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Date: Wed, 14 Mar 2007 17:31:57 +1100 From: Rusty Russell <rusty@...tcorp.com.au> To: Andi Kleen <ak@....de> Cc: lkml - Kernel Mailing List <linux-kernel@...r.kernel.org> Subject: Re: [PATCH] Introduce load_TLS to the "for" loop. On Tue, 2007-03-13 at 14:50 +0100, Andi Kleen wrote: > On Tue, Mar 13, 2007 at 05:39:36PM +1100, Rusty Russell wrote: > > GCC (4.1 at least) unrolls it anyway, but I can't believe this code > > Are you sure? Normally it doesn't unroll without -funroll-loops which > the kernel does normally not set. Especially not with -Os builds. Yep, checked again: $ gcc --version gcc (GCC) 4.1.2 20060928 (prerelease) (Ubuntu 4.1.1-13ubuntu5) ... ... gcc -Wp,-MD,arch/x86_64/kernel/.process.o.d -nostdinc -isystem /usr/lib/gcc/i486-linux-gnu/4.1.2/include -D__KERNEL__ -Iinclude -include include/linux/autoconf.h -Wall -Wundef -Wstrict-prototypes -Wno-trigraphs -fno-strict-aliasing -fno-common -O2 -mtune=generic -m64 -mno-red-zone -mcmodel=kernel -pipe -fno-reorder-blocks -Wno-sign-compare -fno-asynchronous-unwind-tables -funit-at-a-time -mno-sse -mno-mmx -mno-sse2 -mno-3dnow -maccumulate-outgoing-args -fno-omit-frame-pointer -fno-optimize-sibling-calls -g -fno-stack-protector -Wdeclaration-after-statement -Wno-pointer-sign -D"KBUILD_STR(s)=#s" -D"KBUILD_BASENAME=KBUILD_STR(process)" -D"KBUILD_MODNAME=KBUILD_STR(process)" -c -o arch/x86_64/kernel/process.o arch/x86_64/kernel/process.c ... $ objdump -Dr arch/x86_64/kernel/process.o | less ... 6be: 48 8b 94 00 00 00 00 mov 0x0(%rax,%rax,1),%rdx 6c5: 00 6c2: R_X86_64_32S cpu_gdt_descr+0x2 6c6: 48 8b 83 98 02 00 00 mov 0x298(%rbx),%rax 6cd: 48 83 c2 60 add $0x60,%rdx 6d1: 48 89 02 mov %rax,(%rdx) 6d4: 48 8b 83 a0 02 00 00 mov 0x2a0(%rbx),%rax 6db: 48 89 42 08 mov %rax,0x8(%rdx) 6df: 48 8b 83 a8 02 00 00 mov 0x2a8(%rbx),%rax 6e6: 48 89 42 10 mov %rax,0x10(%rdx) If I turn on CONFIG_OPTIMIZE_FOR_SIZE, it's still unrolled, interestingly. Cheers, Rusty. - 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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