($6) ) # .. .. .. L + subq $1, 1, $1 # .. .. E .. + subq $0, 8, $0 # .. E .. .. + nop # E .. .. .. : U L U L + + nop # .. .. .. E + nop # .. .. E .. + addq $6, 8, $6 # .. E .. .. + bgt $1, $onequad # U .. .. .. : U L U L + + # We have an unknown number of bytes left to go. +$trailbytes: + nop # .. .. .. E + nop # .. .. E .. + nop # .. E .. .. + beq $0, $zerolength # U .. .. .. : U L U L + + # $0 contains the number of bytes left to copy (0..31) + # so we will use $0 as the loop counter + # We know for a fact that $0 > 0 zero due to previous context +$onebyte: + EX( stb $31, 0($6) ) # .. .. .. L + subq $0, 1, $0 # .. .. E .. : + addq $6, 1, $6 # .. E .. .. : + bgt $0, $onebyte # U .. .. .. : U L U L + +$zerolength: +$exception: # Destination for exception recovery(?) + nop # .. .. .. E : + nop # .. .. E .. : + nop # .. E .. .. : + ret $31, ($28), 1 # L0 .. .. .. : L U L U + .end __do_clear_user + |
