Measuring Latency in Linux (2014)

Re:Measuring Latency in Linux (2014) by jsolson on Thursday February 27, 2020 @09:56PM (#22440128)

Intel's VMCS includes a TSC offset field as well as TSC scaling. These allow for a stable RDTSC across migrations between hosts, modulo actual time lost to migration blackout.

(I work on virtualization in GCE)

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Re:Measuring Latency in Linux (2014) by xakahnx on Friday February 28, 2020 @12:04AM (#22440645)

Cool! I looked up more info on this and ended up here, http://www.brendangregg.com/blog/2017-05-04/the-pmcs-of-ec2....

But I only skimmed this and I don't see that it mentions about migration across hosts. Only that the hypervisor is able to expose the MSRs or PMCs.

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Re:Measuring Latency in Linux (2014) by BeeOnRope on Thursday February 27, 2020 @10:20PM (#22440231)

So do gettimeofday and the various clock_gettime methods [1] hit the vDSO on GCP, or do they incur a syscall, or something else?

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[1] Not all of the clock_gettime sources hit the vDSO even on bare metal Linux on typical x86 hardware, but many of the important ones do.

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