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HP OpenVMS Systemsask the wizard |
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The Question is: In a previous "Ask the Wizard" article (6984 & 7383) the OpenVMS Wizard stated: "The interlocked instructions can typically lock ranges of memory rather larger than the target bit (or target queue entry), ... thus bitlocks located near each other in virtual memory have unexpected contention. This contention will not disrupt the corre ct opreration of the bitlocks, but it can slow the access to the bitlocks." You mention that the granularity of memory affected by a hardware interlock is implementation specific, but where can we find out what this is for various OS versions/hardware, especially OpenVMS v7.3-1 and ES40/45s hardware ? The Answer is : There is no particular specification of this value, and the granularity of the memory interlock mechanism can be any value from an aligned longword to all of system physical memory on VAX and a quadword to 128 bytes (recommended) to all of physical memory on Alpha -- this interlock granularity decision is otherwise left entirely to the particular platform design team(s) involved. The answer to your question is thus a generic 128 byte separation recommendation, and a further recommendation that you not code any further derivative assumptions into applications. For related (supporting) information, please see the Alpha LDx_L and STx_C mechanisms. For additional related information, please see the 21264 directory on Freeware V4.0 and the SRM_CHECK tool.
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