47125db27e
Last Branch Records (LBR) enables recording of software path history by logging taken branches and other control flows within architectural registers now. Intel CPUs have had model-specific LBR for quite some time, but this evolves them into an architectural feature now. The main improvements of Architectural LBR implemented includes: - Linux kernel can support the LBR features without knowing the model number of the current CPU. - Architectural LBR capabilities can be enumerated by CPUID. The lbr_ctl_map is based on the CPUID Enumeration. - The possible LBR depth can be retrieved from CPUID enumeration. The max value is written to the new MSR_ARCH_LBR_DEPTH as the number of LBR entries. - A new IA32_LBR_CTL MSR is introduced to enable and configure LBRs, which replaces the IA32_DEBUGCTL[bit 0] and the LBR_SELECT MSR. - Each LBR record or entry is still comprised of three MSRs, IA32_LBR_x_FROM_IP, IA32_LBR_x_TO_IP and IA32_LBR_x_TO_IP. But they become the architectural MSRs. - Architectural LBR is stack-like now. Entry 0 is always the youngest branch, entry 1 the next youngest... The TOS MSR has been removed. The way to enable/disable Architectural LBR is similar to the previous model-specific LBR. __intel_pmu_lbr_enable/disable() can be reused, but some modifications are required, which include: - MSR_ARCH_LBR_CTL is used to enable and configure the Architectural LBR. - When checking the value of the IA32_DEBUGCTL MSR, ignoring the DEBUGCTLMSR_LBR (bit 0) for Architectural LBR, which has no meaning and always return 0. - The FREEZE_LBRS_ON_PMI has to be explicitly set/clear, because MSR_IA32_DEBUGCTLMSR is not touched in __intel_pmu_lbr_disable() for Architectural LBR. - Only MSR_ARCH_LBR_CTL is cleared in __intel_pmu_lbr_disable() for Architectural LBR. Some Architectural LBR dedicated functions are implemented to reset/read/save/restore LBR. - For reset, writing to the ARCH_LBR_DEPTH MSR clears all Arch LBR entries, which is a lot faster and can improve the context switch latency. - For read, the branch type information can be retrieved from the MSR_ARCH_LBR_INFO_*. But it's not fully compatible due to OTHER_BRANCH type. The software decoding is still required for the OTHER_BRANCH case. LBR records are stored in the age order as well. Reuse intel_pmu_store_lbr(). Check the CPUID enumeration before accessing the corresponding bits in LBR_INFO. - For save/restore, applying the fast reset (writing ARCH_LBR_DEPTH). Reading 'lbr_from' of entry 0 instead of the TOS MSR to check if the LBR registers are reset in the deep C-state. If 'the deep C-state reset' bit is not set in CPUID enumeration, ignoring the check. XSAVE support for Architectural LBR will be implemented later. The number of LBR entries cannot be hardcoded anymore, which should be retrieved from CPUID enumeration. A new structure x86_perf_task_context_arch_lbr is introduced for Architectural LBR. Signed-off-by: Kan Liang <kan.liang@linux.intel.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lkml.kernel.org/r/1593780569-62993-15-git-send-email-kan.liang@linux.intel.com |
||
|---|---|---|
| Documentation | ||
| LICENSES | ||
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| ipc | ||
| kernel | ||
| lib | ||
| mm | ||
| net | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
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 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.