US 7689778

Patent Overview: US7689778B2 — "Preventing system snoop and cross-snoop conflicts"

Title: Preventing system snoop and cross-snoop conflicts
Patent number: US7689778B2 (application US11/000,768)
Original assignee: Intel Corp; current assignee listed as Tahoe Research Ltd
Inventors: Yen-Cheng Liu, Krishnakanth V. Sistla, George Cai, Jeffrey D. Gilbert
Priority/filing date: 2004-11-30 | Grant date: 2010-03-30 | Adjusted expiration: 2026-08-18 (status listed Active)
Source: https://patents.google.com/patent/[US7689778](/patent/US7689778)/en

Purpose. The patent addresses cache access conflicts in multi-core processors and multi-processor systems where an "external agent" (e.g., another processor) snoops an inclusive last-level cache (LLC) at substantially the same time a core cross-snoops another core's cache. The excerpt identifies four conflict windows: before the core lookup/cross-snoop; while a cross-snoop is pending; after cross-snoop initiation while the requesting core awaits data; and after data returns but before the LLC is updated. The problem is said to worsen as core count grows.

Plain-language scope. Embodiments use cache bridge scheduling and ordering (CBSO) logic, with internal/external request queues, to manage LLC accesses from external and core agents. In one approach, an external agent's snoops are speculatively blocked once a core gains ownership of the LLC line: pending external accesses are held until the core de-asserts a snoop-blocking signal. If the core request is confirmed as a cross-snoop, no unblock signal is sent at the scheduled cycle; unblocking instead occurs when the cross snoop completes. A second technique (cross-snoop blocking) is also described. Figures cover a caching bridge architecture, speculative snoop blocking, and front-side-bus and point-to-point systems.

What the excerpt does not establish. The supplied text omits the full claims, detailed description, references, and figures' contents. It does not provide claim language, exact signal timing values, the complete cross-snoop blocking flow, or any specification of coherency protocol details beyond incidental mentions. It also does not establish prosecution history, claim construction, or the accuracy of the listed legal status. Claims should be consulted directly at the source URL.