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    Subject[PATCH] ARM: copy_page.S: take into account the size of the cache line
    Date
    From: Kirill A. Shutemov <kirill@shutemov.name>

    Optimized version of copy_page() was written with assumption that cache
    line size is 32 bytes. On Cortex-A8 cache line size is 64 bytes.

    This patch tries to generalize copy_page() to work with any cache line
    size if cache line size is multiple of 16 and page size is multiple of
    two cache line size.

    Unfortunately, kernel doesn't provide a macros with correct cache size.
    L1_CACHE_SHIFT is 5 on any ARM. So we have to define macros for this
    propose by ourself.

    After this optimization we've got ~25% speedup on OMAP3(tested in
    userspace).

    There is test for kernelspace which trigger copy-on-write after fork():

    #include <stdlib.h>
    #include <string.h>
    #include <unistd.h>

    #define BUF_SIZE (10000*4096)
    #define NFORK 200

    int main(int argc, char **argv)
    {
    char *buf = malloc(BUF_SIZE);
    int i;

    memset(buf, 0, BUF_SIZE);

    for(i = 0; i < NFORK; i++) {
    if (fork()) {
    wait(NULL);
    } else {
    int j;

    for(j = 0; j < BUF_SIZE; j+= 4096)
    buf[j] = (j & 0xFF) + 1;
    break;
    }
    }

    free(buf);
    return 0;
    }

    Before optimization this test takes ~66 seconds, after optimization
    takes ~56 seconds.

    Signed-off-by: Siarhei Siamashka <siarhei.siamashka@nokia.com>
    Signed-off-by: Kirill A. Shutemov <kirill@shutemov.name>
    ---
    arch/arm/lib/copy_page.S | 21 +++++++++++++--------
    1 files changed, 13 insertions(+), 8 deletions(-)

    diff --git a/arch/arm/lib/copy_page.S b/arch/arm/lib/copy_page.S
    index 6ae04db..3bd1b9c 100644
    --- a/arch/arm/lib/copy_page.S
    +++ b/arch/arm/lib/copy_page.S
    @@ -13,7 +13,13 @@
    #include <asm/assembler.h>
    #include <asm/asm-offsets.h>

    -#define COPY_COUNT (PAGE_SZ/64 PLD( -1 ))
    +#if CONFIG_ARCH_OMAP3
    +#define CACHE_LINE_SZ 64
    +#else
    +#define CACHE_LINE_SZ 32
    +#endif
    +
    +#define COPY_COUNT (PAGE_SZ/(2 * CACHE_LINE_SZ) PLD( -1 ))

    .text
    .align 5
    @@ -26,17 +32,16 @@
    ENTRY(copy_page)
    stmfd sp!, {r4, lr} @ 2
    PLD( pld [r1, #0] )
    - PLD( pld [r1, #32] )
    + PLD( pld [r1, #CACHE_LINE_SZ] )
    mov r2, #COPY_COUNT @ 1
    ldmia r1!, {r3, r4, ip, lr} @ 4+1
    -1: PLD( pld [r1, #64] )
    - PLD( pld [r1, #96] )
    -2: stmia r0!, {r3, r4, ip, lr} @ 4
    - ldmia r1!, {r3, r4, ip, lr} @ 4+1
    - stmia r0!, {r3, r4, ip, lr} @ 4
    - ldmia r1!, {r3, r4, ip, lr} @ 4+1
    +1: PLD( pld [r1, #(2*CACHE_LINE_SZ)])
    + PLD( pld [r1, #(3*CACHE_LINE_SZ)])
    +2:
    + .rept (2 * (CACHE_LINE_SZ) / 16 - 1)
    stmia r0!, {r3, r4, ip, lr} @ 4
    ldmia r1!, {r3, r4, ip, lr} @ 4
    + .endr
    subs r2, r2, #1 @ 1
    stmia r0!, {r3, r4, ip, lr} @ 4
    ldmgtia r1!, {r3, r4, ip, lr} @ 4
    --
    1.6.3.3


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