Details
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Bug
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Status: Open (View Workflow)
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Minor
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Resolution: Unresolved
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None
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None
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ARM64
Description
my_convert() in strings/ctype.c has this special optimization for i386 and x86_64:
#if defined(__i386__) || defined(__x86_64__)
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/* |
Special loop for i386, it allows to refer to a
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non-aligned memory block as UINT32, which makes
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it possible to copy four bytes at once. This
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gives about 10% performance improvement comparing
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to byte-by-byte loop.
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*/
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for ( ; length >= 4; length-= 4, from+= 4, to+= 4) |
{
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if ((*(uint32*)from) & 0x80808080) |
break; |
*((uint32*) to)= *((const uint32*) from); |
}
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#endif /* __i386__ */
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... /* Unoptimized bytewise processing goes here */ |
Two things can be improved about that code:
1. 64-bit architectures like x86_64 could be optimized even further by processing 8 bytes at a time;
2. Other 64-bit architectures like aarch64 could also benefit from the same optimization, rather than process the input byte by byte.
In our case we see a few percent improvement in CPU-bound sysbench OLTP RO on AArch64, which is not too bad for such a simple optimization.