Update cpu relax functions #64
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http://github.com/mysql/mysql-server/pull/305 uses an 'isb' which makes the adaptive-spin behavior match x86s
Add support for a define RELAX_IS_ISB that adapts cpu_relax() to using an isb instead of a yield().
rpgolshan
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Sep 17, 2021
| #if defined(__x86_64__) | ||
| asm volatile ("pause" : : : "memory" ); | ||
| #elif defined (__arch64__) | ||
| #elif defined (__aarch64__) && defined(RELAX_IS_ISB) |
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When do you recommend a user enabling this over the default? Can you add a define in the Makefile?
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Without the define, this behaves like the kernel does today. I believe the define improves the performance of the kernel locks but it's not what is committed today.
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Ok so if the kernel changes in the future we just need to expose this define.
| // Theoretically we could emit a yield here but MySQL doesn't do it | ||
| // and most ARM cores are likely to NOP it anyway | ||
| #define UT_RELAX_CPU() asm volatile ("":::"memory") | ||
| #define UT_RELAX_CPU() asm volatile ("isb":::"memory") |
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Update UT_RELAX_CPU to match upstream changes in MySQL
Fix cpu_relax and add RELAX_IS_ISB