Almost certainly still faster than bytewise copy!
"Yinghai Lu" <yinghai@xxxxxxxxxx> wrote:
>On 10/07/2010 10:40 PM, tip-bot for Zhao Yakui wrote:
>> Commit-ID: 68f4d5a00adaab33b136fce2c72d5c377b39b0b0
>> Gitweb: http://git.kernel.org/tip/68f4d5a00adaab33b136fce2c72d5c377b39b0b0
>> Author: Zhao Yakui <yakui.zhao@xxxxxxxxx>
>> AuthorDate: Fri, 8 Oct 2010 09:47:33 +0800
>> Committer: H. Peter Anvin <hpa@xxxxxxxxx>
>> CommitDate: Thu, 7 Oct 2010 21:23:09 -0700
>>
>> x86, setup: Use string copy operation to optimze copy in kernel compression
>>
>> The kernel decompression code parses the ELF header and then copies
>> the segment to the corresponding destination. Currently it uses slow
>> byte-copy code. This patch makes it use the string copy operations
>> instead.
>>
>> In the test the copy performance can be improved very significantly after using
>> the string copy operation mechanism.
>> 1. The copy time can be reduced from 150ms to 20ms on one Atom machine
>> 2. The copy time can be reduced about 80% on another machine
>> The time is reduced from 7ms to 1.5ms when using 32-bit kernel.
>> The time is reduced from 10ms to 2ms when using 64-bit kernel.
>>
>> Signed-off-by: Zhao Yakui <yakui.zhao@xxxxxxxxx>
>> LKML-Reference: <1286502453-7043-1-git-send-email-yakui.zhao@xxxxxxxxx>
>> Signed-off-by: H. Peter Anvin <hpa@xxxxxxxxx>
>> ---
>> arch/x86/boot/compressed/misc.c | 29 +++++++++++++++++++++++------
>> 1 files changed, 23 insertions(+), 6 deletions(-)
>>
>> diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
>> index 8f7bef8..23f315c 100644
>> --- a/arch/x86/boot/compressed/misc.c
>> +++ b/arch/x86/boot/compressed/misc.c
>> @@ -229,18 +229,35 @@ void *memset(void *s, int c, size_t n)
>> ss[i] = c;
>> return s;
>> }
>> -
>> +#ifdef CONFIG_X86_32
>> void *memcpy(void *dest, const void *src, size_t n)
>> {
>> - int i;
>> - const char *s = src;
>> - char *d = dest;
>> + int d0, d1, d2;
>> + asm volatile(
>> + "rep ; movsl\n\t"
>> + "movl %4,%%ecx\n\t"
>> + "rep ; movsb\n\t"
>> + : "=&c" (d0), "=&D" (d1), "=&S" (d2)
>> + : "0" (n >> 2), "g" (n & 3), "1" (dest), "2" (src)
>> + : "memory");
>>
>> - for (i = 0; i < n; i++)
>> - d[i] = s[i];
>> return dest;
>> }
>> +#else
>> +void *memcpy(void *dest, const void *src, size_t n)
>> +{
>> + long d0, d1, d2;
>> + asm volatile(
>> + "rep ; movsq\n\t"
>> + "movq %4,%%rcx\n\t"
>> + "rep ; movsb\n\t"
>> + : "=&c" (d0), "=&D" (d1), "=&S" (d2)
>> + : "0" (n >> 3), "g" (n & 7), "1" (dest), "2" (src)
>> + : "memory");
>>
>> + return dest;
>> +}
>> +#endif
>>
>> static void error(char *x)
>> {
>
>wonder if it would have problem with some old AMD K8 systems.
>
>in amd.c
>
> /* On C+ stepping K8 rep microcode works well for copy/memset */
> if (c->x86 == 0xf) {
> u32 level;
>
> level = cpuid_eax(1);
> if ((level >= 0x0f48 && level < 0x0f50) || level >= 0x0f58)
> set_cpu_cap(c, X86_FEATURE_REP_GOOD);
>...
>
> }
> if (c->x86 >= 0x10)
> set_cpu_cap(c, X86_FEATURE_REP_GOOD);
>
>Yinghai
--
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