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When perf is used in non-system mode, i.e. without specifying CPUs to
count on, check_and_calc_range falls into the case when it sets
M_TC_EN_ALL in the counter config_base. This has the impact of always
counting for all of the threads in a core, even when the user has not
requested it. For example this can be seen with a test program which
executes 30002 instructions and 10000 branches running on one VPE and a
busy load on the other VPE in the core. Without this commit, the
expected count is not returned:
taskset 4 dd if=/dev/zero of=/dev/null count=100000 & taskset 8 perf
stat -e instructions:u,branches:u ./test_prog
Performance counter stats for './test_prog':
103235 instructions:u
17015 branches:u
In order to fix this, remove check_and_calc_range entirely and perform
all of the logic in mipsxx_pmu_enable_event. Since
mipsxx_pmu_enable_event now requires the range of the event, ensure that
it is set by mipspmu_perf_event_encode in the same circumstances as
before (i.e. #ifdef CONFIG_MIPS_MT_SMP && num_possible_cpus() > 1).
The logic of mipsxx_pmu_enable_event now becomes:
If the CPU is a BMIPS5000, then use the special vpe_id() implementation
to select which VPE to count.
If the counter has a range greater than a single VPE, i.e. it is a
core-wide counter, then ensure that the counter is set up to count
events from all TCs (though, since this is true by definition, is this
necessary? Just enabling a core-wide counter in the per-VPE case appears
experimentally to return the same counts. This is left in for now as the
logic was present before).
If the event is set up to count a particular CPU (i.e. system mode),
then the VPE ID of that CPU is used for the counter.
Otherwise, the event should be counted on the CPU scheduling this thread
(this was the critical bit missing from the previous implementation) so
the VPE ID of this CPU is used for the counter.
With this commit, the same test as before returns the counts expected:
taskset 4 dd if=/dev/zero of=/dev/null count=100000 & taskset 8 perf
stat -e instructions:u,branches:u ./test_prog
Performance counter stats for './test_prog':
30002 instructions:u
10000 branches:u
Signed-off-by: Matt Redfearn <matt.redfearn@mips.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Florian Fainelli <f.fainelli@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/19138/
Signed-off-by: James Hogan <jhogan@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 Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.
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.