Re: [PATCH] lib/raid6: Add AVX2 optimized recovery functions
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From: Andi Kleen <hidden>
Date: 2012-11-29 20:10:07
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Jim Kukunas [off-list ref] writes:
quoted hunk
+ + /* ymm0 = x0f[16] */ + asm volatile("vpbroadcastb %0, %%ymm7" : : "m" (x0f)); + + while (bytes) { +#ifdef CONFIG_X86_64 + asm volatile("vmovdqa %0, %%ymm1" : : "m" (q[0])); + asm volatile("vmovdqa %0, %%ymm9" : : "m" (q[32])); + asm volatile("vmovdqa %0, %%ymm0" : : "m" (p[0])); + asm volatile("vmovdqa %0, %%ymm8" : : "m" (p[32]));
This is somewhat dangerous to assume registers do not get changed between assembler statements or assembler statements do not get reordered. Better always put such values into explicit variables or merge them into a single asm statement. asm volatile is also not enough to prevent reordering. If anything you would need a memory clobber. -Andi -- ak@linux.intel.com -- Speaking for myself only