qemu-tsx

Add Transactional Synchronization eXtensions to QEMU

About

Intel's Haswell microarchitecture will support Transactional Synchronization eXtensions (TSX) including Restricted Transactional Memory (RTM) and Hardware Lock Elision (HLE). The specification can be found at http://software.intel.com/sites/default/files/m/3/2/1/0/b/41417-319433-012.pdf

This project is an implementation of TSX on top of the QEMU emulator.

Installation

./configure --target-list=x86_64-softmmu

make

make install

Usage

qemu-system-x86_64 -cpu Haswell

This creates a file 'execlog', which can be parsed with 'htmtest/parselog.py'.

Design

Several changes were made to the i386 target to support TSX:

• New cpu type "Haswell". '-cpu Haswell' must be specified on the command line to QEMU to support TSX instructions.
• New common memory interface in 'target-i386/mem_wrap.h'. This is used to wrap all memory micro-operations in 'target-i386/translate.c' to efficiently switch behavior when RTM mode is active.
• Changes to CPUX86State to support RTM and store register state.
• Simulate a configurable transaction cache with 64 byte cache lines.
• Instruction interleaving. To force as much contention as possible (and really stress the design) QEMU was modified to execute one emulated instruction at a time on processors in transactional mode before yielding to other emulated processors. This mode can be explicitly triggered using the dummy interrupt 'int $0xFF' and exited using the dummy interrupt 'int $0xFE'. This can be enabled by the command line option -txstep

Features

• Configurable caches (defaulting to 32KB 8-way set associative). See target-i386/tsx_cache.h
• Non-transactional memory access killing transactions.

See also

For userspace: Intel's SDE (http://software.intel.com/en-us/articles/intel-software-development-emulator).

TODO

• Implement Hardware Lock Elision (HLE). Probably not that difficult given RTM is implemented. project does not yet support it.