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Date: Wed, 29 Jun 2011 06:36:46 +0800 From: ling.ma@...el.com To: mingo@...e.hu Cc: hpa@...or.com, tglx@...utronix.de, linux-kernel@...r.kernel.org, ling.ma@...el.com Subject: [PATCH RFC 1/2 ] [x86] Optimize copy-page by reducing impact from HW prefetch From: Ma Ling <ling.ma@...el.com> Program's temporal & spatial locality introduce cache unit to overcome the processor-memory performance gap, hardware prefetch is very important to improve performance by reducing cache miss. Modern CPU micro-architecture mainly support two kinds of prefetch mechanism in L1 data cache: a. Data cache unit (DCU) prefetcher. Data spatial locality ask us to provide adjacent data while handling current data. larger cache line size is one choice, but it would cause more cached data to be evicted and latency to load, so we simply prefetch next line when accessing current data. This mode only prefetch data of ascending address. b. Instruction pointer (IP)- based strided prefetcher. Based on Load/write instruction address the mechanism predicate to prefetch data with adaptive stride, including ascending and descending address DCU mode is good when time program data operation spend is longer than that of prefetch next line, however copy-page function breaks the assumption, DCU mode is hardly helpful, specially we append software prefetch and data is in cache, so bus traffic is more busy that impact perforamnce seriously. In this patch we introduce backward copy to successfully avoid HW prfetch impact(DCU prefetcher), and simplify original code. The performance on atom is improved about 11%, 8% on hot/cold-cache case respectively. (We use our micro-benchmark, and will do further test according to your requirement) Thanks Ling --- In this version we re-use prefetcht0 for atom cpu, although prefetchnta is better on snb. arch/x86/lib/copy_page_64.S | 140 +++++++++++++++++++----------------------- 1 files changed, 63 insertions(+), 77 deletions(-) diff --git a/arch/x86/lib/copy_page_64.S b/arch/x86/lib/copy_page_64.S index 45f7db7..35e08fe 100644 --- a/arch/x86/lib/copy_page_64.S +++ b/arch/x86/lib/copy_page_64.S @@ -1,4 +1,5 @@ /* Written 2003 by Andi Kleen, based on a kernel by Evandro Menezes */ +/* Updated 2011 by Ma Ling to introduce backward copy */ #include <linux/linkage.h> #include <asm/dwarf2.h> @@ -13,89 +14,74 @@ copy_page_rep: CFI_ENDPROC ENDPROC(copy_page_rep) -/* - Don't use streaming copy unless cpu indicate X86_FEATURE_REP_GOOD - Could vary the prefetch distance based on SMP/UP -*/ - +/* + * Don't use streaming copy unless cpu indicate X86_FEATURE_REP_GOOD. + * By backward copy we manage to reduce impact from HW prefetch + * when data is in L1 cache, and get benefit when data is not in L1 cache. + */ ENTRY(copy_page) CFI_STARTPROC - subq $3*8, %rsp - CFI_ADJUST_CFA_OFFSET 3*8 - movq %rbx, (%rsp) - CFI_REL_OFFSET rbx, 0 - movq %r12, 1*8(%rsp) - CFI_REL_OFFSET r12, 1*8 - movq %r13, 2*8(%rsp) - CFI_REL_OFFSET r13, 2*8 - - movl $(4096/64)-5, %ecx - .p2align 4 + lea 4096(%rsi), %rsi + lea 4096(%rdi), %rdi + mov $(4096/64)-5, %cl + mov $5, %dl + /* + * Nop force following instruction to be 16 bytes aligned. + */ + nop .Loop64: - dec %rcx - - movq 0x8*0(%rsi), %rax - movq 0x8*1(%rsi), %rbx - movq 0x8*2(%rsi), %rdx - movq 0x8*3(%rsi), %r8 - movq 0x8*4(%rsi), %r9 - movq 0x8*5(%rsi), %r10 - movq 0x8*6(%rsi), %r11 - movq 0x8*7(%rsi), %r12 - - prefetcht0 5*64(%rsi) - - movq %rax, 0x8*0(%rdi) - movq %rbx, 0x8*1(%rdi) - movq %rdx, 0x8*2(%rdi) - movq %r8, 0x8*3(%rdi) - movq %r9, 0x8*4(%rdi) - movq %r10, 0x8*5(%rdi) - movq %r11, 0x8*6(%rdi) - movq %r12, 0x8*7(%rdi) - - leaq 64 (%rsi), %rsi - leaq 64 (%rdi), %rdi - - jnz .Loop64 - - movl $5, %ecx - .p2align 4 + prefetcht0 -5*64(%rsi) + decb %cl + + movq -0x8*1(%rsi), %rax + movq -0x8*2(%rsi), %r8 + movq -0x8*3(%rsi), %r9 + movq -0x8*4(%rsi), %r10 + movq %rax, -0x8*1(%rdi) + movq %r8, -0x8*2(%rdi) + movq %r9, -0x8*3(%rdi) + movq %r10, -0x8*4(%rdi) + + movq -0x8*5(%rsi), %rax + movq -0x8*6(%rsi), %r8 + movq -0x8*7(%rsi), %r9 + movq -0x8*8(%rsi), %r10 + leaq -64(%rsi), %rsi + movq %rax, -0x8*5(%rdi) + movq %r8, -0x8*6(%rdi) + movq %r9, -0x8*7(%rdi) + movq %r10, -0x8*8(%rdi) + leaq -64(%rdi), %rdi + + jnz .Loop64 + .Loop2: - decl %ecx - - movq 0x8*0(%rsi), %rax - movq 0x8*1(%rsi), %rbx - movq 0x8*2(%rsi), %rdx - movq 0x8*3(%rsi), %r8 - movq 0x8*4(%rsi), %r9 - movq 0x8*5(%rsi), %r10 - movq 0x8*6(%rsi), %r11 - movq 0x8*7(%rsi), %r12 - - movq %rax, 0x8*0(%rdi) - movq %rbx, 0x8*1(%rdi) - movq %rdx, 0x8*2(%rdi) - movq %r8, 0x8*3(%rdi) - movq %r9, 0x8*4(%rdi) - movq %r10, 0x8*5(%rdi) - movq %r11, 0x8*6(%rdi) - movq %r12, 0x8*7(%rdi) + decb %dl + + movq -0x8*1(%rsi), %rax + movq -0x8*2(%rsi), %r8 + movq -0x8*3(%rsi), %r9 + movq -0x8*4(%rsi), %r10 + movq %rax, -0x8*1(%rdi) + movq %r8, -0x8*2(%rdi) + movq %r9, -0x8*3(%rdi) + movq %r10, -0x8*4(%rdi) + + movq -0x8*5(%rsi), %rax + movq -0x8*6(%rsi), %r8 + movq -0x8*7(%rsi), %r9 + movq -0x8*8(%rsi), %r10 + leaq -64(%rsi), %rsi + movq %rax, -0x8*5(%rdi) + movq %r8, -0x8*6(%rdi) + movq %r9, -0x8*7(%rdi) + movq %r10, -0x8*8(%rdi) + leaq -64(%rdi), %rdi + + jnz .Loop2 - leaq 64(%rdi), %rdi - leaq 64(%rsi), %rsi - - jnz .Loop2 - - movq (%rsp), %rbx - CFI_RESTORE rbx - movq 1*8(%rsp), %r12 - CFI_RESTORE r12 - movq 2*8(%rsp), %r13 - CFI_RESTORE r13 - addq $3*8, %rsp - CFI_ADJUST_CFA_OFFSET -3*8 ret + .Lcopy_page_end: CFI_ENDPROC ENDPROC(copy_page) -- 1.6.5.2 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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