NoSQ: Store-Load Communication without a Store Queue
Tingting Sha
Martin, M.M.K.
Amir Roth
Dept. of Comput. & Inf. Sci., Pennsylvania Univ., Philadelphia, PA;
This paper appears in: Microarchitecture, 2006. MICRO-39. 39th Annual IEEE/ACM International Symposium on
Publication Date: 9-13 Dec. 2006
On page(s): 285-296
Location: Orlando, FL,
ISSN: 1072-4451
ISBN: 0-7695-2732-9
INSPEC Accession Number: 9452028
Digital Object Identifier: 10.1109/MICRO.2006.39
Current Version Published: 2006-12-26
Abstract
This paper presents NoSQ (short for no store queue), a microarchitecture that performs store-load communication without a store queue and without executing stores in the out-of-order engine. NoSQ implements store-load communication using speculative memory bypassing (SMB), the dynamic short-circuiting of DEF-store-load-USE chains to DEF-USE chains. Whereas previous proposals used SMB as an opportunistic complement to conventional store queue-based forwarding, NoSQ uses SMB as a store queue replacement. NoSQ relies on two supporting mechanisms. The first is an advanced store-load bypassing predictor that for a given dynamic load can predict whether that load will bypass and the identity of the communicating store. The second is an efficient verification mechanism for both bypassed and non-bpyassed loads using in-order load re-execution with an SMB-aware store vulnerability window (SVW) filter. The primary benefit of NoSQ is a simple, fast datapath that does not contain store-load forwarding hardware; all loads get their values either from the data cache or from the register file. Experiments show that this simpler design - despite being more speculative - slightly outperforms a conventional store-queue based design on most benchmarks (by 2% on average)
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