Supporting write-through caching with high-performance TSO for resilient CXL systems
Ocalan, Burak
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https://hdl.handle.net/2142/129929
Description
Title
Supporting write-through caching with high-performance TSO for resilient CXL systems
Author(s)
Ocalan, Burak
Issue Date
2025-07-11
Director of Research (if dissertation) or Advisor (if thesis)
Torrellas, Josep
Department of Study
Siebel School Comp & Data Sci
Discipline
Computer Science
Degree Granting Institution
University of Illinois Urbana-Champaign
Degree Name
M.S.
Degree Level
Thesis
Keyword(s)
Write-through
Tso
Cxl
Language
eng
Abstract
Current multiprocessors that support the total store order (TSO) memory consistency model invariably use write-back (WB) caches. When their hardware needs to issue write-through (WT) stores as in uncached operations, they deliver dismal performance: writes to memory have to be fully serialized, often forcing the program to observe the full latency of a round-trip to memory. To solve this problem, this thesis presents a novel architecture that supports high-performance TSO for WT caching environments. The architecture, called PhasedStore, involves extending the store queue of the core with additional states. Individual WT stores operate in two phases, which allow them to fully overlap with other stores and still satisfy TSO. PhasedStore is useful in environments that require a WT cache coherence protocol. This is the case in a setting that this thesis explores: a cache-coherent CXL distributed shared memory system in the presence of compute node failures. In this environment, to simplify recovery, we support a WT directory-based protocol which guarantees that stores are propagated to the CXL memory before updating the caches. Our evaluation shows that PhasedStore is very effective. Compared to a conventional approach to enforce TSO in a WT protocol, PhasedStore reduces the average execution time of a set of parallel applications by 2.21x. Further, the applications' execution time is only 1.40x higher than with a TSO WB protocol that includes no resilience consideration.
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