ada543459c
Add support for the AMD Fam19h 16-deep branch sampling feature as described in the AMD PPR Fam19h Model 01h Revision B1. This is a model specific extension. It is not an architected AMD feature. The Branch Sampling (BRS) operates with a 16-deep saturating buffer in MSR registers. There is no branch type filtering. All control flow changes are captured. BRS relies on specific programming of the core PMU of Fam19h. In particular, the following requirements must be met: - the sampling period be greater than 16 (BRS depth) - the sampling period must use a fixed and not frequency mode BRS interacts with the NMI interrupt as well. Because enabling BRS is expensive, it is only activated after P event occurrences, where P is the desired sampling period. At P occurrences of the event, the counter overflows, the CPU catches the interrupt, activates BRS for 16 branches until it saturates, and then delivers the NMI to the kernel. Between the overflow and the time BRS activates more branches may be executed skewing the period. All along, the sampling event keeps counting. The skid may be attenuated by reducing the sampling period by 16 (subsequent patch). BRS is integrated into perf_events seamlessly via the same PERF_RECORD_BRANCH_STACK sample format. BRS generates perf_branch_entry records in the sampling buffer. No prediction information is supported. The branches are stored in reverse order of execution. The most recent branch is the first entry in each record. No modification to the perf tool is necessary. BRS can be used with any sampling event. However, it is recommended to use the RETIRED_BRANCH_INSTRUCTIONS event because it matches what the BRS captures. $ perf record -b -c 1000037 -e cpu/event=0xc2,name=ret_br_instructions/ test $ perf report -D 56531696056126 0x193c000 [0x1a8]: PERF_RECORD_SAMPLE(IP, 0x2): 18122/18230: 0x401d24 period: 1000037 addr: 0 ... branch stack: nr:16 ..... 0: 0000000000401d24 -> 0000000000401d5a 0 cycles 0 ..... 1: 0000000000401d5c -> 0000000000401d24 0 cycles 0 ..... 2: 0000000000401d22 -> 0000000000401d5c 0 cycles 0 ..... 3: 0000000000401d5e -> 0000000000401d22 0 cycles 0 ..... 4: 0000000000401d20 -> 0000000000401d5e 0 cycles 0 ..... 5: 0000000000401d3e -> 0000000000401d20 0 cycles 0 ..... 6: 0000000000401d42 -> 0000000000401d3e 0 cycles 0 ..... 7: 0000000000401d3c -> 0000000000401d42 0 cycles 0 ..... 8: 0000000000401d44 -> 0000000000401d3c 0 cycles 0 ..... 9: 0000000000401d3a -> 0000000000401d44 0 cycles 0 ..... 10: 0000000000401d46 -> 0000000000401d3a 0 cycles 0 ..... 11: 0000000000401d38 -> 0000000000401d46 0 cycles 0 ..... 12: 0000000000401d48 -> 0000000000401d38 0 cycles 0 ..... 13: 0000000000401d36 -> 0000000000401d48 0 cycles 0 ..... 14: 0000000000401d4a -> 0000000000401d36 0 cycles 0 ..... 15: 0000000000401d34 -> 0000000000401d4a 0 cycles 0 ... thread: test:18230 ...... dso: test Signed-off-by: Stephane Eranian <eranian@google.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lore.kernel.org/r/20220322221517.2510440-4-eranian@google.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.