A storage efficient last-level branch target buffer based on dynamic compression
With the increasing size and complexity of software systems,the massive instructions bring frequent misses to instruction caches and branch target buffers(BTBs)and hurt central processing unit(CPU)performance.Modern industry CPU designs utilize sufficiently large multi-level BTBs in decoupled front end to reduce performance degra-dation from misses and consequently result in vast BTB storage requirements.However,current compressed BTBs use statical allocation policies that cannot adapt to upcoming branches.To overcome the limitations of current BT-Bs,this work proposes a dynamically compressed BTB called zipped branch target buffer(ZBTB).ZBTB uses an adaptive allocation policy enabled by the employment of variable length target offset with a storage-free least-re-cently-used(LRU)replacement and skewed associativity to reduce conflictions.Evaluate ZBTB on traces from the First Instruction Prefetching Championship(IPC-1).Compared with the state-of-the-art storage-efficient BTBs,ZBTB can reduce the misses by over 66％with the 33.5 kB storage budget.
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