Discuss about the LLVM SW mitigation to Jump Conditional Code Erratum

Hi all,

We have more data based on LLVM test suite and SPEC2017. It covered the performance, code size and build time. It collected the performance of the SW mitigation on the servers w/o MCU and with MCU, the prefix padding and nop padding, the padding to jcc+fused+jmp and the padding to all types of branches. I expect the data can help us to move forward and make decision.

For the code size of Chrome, Firefox, or Safari, we don’t have data on hand. We are willing to work with community to get those data.

Below is the LLVM test suite we measured including the performance, code size and build time.

The data indicates some performance effect (1.7%) from the microcode update, which was reduced to 0.5% with the SW mitigation of prefix padding. The code size increase in test suite is ~0.5%. And the compile time increase is ~2%.