instrumentation: Show additional TSC clock source info in pg_test_timing#71
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instrumentation: Show additional TSC clock source info in pg_test_timing#71lfittl wants to merge 2 commits into
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This restricts the retrieval of the TSC frequency whilst under a Hypervisor to either Hypervisor-specific CPUID registers (0x40000010), or TSC calibration. We previously allowed retrieving from the traditional CPUID registers for TSC frequency (0x15/0x16) like on bare metal, but that is not trustworthy and can report a wildly incorrect frequency, like 7 kHz when the actual calibrated frequencty is 2.5 GHz. Per report from buildfarm member drongo. Author: Lukas Fittl <lukas@fittl.com> Discussion: https://www.postgresql.org/message-id/flat/jr4hk2sxhqcfpb67ftz5g4vw33nm67cgf7go3wwmqsafu5aclq%405m67ukuhyszz#2fdfd95b6a4a74410196999818e16cfc
In some cases its needed to understand whether TSC frequency data was sourced from CPUID, and which of the registers. This shows this debug information at the end of pg_test_timing, through use of a new pg_timing_tsc_clock_source_info function, replacing the previous pg_tsc_calibrate_frequency export that was only needed for debug info. Author: Lukas Fittl <lukas@fittl.com> Suggested-by: Andres Freund <andres@anarazel.de> Discussion: https://www.postgresql.org/message-id/flat/jr4hk2sxhqcfpb67ftz5g4vw33nm67cgf7go3wwmqsafu5aclq%405m67ukuhyszz#2fdfd95b6a4a74410196999818e16cfc
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