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71dcc11c2c
Currently when a user samples user space GPRs (--user-regs option) with
PEBS, the user space GPRs actually always come from software PMI
instead of from PEBS hardware. This leads to the sampled GPRs to
possibly be inaccurate for single PEBS record case because of the
skid between counter overflow and GPRs sampling on PMI.
For the large PEBS case, it is even worse. If user sets the
exclude_kernel attribute, large PEBS would be used to sample user space
GPRs, but since PEBS GPRs group is not really enabled, it leads to all
samples in the large PEBS record to share the same piece of user space
GPRs, like this reproducer shows:
$ perf record -e branches:pu --user-regs=ip,ax -c 100000 ./foo
$ perf report -D | grep "AX"
.... AX 0x000000003a0d4ead
.... AX 0x000000003a0d4ead
.... AX 0x000000003a0d4ead
.... AX 0x000000003a0d4ead
.... AX 0x000000003a0d4ead
.... AX 0x000000003a0d4ead
.... AX 0x000000003a0d4ead
.... AX 0x000000003a0d4ead
.... AX 0x000000003a0d4ead
.... AX 0x000000003a0d4ead
.... AX 0x000000003a0d4ead
So enable GPRs group for user space GPRs sampling and prioritize reading
GPRs from PEBS. If the PEBS sampled GPRs is not user space GPRs (single
PEBS record case), perf_sample_regs_user() modifies them to user space
GPRs.
[ mingo: Clarified the changelog. ]
Fixes:
|
||
|---|---|---|
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| io_uring | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| rust | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .clippy.toml | ||
| .cocciconfig | ||
| .editorconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| .rustfmt.toml | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
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 reStructuredText 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.