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VM Time Correlation means determining if each TSC packet belongs to a VM Guest or the Host. When the trace is "in context" that is indicated by the NR flag in the PIP packet. However, when tracing kernel-only, userspace only, or using address filters, the trace can be "out of context" in which case timing packets are produced but not PIP packets. Nevertheless, it is very unlikely the VM Guest timestamps will be in the same range as the Host timestamps. Host time ranges are established by a starting side-band event timestamp, and subsequently by the buffer timestamp, written when the buffer is copied to the perf.data file. This patch supports updating the VM Guest timestamp packets, assuming an unchanging (during perf record) VMX TSC Offset and no VMX TSC scaling. Furthermore, it is possible to determine what the VMX TSC Offset is, although not necessarily at the start. The dry-run option lets that information be determined so that the user can pass it to a subsequent run. For more detail, refer to the example in the Intel PT documentation in a subsequent patch. VM Time Correlation is also performed on the TSC value in PEBs-via-PT records. Signed-off-by: Adrian Hunter <adrian.hunter@intel.com> Reviewed-by: Andi Kleen <ak@linux.intel.com> Cc: Jiri Olsa <jolsa@redhat.com> Link: https://lore.kernel.org/r/20210430070309.17624-12-adrian.hunter@intel.com Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.