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c3d78c34ad
CPU_CYCLES is expected to count the logical CPU (PE) clock. Currently it's
preferred to use PMCCNTR_EL0 for counting CPU_CYCLES, but it'll count
processor clock rather than the PE clock (ARM DDI0487 L.b D13.1.3) if
one of the SMT siblings is not idle on a multi-threaded implementation.
So don't use it on SMT cores.
Introduce topology_core_has_smt() for knowing the SMT implementation and
cached it in arm_pmu::has_smt during allocation.
When counting cycles on SMT CPU 2-3 and CPU 3 is idle, without this
patch we'll get:
[root@client1 tmp]# perf stat -e cycles -A -C 2-3 -- stress-ng -c 1
--taskset 2 --timeout 1
[...]
Performance counter stats for 'CPU(s) 2-3':
CPU2 2880457316 cycles
CPU3 2880459810 cycles
1.254688470 seconds time elapsed
With this patch the idle state of CPU3 is observed as expected:
[root@client1 ~]# perf stat -e cycles -A -C 2-3 -- stress-ng -c 1
--taskset 2 --timeout 1
[...]
Performance counter stats for 'CPU(s) 2-3':
CPU2 2558580492 cycles
CPU3 305749 cycles
1.113626410 seconds time elapsed
Signed-off-by: Yicong Yang <yangyicong@hisilicon.com>
Signed-off-by: Will Deacon <will@kernel.org>
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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.