RFR: 8264543: Cross modify fence optimization for x86

[Xubo Zhang]

On Fri, 2 Apr 2021 23:14:44 GMT, Xubo Zhang <github.com+58006833+xbzhang99 at openjdk.org> wrote:

> Intel introduced a new instruction “serialize” which ensures that all modifications to flags, registers, and memory by previous instructions are completed and all buffered writes are drained to memory before the next instruction is fetched and executed. It is a serializing instruction and can be used to implement cross modify fence (OrderAccess::cross_modify_fence_impl) more efficiently than using “cpuid” on supported 32-bit and 64-bit x86 platforms.
> 
> The availability of the SERIALIZE instruction is indicated by the presence of the CPUID feature flag SERIALIZE, bit 14 of the EDX register in sub-leaf CPUID:7H.0H.
> 
> https://software.intel.com/content/www/us/en/develop/download/intel-architecture-instruction-set-extensions-programming-reference.html

Hi Gerard,
Although we don't have benchmark data yet, serialize is the recommended alternative vs. using CPUID. Also, in the virtual machine environment, serialize provides full/fast serialization without causing VMEXIT

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PR: https://git.openjdk.java.net/jdk/pull/3334