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/*
 * McKinley-optimized version of copy_page().
 *
 * Copyright (C) 2002 Hewlett-Packard Co
 *      David Mosberger <davidm@hpl.hp.com>
 *
 * Inputs:
 *      in0:    address of target page
 *      in1:    address of source page
 * Output:
 *      no return value
 *
 * General idea:
 *      - use regular loads and stores to prefetch data to avoid consuming M-slot just for
 *        lfetches => good for in-cache performance
 *      - avoid l2 bank-conflicts by not storing into the same 16-byte bank within a single
 *        cycle
 *
 * Principle of operation:
 *      First, note that L1 has a line-size of 64 bytes and L2 a line-size of 128 bytes.
 *      To avoid secondary misses in L2, we prefetch both source and destination with a line-size
 *      of 128 bytes.  When both of these lines are in the L2 and the first half of the
 *      source line is in L1, we start copying the remaining words.  The second half of the
 *      source line is prefetched in an earlier iteration, so that by the time we start
 *      accessing it, it's also present in the L1.
 *
 *      We use a software-pipelined loop to control the overall operation.  The pipeline
 *      has 2*PREFETCH_DIST+K stages.  The first PREFETCH_DIST stages are used for prefetching
 *      source cache-lines.  The second PREFETCH_DIST stages are used for prefetching destination
 *      cache-lines, the last K stages are used to copy the cache-line words not copied by
 *      the prefetches.  The four relevant points in the pipelined are called A, B, C, D:
 *      p[A] is TRUE if a source-line should be prefetched, p[B] is TRUE if a destination-line
 *      should be prefetched, p[C] is TRUE if the second half of an L2 line should be brought
 *      into L1D and p[D] is TRUE if a cacheline needs to be copied.
 *
 *      This all sounds very complicated, but thanks to the modulo-scheduled loop support,
 *      the resulting code is very regular and quite easy to follow (once you get the idea).
 *
 *      As a secondary optimization, the first 2*PREFETCH_DIST iterations are implemented
 *      as the separate .prefetch_loop.  Logically, this loop performs exactly like the
 *      main-loop (.line_copy), but has all known-to-be-predicated-off instructions removed,
 *      so that each loop iteration is faster (again, good for cached case).
 *
 *      When reading the code, it helps to keep the following picture in mind:
 *
 *             word 0 word 1
 *            +------+------+---
 *            | v[x] |  t1  | ^
 *            | t2   |  t3  | |
 *            | t4   |  t5  | |
 *            | t6   |  t7  | | 128 bytes
 *            | n[y] |  t9  | | (L2 cache line)
 *            | t10  |  t11 | |
 *            | t12  |  t13 | |
 *            | t14  |  t15 | v
 *            +------+------+---
 *
 *      Here, v[x] is copied by the (memory) prefetch.  n[y] is loaded at p[C]
 *      to fetch the second-half of the L2 cache line into L1, and the tX words are copied in
 *      an order that avoids bank conflicts.
 */
#include <asm/asmmacro.h>
#include <asm/page.h>

#define PREFETCH_DIST   8               // McKinley sustains 16 outstanding L2 misses (8 ld, 8 st)

#define src0            r2
#define src1            r3
#define dst0            r9
#define dst1            r10
#define src_pre_mem     r11
#define dst_pre_mem     r14
#define src_pre_l2      r15
#define dst_pre_l2      r16
#define t1              r17
#define t2              r18
#define t3              r19
#define t4              r20
#define t5              t1      // alias!
#define t6              t2      // alias!
#define t7              t3      // alias!
#define t9              t5      // alias!
#define t10             t4      // alias!
#define t11             t7      // alias!
#define t12             t6      // alias!
#define t14             t10     // alias!
#define t13             r21
#define t15             r22

#define saved_lc        r23
#define saved_pr        r24

#define A       0
#define B       (PREFETCH_DIST)
#define C       (B + PREFETCH_DIST)
#define D       (C + 3)
#define N       (D + 1)
#define Nrot    ((N + 7) & ~7)

GLOBAL_ENTRY(copy_page)
        .prologue
        alloc r8 = ar.pfs, 2, Nrot-2, 0, Nrot

        .rotr v[2*PREFETCH_DIST], n[D-C+1]
        .rotp p[N]

        .save ar.lc, saved_lc
        mov saved_lc = ar.lc
        .save pr, saved_pr
        mov saved_pr = pr
        .body

        mov src_pre_mem = in1
        mov pr.rot = 0x10000
        mov ar.ec = 1                           // special unrolled loop

        mov dst_pre_mem = in0
        mov ar.lc = 2*PREFETCH_DIST - 1

        add src_pre_l2 = 8*8, in1
        add dst_pre_l2 = 8*8, in0
        add src0 = 8, in1                       // first t1 src
        add src1 = 3*8, in1                     // first t3 src
        add dst0 = 8, in0                       // first t1 dst
        add dst1 = 3*8, in0                     // first t3 dst
        mov t1 = (PAGE_SIZE/128) - (2*PREFETCH_DIST) - 1
        nop.m 0
        nop.i 0
        ;;
        // same as .line_copy loop, but with all predicated-off instructions removed:
.prefetch_loop:
(p[A])  ld8 v[A] = [src_pre_mem], 128           // M0
(p[B])  st8 [dst_pre_mem] = v[B], 128           // M2
        br.ctop.sptk .prefetch_loop
        ;;
        cmp.eq p16, p0 = r0, r0                 // reset p16 to 1 (br.ctop cleared it to zero)
        mov ar.lc = t1                          // with 64KB pages, t1 is too big to fit in 8 bits!
        mov ar.ec = N                           // # of stages in pipeline
        ;;
.line_copy:
(p[D])  ld8 t2 = [src0], 3*8                    // M0
(p[D])  ld8 t4 = [src1], 3*8                    // M1
(p[B])  st8 [dst_pre_mem] = v[B], 128           // M2 prefetch dst from memory
(p[D])  st8 [dst_pre_l2] = n[D-C], 128          // M3 prefetch dst from L2
        ;;
(p[A])  ld8 v[A] = [src_pre_mem], 128           // M0 prefetch src from memory
(p[C])  ld8 n[0] = [src_pre_l2], 128            // M1 prefetch src from L2
(p[D])  st8 [dst0] =  t1, 8                     // M2
(p[D])  st8 [dst1] =  t3, 8                     // M3
        ;;
(p[D])  ld8  t5 = [src0], 8
(p[D])  ld8  t7 = [src1], 3*8
(p[D])  st8 [dst0] =  t2, 3*8
(p[D])  st8 [dst1] =  t4, 3*8
        ;;
(p[D])  ld8  t6 = [src0], 3*8
(p[D])  ld8 t10 = [src1], 8
(p[D])  st8 [dst0] =  t5, 8
(p[D])  st8 [dst1] =  t7, 3*8
        ;;
(p[D])  ld8  t9 = [src0], 3*8
(p[D])  ld8 t11 = [src1], 3*8
(p[D])  st8 [dst0] =  t6, 3*8
(p[D])  st8 [dst1] = t10, 8
        ;;
(p[D])  ld8 t12 = [src0], 8
(p[D])  ld8 t14 = [src1], 8
(p[D])  st8 [dst0] =  t9, 3*8
(p[D])  st8 [dst1] = t11, 3*8
        ;;
(p[D])  ld8 t13 = [src0], 4*8
(p[D])  ld8 t15 = [src1], 4*8
(p[D])  st8 [dst0] = t12, 8
(p[D])  st8 [dst1] = t14, 8
        ;;
(p[D-1])ld8  t1 = [src0], 8
(p[D-1])ld8  t3 = [src1], 8
(p[D])  st8 [dst0] = t13, 4*8
(p[D])  st8 [dst1] = t15, 4*8
        br.ctop.sptk .line_copy
        ;;
        mov ar.lc = saved_lc
        mov pr = saved_pr, -1
        br.ret.sptk.many rp
END(copy_page)